Form of Underwriting Agreement

Exhibit 1.1

CONCHO RESOURCES INC.

[          ] Shares of Common Stock

Underwriting Agreement

December [ ], 2007

J.P. Morgan Securities Inc.
Banc of America Securities LLC
      As Representatives of the
      several Underwriters listed
      in Schedule 1 hereto
c/o J.P. Morgan Securities Inc.
277 Park Avenue
New York, New York 10172

Ladies and Gentlemen:

     Chase Oil Corporation and Caza Energy LLC (together, the “Chase Stockholders”) and certain other stockholders named in Schedule 2 (other than the Chase Stockholders) (collectively, the “Non-Chase Stockholders,” and together with Chase Stockholders, the “Selling Stockholders”) propose to sell to the several Underwriters listed in Schedule 1 hereto (the “Underwriters”), for whom you are acting as representatives (collectively, the “Representatives”), an aggregate of [          ] shares of Common Stock, par value $0.001 per share, of Concho Resources Inc., a Delaware corporation (the “Company”). At the option of the Underwriters, the Selling Stockholders named in Schedule 3 hereto (the “Option Selling Stockholders”) propose to sell up to an additional [          ] shares of Common Stock of the Company. The aggregate of [          ] shares which may be sold by the Selling Stockholders is herein called the “Underwritten Shares,” and the aggregate of [          ] additional shares to be sold by the Option Selling Stockholders is herein called the “Option Shares.” The Underwritten Shares and the Option Shares are herein referred to as the “Shares”. The shares of Common Stock of the Company to be outstanding after giving effect to the sale of the Shares are herein referred to as the “Stock”.

     The Selling Stockholders hereby confirm their agreement with the several Underwriters concerning the purchase and sale of the Underwritten Shares to be sold by the Selling Stockholders, and the Option Selling Stockholders hereby confirm their agreement with the several Underwriters concerning the purchase and sale of the Option Shares which may be sold by the Option Selling Stockholders as follows:

     1. Registration Statement. The Company has prepared and filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended, and the rules and regulations of the Commission thereunder (collectively, the “Securities Act”), a registration statement on Form S-1(File No. 333-[          ]) including a prospectus, relating to the Shares. Such registration statement, as amended at the time it becomes effective, including the information, if any, deemed pursuant to Rule 430A, 430B or 430C under the Securities Act to be part of the registration statement at the time of its effectiveness (“Rule 430 Information”), is referred to herein as the “Registration Statement”; and as used herein, the term “Preliminary Prospectus” means each prospectus included in such registration statement (and any amendments thereto) before it becomes effective, any prospectus filed with the Commission pursuant to Rule 424(a) under the Securities Act and the prospectus included in the Registration Statement at the time of its effectiveness that omits Rule 430 Information, and the term “Prospectus” means the prospectus in the form first used (or made available upon the request of purchasers pursuant to Rule 173 under the Securities Act) in connection with confirmation of sales of the Shares. If the Company has filed an abbreviated registration statement pursuant to Rule 462(b) under the Securities Act (the

“Rule 462 Registration Statement”), then any reference herein to the term “Registration Statement” shall be deemed to include such Rule 462 Registration Statement. Capitalized terms used but not defined herein shall have the meanings given to such terms in the Registration Statement and the Prospectus.

     At or prior to the time when sales of the Shares were first made (the “Time of Sale”), the Company had prepared the following information (collectively with the pricing information set forth on Annex D hereto, the “Time of Sale Information”): a Preliminary Prospectus dated December [ ], 2007 (the “Marketing Preliminary Prospectus”), and each “free-writing prospectus” (as defined pursuant to Rule 405 under the Securities Act) listed on Annex C hereto.

     2. Purchase of the Shares by the Underwriters.

     (a) Each Selling Stockholder agrees, severally and not jointly, to sell the Underwritten Shares to the several Underwriters as provided in this Agreement, and each Underwriter, on the basis of the representations, warranties and agreements set forth herein and subject to the conditions set forth herein, agrees, severally and not jointly, to purchase from each Selling Stockholder at a price per share of $[     ] (the “Purchase Price”) the number of Underwritten Shares (to be adjusted by you so as to eliminate fractional shares) determined by multiplying the aggregate number of Underwritten Shares to be sold by such Selling Stockholder as set forth opposite their respective names in Schedule 2 hereto by a fraction, the numerator of which is the aggregate number of Underwritten Shares to be purchased by such Underwriter as set forth opposite the name of such Underwriter in Schedule 1 hereto and the denominator of which is the aggregate number of Underwritten Shares to be purchased by all the Underwriters from all the Selling Stockholders hereunder.

     In addition, the Option Selling Stockholders, as and to the extent indicated in Schedule 3 hereto, agree, to sell the Option Shares to the several Underwriters and the Underwriters shall have the option to purchase at their election all or any portion of the Option Shares at the Purchase Price. The Underwriters, on the basis of the representations and warranties and agreements herein contained and subject to the conditions set forth herein, shall have the option to purchase, severally and not jointly, from the Option Selling Stockholders all or any portion of the Option Shares at the Purchase Price. If any Option Shares are to be purchased, the number of Option Shares to be purchased by each Underwriter shall be the number of Option Shares which bears the same ratio to the aggregate number of Option Shares being purchased as the number of Underwritten Shares set forth opposite the name of such Underwriter in Schedule 1 hereto (or such number increased as set forth in Section 12 hereof) bears to the aggregate number of Underwritten Shares being purchased from the Selling Stockholders by the several Underwriters, subject, however, to such adjustments to eliminate any fractional Shares as the Representatives in their sole discretion shall make. The number of Option Shares to be purchased from each Option Selling Stockholder shall be the number of Option Shares which bears the same ratio to the aggregate number of Option Shares being purchased as the number of Option Shares set forth opposite the name of such Option Selling Stockholder in Schedule 3 hereto bears to the aggregate number of all Option Shares available to be purchased.

     The Underwriters may exercise the option to purchase the Option Shares at any time in whole, or from time to time in part, on or before the thirtieth day following the date of this Agreement, by written notice from the Representatives to the Company and the Option Selling Stockholders. Such notice shall set forth the aggregate number of Option Shares as to which the option is being exercised and the date and time when the Option Shares are to be delivered and paid for which may be the same date and time as the Closing Date (as hereinafter defined) but shall not be earlier than the Closing Date nor later than the tenth full business day (as hereinafter defined) after the date of such notice (unless such time and date are postponed in accordance with the provisions of Section 12 hereof). Any such notice shall be given at least two Business Days prior to the date and time of delivery specified therein.

     (b) The Company and the Selling Stockholders understand that the Underwriters intend to make a public offering of the Shares as soon after the effectiveness of this Agreement as in the judgment

of the Representatives is advisable, and initially to offer the Shares on the terms set forth in the Prospectus. The Company and the Selling Stockholders acknowledge and agree that the Underwriters may offer and sell Shares to or through any affiliate of an Underwriter and that any such affiliate may offer and sell Shares purchased by it to or through any Underwriter.

     (c) Payment for the Shares shall be made by wire transfer in immediately available funds to the accounts specified by the Selling Stockholders to the Representatives in the case of the Underwritten Shares, at the offices of Vinson & Elkins L.L.P., 1001 Fannin Street, Houston, Texas, 77002 at 10:00 A.M. Houston time on December [ ], 2007, or at such other time or place on the same or such other date, not later than the fifth business day thereafter, as the Representatives, the Company and the Selling Stockholders may agree upon in writing or, in the case of the Option Shares, on the date and at the time and place specified by the Representatives in the written notice of the Underwriters’ election to purchase such Option Shares. The time and date of such payment for the Underwritten Shares is referred to herein as the “Closing Date” and the time and date for such payment for the Option Shares, if other than the Closing Date, is herein referred to as the “Additional Closing Date”.

     Payment for the Shares to be purchased on the Closing Date or the Additional Closing Date, as the case may be, shall be made against delivery through the facilities of the Depository Trust Company (“DTC”) to the Representatives for the respective accounts of the several Underwriters of the Shares to be purchased on such date in definitive form registered in such names and in such denominations as the Representatives shall request in writing not later than two full business days prior to the Closing Date or the Additional Closing Date, as the case may be, with any transfer taxes payable in connection with the sale of the Shares duly paid by the Selling Stockholders or the Option Selling Stockholders, as the case may be. Any certificates for the Shares will be made available for inspection and packaging by the Representatives at the office of DTC or its designated custodian not later than 1:00 P.M., Houston time, on the business day prior to the Closing Date or the Additional Closing Date, as the case may be.

     (d) The Company and the Selling Stockholders acknowledge and agree that the Underwriters are acting solely in the capacity of an arm’s length contractual counterparty to the Company and the Selling Stockholders with respect to the offering of Shares contemplated hereby (including in connection with determining the terms of the offering) and not as a financial advisor or a fiduciary to, or an agent of, the Company, the Selling Stockholders or any other person. Additionally, neither the Representatives nor any other Underwriter is advising the Company, the Selling Stockholders or any other person as to any legal, tax, investment, accounting or regulatory matters in any jurisdiction. The Company and the Selling Stockholders shall consult with their own advisors concerning such matters and shall be responsible for making their own independent investigation and appraisal of the transactions contemplated hereby, and the Underwriters shall have no responsibility or liability to the Company or the Selling Stockholders with respect thereto. Any review by the Underwriters of the Company or the Selling Stockholders, the transactions contemplated hereby or other matters relating to such transactions will be performed solely for the benefit of the Underwriters and shall not be on behalf of the Company or the Selling Stockholders.

     3. Representations and Warranties of the Company. The Company represents and warrants to each Underwriter and each Selling Stockholder that:

     (a) Preliminary Prospectus. No order preventing or suspending the use of any Preliminary Prospectus has been issued by the Commission, and the Marketing Preliminary Prospectus, at the time of filing thereof, complied in all material respects with the Securities Act and did not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any state-

ments or omissions made in reliance upon and in conformity with information relating to any Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for use in the Marketing Preliminary Prospectus.

     (b) Time of Sale Information. The Time of Sale Information, at the Time of Sale did not, and at the Closing Date and as of the Additional Closing Date, as the case may be, will not, contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in reliance upon and in conformity with information relating to any Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for use in such Time of Sale Information. No statement of material fact included in the Prospectus has been omitted from the Time of Sale Information and no statement of material fact included in the Time of Sale Information that is required to be included in the Prospectus has been omitted therefrom.

     (c) Issuer Free Writing Prospectus. Other than the Preliminary Prospectus and the Prospectus, the Company (including its agents and representatives) has not made, used, prepared, authorized, approved or referred to and will not prepare, make, use, authorize, approve or refer to any “written communication” (as defined in Rule 405 under the Securities Act) that constitutes an offer to sell or solicitation of an offer to buy the Shares (each such communication by the Company or its agents and representatives (other than a communication referred to in clause (i) below) an “Issuer Free Writing Prospectus”) other than (i) any document not constituting a prospectus pursuant to Section 2(a)(10)(a) of the Securities Act or Rule 134 under the Securities Act or (ii) the documents listed on Annex C hereto and other written communications approved in writing in advance by the Representatives. Each such Issuer Free Writing Prospectus complied in all material respects with the Securities Act, has been filed in accordance with the Securities Act (to the extent required thereby) and, when taken together with the Preliminary Prospectus accompanying, or delivered prior to delivery of, such Issuer Free Writing Prospectus, did not, and at the Closing Date and as of the Additional Closing Date, as the case may be, will not, contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in each such Issuer Free Writing Prospectus in reliance upon and in conformity with information relating to any Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for use in any Issuer Free Writing Prospectus.

     (d) Registration Statement and Prospectus. The Registration Statement has been declared effective by the Commission. No order suspending the effectiveness of the Registration Statement has been issued by the Commission and no proceeding for that purpose or pursuant to Section 8A of the Securities Act against the Company or related to the offering has been initiated or threatened by the Commission; as of the applicable effective date of the Registration Statement and any amendment thereto, the Registration Statement complied and will comply in all material respects with the Securities Act, and did not and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading; and as of the date of the Prospectus and any amendment or supplement thereto and as of the Closing Date and as of the Additional Closing Date, as the case may be, the Prospectus will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided that the Company makes no representation and warranty with respect to any statements or omissions made in reliance upon and in conformity with information relating to any Underwriter furnished to the

Company in writing by such Underwriter through the Representatives expressly for use in the Registration Statement and the Prospectus and any amendment or supplement thereto.

     (e) Financial Statements. (i) The financial statements and the related notes thereto of the Company and its consolidated subsidiaries included in the Registration Statement, the Time of Sale Information and the Prospectus comply in all material respects with the applicable requirements of the Securities Act and the Securities Exchange Act of 1934, as amended, and the rules and regulations of the Commission thereunder (collectively, the “Exchange Act”), as applicable, except to the extent relief therefrom has been granted in writing by the Staff of the SEC and present fairly in all material respects the financial position of the Company and its subsidiaries as of the dates indicated and the results of their operations and the changes in their cash flows for the periods specified; such financial statements have been prepared in conformity with generally accepted accounting principles applied on a consistent basis throughout the periods covered thereby, and the supporting schedules included in the Registration Statement present fairly in all material respects the information required to be stated therein; the other financial information included in the Registration Statement, the Time of Sale Information and the Prospectus has been derived from the accounting records of the Company and its subsidiaries and presents fairly in all material respects the information shown thereby; and the pro forma financial information and the related notes thereto included in the Registration Statement, the Time of Sale Information and the Prospectus have been prepared in all material respects consistently with the applicable requirements of the Securities Act and the Exchange Act, as applicable, and give effect to assumptions made on a reasonable basis as set forth in the Registration Statement, the Time of Sale Information and the Prospectus;

     (ii) The statements of revenue and direct operating expenses and the related notes thereto of the Lowe Properties included in the Registration Statement, the Time of Sale Information and the Prospectus comply in all material respects with the applicable requirements of the Securities Act and the Exchange Act, as applicable, and present fairly in all material respects the revenues and direct operating expenses of the Lowe Properties for the periods specified; such financial statements have been prepared in conformity with generally accepted accounting principles applied on a consistent basis throughout the periods covered thereby; the other financial information included in the Registration Statement, the Time of Sale Information and the Prospectus of the Lowe Properties has been derived from the accounting records of the Lowe Properties and presents fairly in all material respects the information shown thereby; and

     (iii) The financial statements and the related notes thereto of the Chase Group Properties included in the Registration Statement, the Time of Sale Information and the Prospectus (and as defined therein) comply in all material respects with the applicable requirements of the Securities Act and the Exchange Act, as applicable, and present fairly in all material respects the financial position of the Chase Group Properties as of the dates indicated and the results of their operations and the changes in their cash flows for the periods specified; such financial statements have been prepared in conformity with generally accepted accounting principles applied on a consistent basis throughout the periods covered thereby, the other financial information of the Chase Group Properties included in the Registration Statement, the Time of Sale Information and the Prospectus has been derived from the accounting records of the Chase Group Properties and presents fairly in all material respects the information shown thereby.

     (f) No Material Adverse Change. Since the date of the most recent financial statements of the Company included in the Registration Statement, the Time of Sale Information and the Prospectus, except in each case as otherwise disclosed in the Registration Statement, the Time of Sale Information and the Prospectus, (i) there has not been any change in the capital stock or material change in the long-term debt of the Company or any of its subsidiaries, or any dividend or distribution of any kind declared, set aside for payment, paid or made by the Company on any class of capital stock, or any material adverse

change, or any development involving a prospective material adverse change, in or affecting the business, properties, management, financial position, stockholders’ equity, results of operations or prospects of the Company and its subsidiaries taken as a whole; (ii) neither the Company nor any of its subsidiaries has entered into any transaction or agreement that is material to the Company and its subsidiaries taken as a whole or incurred any liability or obligation, direct or contingent, that is material to the Company and its subsidiaries taken as a whole; and (iii) neither the Company nor any of its subsidiaries has sustained any material loss or interference with its business from fire, explosion, flood or other calamity, whether or not covered by insurance, or from any labor disturbance or dispute or any action, order or decree of any court or arbitrator or governmental or regulatory authority, except in each case as otherwise disclosed in the Registration Statement, the Time of Sale Information and the Prospectus.

     (g) Organization and Good Standing. The Company and each of its subsidiaries have been duly organized and are validly existing and in good standing under the laws of their respective jurisdictions of organization, are duly qualified to do business and are in good standing in each jurisdiction in which their respective ownership or lease of property or the conduct of their respective businesses requires such qualification, and have all power and authority necessary to own or hold their respective properties and to conduct the businesses in which they are engaged, except where the failure to be so qualified or have such power or authority would not, individually or in the aggregate, have a material adverse effect on the business, properties, management, financial position, stockholders’ equity, results of operations, cash flows or prospects of the Company and its subsidiaries taken as a whole (a “Material Adverse Effect”). The Company does not own or control, directly or indirectly, any corporation, association or other entity other than the subsidiaries listed in Exhibit 21.1 to the Registration Statement.

     (h) Capitalization. The Company has authorized capital stock as set forth in the Registration Statement, the Time of Sale Information and the Prospectus under the heading “Description of capital stock”; all the outstanding shares of capital stock of the Company have been duly and validly authorized and issued and are fully paid and non-assessable and are not subject to any pre-emptive or similar rights; except as described in or expressly contemplated by the Time of Sale Information and the Prospectus, there are no outstanding rights (including, without limitation, pre-emptive rights), warrants or options to acquire, or instruments convertible into or exchangeable for, any shares of capital stock or other equity interest in the Company or any of its subsidiaries, or any contract, commitment, agreement, understanding or arrangement of any kind relating to the issuance of any capital stock of the Company or any such subsidiary, any such convertible or exchangeable securities or any such rights, warrants or options; the capital stock of the Company conforms in all material respects to the description thereof contained in the Registration Statement, the Time of Sale Information and the Prospectus; and all the outstanding shares of capital stock or other equity interests of each subsidiary of the Company have been duly and validly authorized and issued, are fully paid and non-assessable (except as otherwise described in the Registration Statement, the Time of Sale Information and the Prospectus) and are owned directly or indirectly by the Company, free and clear of any lien, charge, encumbrance, security interest, restriction on voting or transfer or any other claim of any third party, other than those arising under the Company’s Credit Agreement dated February 24, 2006 and Second Lien Credit Agreement dated March 27, 2007.

     (i) Due Authorization. The Company has full corporate, power and authority to execute and deliver this Agreement and to perform its obligations hereunder; and all corporate action required to be taken for the due and proper authorization, execution and delivery by it of this Agreement and the consummation by it of the transactions contemplated hereby has been duly and validly taken.

     (j) Underwriting Agreement. This Agreement has been duly authorized, executed and delivered by the Company.

     (k) The Shares. The Shares to be sold by the Selling Stockholders hereunder have been duly authorized by the Company and are fully paid, nonassessable and conform to the descriptions thereof in the Registration Statement, the Time of Sale Information and the Prospectus.

     (l) No Violation or Default. Neither the Company nor any of its subsidiaries is (i) in violation of its charter or by-laws or similar organizational documents; (ii) in default, and no event has occurred that, with notice or lapse of time or both, would constitute such a default, in the due performance or observance of any term, covenant or condition contained in any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which the Company or any of its subsidiaries is a party or by which the Company or any of its subsidiaries is bound or to which any of the property or assets of the Company or any of its subsidiaries is subject; or (iii) in violation of any law or statute or any judgment, order, rule or regulation of any court or arbitrator or governmental or regulatory authority, except, in the case of clauses (ii) and (iii) above, for any such default or violation that would not, individually or in the aggregate, have a Material Adverse Effect.

     (m) No Conflicts. The execution, delivery and performance by the Company of this Agreement and the consummation of the transactions contemplated by this Agreement will not (i) conflict with or result in a breach or violation of any of the terms or provisions of, or constitute a default under, or result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of the Company or any of its subsidiaries pursuant to, any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which the Company or any of its subsidiaries is a party or by which the Company or any of its subsidiaries is bound or to which any of the property or assets of the Company or any of its subsidiaries is subject, (ii) result in any violation of the provisions of the charter or by-laws or similar organizational documents of the Company or any of its subsidiaries or (iii) result in the violation of any law or statute or any judgment, order, rule or regulation of any court or arbitrator or governmental or regulatory authority, except, in the case of clauses (i) and (iii) above, for any such conflict, breach or violation that would not, individually or in the aggregate, have a Material Adverse Effect.

     (n) No Consents Required. No consent, approval, authorization, order, registration or qualification of or with any court or arbitrator or governmental or regulatory authority is required for the execution, delivery and performance by the Company of this Agreement and the consummation of the transactions contemplated by this Agreement, except for the registration of the Shares under the Securities Act and such consents, approvals, authorizations, orders and registrations or qualifications as may be required under applicable state securities laws in connection with the purchase and distribution of the Shares by the Underwriters and any consent, approval, authorization, order, registration or qualification that either has been, or prior to the Closing Date will have been, obtained or made, or which if not obtained or made, would not, individually or in the aggregate, have a Material Adverse Effect and would not adversely affect the Company’s ability to fulfill its obligations under this Agreement.

     (o) Legal Proceedings. Except as described in the Registration Statement, the Time of Sale Information and the Prospectus, there are no legal, governmental or regulatory investigations, actions, suits or proceedings pending to which the Company or any of its subsidiaries is or may be a party or to which any property of the Company or any of its subsidiaries is or may be the subject that, individually or in the aggregate, if determined adversely to the Company or any of its subsidiaries, could reasonably be expected to have a Material Adverse Effect or materially and adversely affect the ability of the Company to perform its obligations under this Agreement; to the knowledge of the Company, no such investigations, actions, suits or proceedings are threatened or contemplated by any governmental or regulatory authority or others; and (i) there are no current or pending legal, governmental or regulatory actions, suits or proceedings that are required under the Securities Act to be described in the Registration Statement that are not so described in the Registration Statement, the Time of Sale Information and the Prospectus and

(ii) there are no statutes, regulations or contracts or other documents that are required under the Securities Act to be filed as exhibits to the Registration Statement or described in the Registration Statement or the Prospectus that are not so filed as exhibits to the Registration Statement or described in the Registration Statement, the Time of Sale Information and the Prospectus.

     (p) Independent Accountants. Grant Thornton LLP, who has certified certain financial statements of the Company and its subsidiaries, is an independent registered public accounting firm with respect to the Company and its subsidiaries within the applicable rules and regulations adopted by the Commission and the Public Company Accounting Oversight Board (United States) and as required by the Securities Act.

     (q) Title to Real and Personal Property. The Company and its subsidiaries have good and marketable title to all real and other property they own, in each case free and clear of all liens, encumbrances and defects except those (i) described in the Registration Statement, the Time of Sale Information and the Prospectus or (ii) that could not reasonably be expected, individually or in the aggregate, to have a Material Adverse Effect. Except as described in the Registration Statement, the Time of Sale Information and the Prospectus, all items of real and other property leased by the Company and its subsidiaries are leased under valid and enforceable leases, except as could not reasonably be expected, individually or in the aggregate, to have a Material Adverse Effect.

     (r) Title to Intellectual Property. The Company and its subsidiaries own or possess adequate rights to use any and all material patents, patent applications, trademarks, service marks, trade names, trademark registrations, service mark registrations, copyrights, licenses and know-how (including trade secrets and other unpatented and/or unpatentable proprietary or confidential information, systems or procedures) necessary for the conduct of their respective businesses, and the Company and its subsidiaries have not received any notice of any claim of infringement or conflict with any such rights of others.

     (s) No Undisclosed Relationships. No relationship, direct or indirect, exists between or among the Company or any of its subsidiaries, on the one hand, and the directors, officers, stockholders, customers or suppliers of the Company or any of its subsidiaries, on the other, that is required by the Securities Act to be described in the Registration Statement and the Prospectus and that is not so described in such documents and in the Time of Sale Information.

     (t) Investment Company Act. The Company is not required to register as an “investment company” or an entity “controlled” by an “investment company” within the meaning of the Investment Company Act of 1940, as amended, and the rules and regulations of the Commission thereunder (collectively, “Investment Company Act”).

     (u) Taxes. The Company and its subsidiaries have paid all federal, state, local and foreign taxes and filed all tax returns required to be paid or filed through the date hereof; and except as otherwise disclosed in the Registration Statement, the Time of Sale Information and the Prospectus or as would not, individually or in the aggregate, have a Material Adverse Effect, there is no tax deficiency that has been, or could reasonably be expected to be, asserted against the Company or any of its subsidiaries or any of their respective properties or assets.

     (v) Licenses and Permits. The Company and its subsidiaries possess all licenses, certificates, permits and other authorizations issued by, and have made all declarations and filings with, the appropriate federal, state, local or foreign governmental or regulatory authorities that are necessary for the ownership or lease of their respective properties or the conduct of their respective businesses as described in the Registration Statement, the Time of Sale Information and the Prospectus, except where the failure to possess or make the same would not, individually or in the aggregate, have a Material Adverse Effect; and

except as described in the Registration Statement, the Time of Sale Information and the Prospectus or as would not, individually or in the aggregate, have a Material Adverse Effect, neither the Company nor any of its subsidiaries has received notice of any revocation or modification of any such license, certificate, permit or authorization or has any reason to believe that any such license, certificate, permit or authorization will not be renewed in the ordinary course.

     (w) No Labor Disputes. No labor disturbance by or dispute with employees of the Company or any of its subsidiaries exists or, to the knowledge of the Company, is contemplated or threatened and the Company is not aware of any existing or imminent labor disturbance by, or dispute with, the employees of any of its or its subsidiaries’ principal suppliers, contractors or customers, except as would not have a Material Adverse Effect.

     (x) Compliance With Environmental Laws. (i) The Company and its subsidiaries (x) are in compliance with any and all applicable federal, state, local and foreign laws, rules, regulations, requirements, decisions and orders relating to the protection of human health and safety, the environment or hazardous or toxic substances or wastes, pollutants or contaminants (collectively, “Environmental Laws”); (y) have received and are in compliance with all permits, licenses, certificates or other authorizations or approvals required of them under applicable Environmental Laws to conduct their respective businesses; and (z) except as described in the Registration Statement, the Time of Sale Information and the Prospectus, have not received notice of any actual or potential liability for the investigation or remediation of any disposal or release of hazardous or toxic substances or wastes, pollutants or contaminants, and (ii) there are no costs or liabilities associated with Environmental Laws of or relating to the Company or its subsidiaries, except in the case of each of (i) and (ii) above, for any such failure to comply, or failure to receive required permits, licenses or approvals, or cost or liability, as would not, individually or in the aggregate, have a Material Adverse Effect.

     (y) Compliance With ERISA. Each employee benefit plan, within the meaning of Section 3(3) of the Employee Retirement Income Security Act of 1974, as amended (“ERISA”), that is maintained, administered or contributed to by the Company or any of its affiliates for employees or former employees of the Company and its affiliates has been maintained in compliance in all material respects with its terms and the requirements of any applicable statutes, orders, rules and regulations, including, but not limited to, ERISA and the Internal Revenue Code of 1986, as amended (the “Code”); no prohibited transaction, within the meaning of Section 406 of ERISA or Section 4975 of the Code, has occurred with respect to any such plan excluding transactions effected pursuant to a statutory or administrative exemption; and transactions which, individually or in the aggregate, would not have a Material Adverse Effect, and no such plan is subject to the funding rules of Section 412 of the Code or Section 302 of ERISA.

     (z) Disclosure Controls. The Company and its subsidiaries maintain an effective system of “disclosure controls and procedures” (as defined in Rule 13a-15(e) of the Exchange Act) that is designed to ensure that information which will be required to be disclosed by the Company in reports that it files or submits under the Exchange Act will be recorded, processed, summarized and reported within the time periods specified in the Commission’s rules and forms, including controls and procedures designed to ensure that such information will be accumulated and communicated to the Company’s management as appropriate to allow timely decisions regarding required disclosure.

     (aa) Accounting Controls. The Company and its subsidiaries maintain a system of “internal control over financial reporting” (as defined in Rule 13a-15(f) of the Exchange Act) that comply with the requirements of the Exchange Act and have been designed by, or under the supervision of, the Company’s principal executive and principal financial officers, and effected by the Company’s board of directors, management and other personnel to provide reasonable assurance regarding the reliability of financial

reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles, including those policies and procedures that (i) pertain to the maintenance of records that in reasonable detail accurately and fairly reflect the transactions and dispositions of the assets of the Company; (ii) provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles and that receipts and expenditures of the Company are being made in accordance with and authorizations of management and directors of the Company; and (iii) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use or disposition of the Company’s assets that could have a material effect on the Company’s financial statements. Except as disclosed in the Registration Statement, the Time of Sale Information and the Prospectus, there are no material weaknesses in the Company’s internal control over financial reporting.

     (bb) Insurance. The Company and its subsidiaries have insurance covering their respective properties, operations, personnel and businesses, which insurance is in reasonable amounts and insures against such losses and risks as are reasonably adequate to protect the Company and its subsidiaries and their respective businesses; and neither the Company nor any of its subsidiaries has (i) received notice from any insurer or agent of such insurer that capital improvements or other expenditures are required or necessary to be made in order to continue such insurance or (ii) any reason to believe that it will not be able to renew its existing insurance coverage as and when such coverage expires or to obtain similar coverage at reasonable cost from similar insurers as may be necessary to continue its business.

     (cc) No Unlawful Payments. Neither the Company nor any of its subsidiaries nor, to the knowledge of the Company, any director, officer, agent, employee or other person associated with or acting on behalf of the Company or any of its subsidiaries has (i) used any corporate funds for any unlawful contribution, gift, entertainment or other unlawful expense relating to political activity; (ii) made any direct or indirect unlawful payment to any foreign or domestic government official or employee from corporate funds; (iii) violated or is in violation of any provision of the Foreign Corrupt Practices Act of 1977; or (iv) made any bribe, rebate, payoff, influence payment, kickback or other unlawful payment.

     (dd) Compliance with Money Laundering Laws. The operations of the Company and its subsidiaries are and have been conducted at all times in compliance with applicable financial recordkeeping and reporting requirements of the Currency and Foreign Transactions Reporting Act of 1970, as amended, the money laundering statutes of all jurisdictions, the rules and regulations thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any governmental agency (collectively, the “Money Laundering Laws”) and no action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Company or any of its subsidiaries with respect to the Money Laundering Laws is pending or, to the knowledge of the Company, threatened.

     (ee) Compliance with OFAC. None of the Company, any of its subsidiaries or, to the knowledge of the Company, any director, officer, agent, employee or Affiliate of the Company or any of its subsidiaries is currently subject to any U.S. sanctions administered by the Office of Foreign Assets Control of the U.S. Department of the Treasury (“OFAC”).

     (ff) No Restrictions on Subsidiaries. No subsidiary of the Company is currently prohibited, directly or indirectly, under any agreement or other instrument to which it is a party or is subject, from paying any dividends to the Company, from making any other distribution on such subsidiary’s capital stock, from repaying to the Company any loans or advances to such subsidiary from the Company or from transferring any of such subsidiary’s properties or assets to the Company or any other subsidiary of the Company.

     (gg) No Broker’s Fees. Neither the Company nor any of its subsidiaries is a party to any contract, agreement or understanding with any person (other than this Agreement) that would give rise to a valid claim against the Company or any of its subsidiaries or any Underwriter for a brokerage commission, finder’s fee or like payment in connection with the offering and sale of the Shares.

     (hh) No Registration Rights. Except as disclosed in the Registration Statement, the Time of Sale Information and the Prospectus, no person has the right to require the Company or any of its subsidiaries to register any securities for sale under the Securities Act by reason of the filing of the Registration Statement with the Commission or the issuance and sale of the Shares.

     (ii) No Stabilization. The Company has not taken, directly or indirectly, any action designed to or that could reasonably be expected to cause or result in any stabilization or manipulation of the price of the Shares.

     (jj) Forward-Looking Statements. No forward-looking statement (within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act) contained in the Registration Statement, the Time of Sale Information and the Prospectus has been made or reaffirmed without a reasonable basis or has been disclosed other than in good faith.

     (kk) Statistical and Market Data. Nothing has come to the attention of the Company that has caused the Company to believe that the statistical and market-related data included in the Registration Statement, the Time of Sale Information and the Prospectus is not based on or derived from sources that are reliable and accurate in all material respects.

     (ll) Sarbanes-Oxley Act. There is and has been no failure on the part of the Company or any of the Company’s directors or officers, in their capacities as such, to comply with any applicable provision of the Sarbanes-Oxley Act of 2002 and any applicable rules and regulations promulgated in connection therewith (the “Sarbanes-Oxley Act”), including Section 402 related to loans.

     (mm) Status under the Securities Act. The Company is not an ineligible issuer as defined under the Securities Act, at the times specified in the Securities Act in connection with the offering of the Shares.

     (nn) Reserve Data. (i) The oil and natural gas reserve estimates of the Company and its subsidiaries as of December 31, 2004, 2005 and 2006 contained in the Registration Statement, the Time of Sale Information and the Prospectus are derived from reports that have been prepared by, or have been audited by, either (a) Netherland, Sewell & Associates, Inc. or (b) Cawley, Gillespie & Associates, Inc., as set forth and to the extent indicated therein, and such estimates fairly reflect the oil and natural gas reserves of the Company and its subsidiaries, as applicable, at the dates indicated therein and are in accordance, in all material respects, with Commission guidelines applied on a consistent basis throughout the periods involved; and

     (ii) The oil and natural gas reserve estimates of the Chase Group Properties as of December 31, 2003, 2004 and 2005 contained in the Registration Statement, the Time of Sale Information and the Prospectus are derived from reports that have been prepared by, or have been audited by Cawley, Gillespie & Associates, Inc., as set forth therein, and such estimates fairly reflect the oil and natural gas reserves of the Chase Group Properties, at the dates indicated therein and are in accordance, in all material respects, with Commission guidelines applied on a consistent basis throughout the periods involved.

     (oo) Independent Petroleum Engineers. Each of Netherland, Sewell & Associates, Inc. and Cawley, Gillespie & Associates, Inc. have represented to the Company that they are, and the Company

believes them to be, independent petroleum engineers with respect to the Company and its subsidiaries and for the periods set forth in the Registration Statement, the Time of Sale Information and the Prospectus.

     4. Representations and Warranties of the Selling Stockholders. (i) The Chase Stockholders represent and warrant, jointly and severally, to each Underwriter and the Company that:

     (a) Required Consents; Authority. All consents, approvals, authorizations and orders necessary for the execution and delivery by such Chase Stockholder of this Agreement and the Power of Attorney (the “Power of Attorney”) and the Custody Agreement (the “Custody Agreement”) hereinafter referred to, and for the sale and delivery of the Shares to be sold by such Chase Stockholder hereunder, have been obtained; and such Chase Stockholder has full right, power and authority to enter into this Agreement, the Power of Attorney and the Custody Agreement and to sell, assign, transfer and deliver the Shares to be sold by such Chase Stockholder hereunder; this Agreement, the Power of Attorney and the Custody Agreement have each been duly authorized, executed and delivered by such Chase Stockholder.

     (b) No Conflicts. The execution, delivery and performance by such Chase Stockholder of this Agreement, the Power of Attorney and the Custody Agreement, the sale of the Shares to be sold by such Chase Stockholder and the consummation by such Chase Stockholder of the transactions herein and therein contemplated will not (i) conflict with or result in a breach or violation of any of the terms or provisions of, or constitute a default under, or result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of such Chase Stockholder pursuant to, any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which such Chase Stockholder is a party or by which such Chase Stockholder is bound or to which any of the property or assets of such Chase Stockholder is subject, (ii) result in any violation of the provisions of the charter or by-laws or similar organizational documents of such Chase Stockholder or (iii) result in the violation of any law or statute or any judgment, order, rule or regulation of any court or arbitrator or governmental or regulatory agency.

     (c) Title to Shares. Such Chase Stockholder has good and valid title to the Shares to be sold at the Closing Date or the Additional Closing Date, as the case may be, by such Chase Stockholder hereunder, free and clear of all liens, encumbrances, equities or adverse claims; such Chase Stockholder will have, immediately prior to the Closing Date or the Additional Closing Date, as the case may be, good and valid title to the Shares to be sold at the Closing Date or the Additional Closing Date, as the case may be, by such Chase Stockholder, free and clear of all liens, encumbrances, equities or adverse claims; and, upon delivery of the certificates representing such Shares and payment therefor pursuant hereto, good and valid title to such Shares, free and clear of all liens, encumbrances, equities or adverse claims, will pass to the several Underwriters.

     (d) No Stabilization. Such Chase Stockholder has not taken and will not take, directly or indirectly, any action designed to or that could reasonably be expected to cause or result in any stabilization or manipulation of the price of the Shares.

     (e) Time of Sale Information. The Time of Sale Information, at the Time of Sale did not, and at the Closing Date and as of the Additional Closing Date, as the case may be, will not, contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that the representations and warranties set forth in this paragraph are limited to statements or omissions made in reliance upon information relating to Chase Oil Corporation, Caza Energy LLC, their stockholders and affiliates (other than the Company and its subsidiaries), the Chase Group Properties and the Chase Group Properties financial statements (collectively, the “Time of Sale Chase Information”).

     (f) Issuer Free Writing Prospectus. Other than the Preliminary Prospectus and the Prospectus, such Chase Stockholder (including its agents and representatives) has not made, used, prepared, authorized, approved or referred to and will not prepare, make, use, authorize, approve or refer to any Issuer Free Writing Prospectus, other than (i) any document not constituting a prospectus pursuant to Section 2(a)(10)(a) of the Securities Act or Rule 134 under the Securities Act or (ii) the documents listed on Annex C hereto and other written communications approved in writing in advance by the Company and the Representatives.

     (g) Registration Statement and Prospectus. As of the applicable effective date of the Registration Statement and any amendment thereto, the Registration Statement complied and will comply in all material respects with the Securities Act, and did not and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading; and as of the date of the Prospectus and any amendment or supplement thereto and as of the Closing Date and as of the Additional Closing Date, as the case may be, the Prospectus will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that the representations and warranties set forth in this paragraph are limited to information contained in the Registration Statement, Prospectus (or any amendment or supplement thereto) or any Issuer Free Writing Prospectus relating to Chase Oil Corporation, Caza Energy LLC, their stockholders and affiliates, the Chase Group Properties and the Chase Group Properties financial statements included in the Prospectus (collectively, the “Registration Statement Chase Information,” and together with the Time of Sale Chase Information, the “Chase Information”).

     (h) Material Information. As of the date hereof, as of the Closing Date and as of the Additional Closing Date, as the case may be, the sale of the Shares by such Chase Stockholder is not and will not be prompted by any material information concerning the Company which is not set forth in the Registration Statement, the Time of Sale Information or the Prospectus.

     (ii) Each Chase Stockholder represents and warrants to each Underwriter and the Company that certificates in negotiable form representing all of the Shares to be sold by such Chase Stockholder hereunder have been placed in custody under a Custody Agreement relating to such Shares, in the form heretofore furnished to you, duly executed and delivered by such Chase Stockholder to American Stock Transfer & Trust Company, as custodian (the “Custodian”), and that such Chase Stockholder has duly executed and delivered a Power of Attorney, in the form heretofore furnished to you, appointing the person or persons indicated in Schedule 4 hereto, and each of them, as such Chase Stockholder’s Attorneys-in-fact (the “Chase Attorneys-in-Fact” or any one of them, the “Chase Attorney-in-Fact”) with authority to execute and deliver this Agreement on behalf of such Chase Stockholder, to determine the purchase price to be paid by the Underwriters to the Chase Stockholders as provided herein, to authorize the delivery of the Shares to be sold by such Chase Stockholder hereunder and otherwise to act on behalf of such Chase Stockholder in connection with the transactions contemplated by this Agreement and the Custody Agreement.

     (iii) Each Chase Stockholder specifically agrees that the Shares represented by the certificates held in custody for such Chase Stockholder under the Custody Agreement are subject to the interests of the Underwriters hereunder, and that the arrangements made by such Chase Stockholder for such custody, and the appointment by such Chase Stockholder of the Chase Attorneys-in-Fact by the Power of Attorney, are to that extent irrevocable. Each Chase Stockholder specifically agrees that the obligations of such Chase Stockholder hereunder shall not be terminated by operation of law, whether by the death or incapacity of any individual Chase Stockholder, or, in the case of an estate or trust, by the death or

incapacity of any executor or trustee or the termination of such estate or trust, or in the case of a partnership, corporation or similar organization, by the dissolution of such partnership, corporation or organization, or by the occurrence of any other event. If any individual Chase Stockholder or any such executor or trustee should die or become incapacitated, or if any such estate or trust should be terminated, or if any such partnership, corporation or similar organization should be dissolved, or if any other such event should occur, before the delivery of the Shares hereunder, certificates representing such Shares shall be delivered by or on behalf of such Chase Stockholder in accordance with the terms and conditions of this Agreement and the Custody Agreement, and actions taken by the Chase Attorneys-in-Fact pursuant to the Powers of Attorney shall be as valid as if such death, incapacity, termination, dissolution or other event had not occurred, regardless of whether or not the Custodian, the Chase Attorneys-in-Fact, or any of them, shall have received notice of such death, incapacity, termination, dissolution or other event.

     (iv) Each Non-Chase Stockholder represents and warrants severally and not jointly to each Underwriter and the Company that:

     (a) Required Consents; Authority. All consents, approvals, authorizations and orders necessary for the execution and delivery by such Non-Chase Stockholder of this Agreement and the Power of Attorney (the “Power of Attorney”) and the Custody Agreement (the “Custody Agreement”) hereinafter referred to, and for the sale and delivery of the Shares to be sold by such Non-Chase Stockholder hereunder, have been obtained; and such Non-Chase Stockholder has full right, power and authority to enter into this Agreement, the Power of Attorney and the Custody Agreement and to sell, assign, transfer and deliver the Shares to be sold by such Non-Chase Stockholder hereunder; this Agreement, the Power of Attorney and the Custody Agreement have each been duly authorized, executed and delivered by such Non-Chase Stockholder.

     (b) No Conflicts. The execution, delivery and performance by such Non-Chase Stockholder of this Agreement, the Power of Attorney and the Custody Agreement, the sale of the Shares to be sold by such Non-Chase Stockholder and the consummation by such Non-Chase Stockholder of the transactions herein and therein contemplated will not (i) conflict with or result in a breach or violation of any of the terms or provisions of, or constitute a default under, or result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of such Non-Chase Stockholder pursuant to, any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which such Non-Chase Stockholder is a party or by which such Non-Chase Stockholder is bound or to which any of the property or assets of such Non-Chase Stockholder is subject or (ii) result in the violation of any law or statute or any judgment, order, rule or regulation of any court or arbitrator or governmental or regulatory agency applicable to such Non-Chase Stockholder, except, in the case of clauses (i) and (ii) above, for any such conflict, breach or violation that would not, individually or in the aggregate, have a Material Adverse Effect.

     (c) Title to Shares. Such Non-Chase Stockholder has good and valid title to the Shares to be sold at the Closing Date or the Additional Closing Date, as the case may be, by such Non-Chase Stockholder hereunder, free and clear of all liens, encumbrances, equities or adverse claims; such Non-Chase Stockholder will have, immediately prior to the Closing Date or the Additional Closing Date, as the case may be, good and valid title to the Shares to be sold at the Closing Date or the Additional Closing Date, as the case may be, by such Non-Chase Stockholder, free and clear of all liens, encumbrances, equities or adverse claims; and, upon delivery of the certificates representing such Shares and payment therefor pursuant hereto, good and valid title to such Shares, free and clear of all liens, encumbrances, equities or adverse claims, will pass to the several Underwriters.

     (d) No Stabilization. Such Non-Chase Stockholder has not taken and will not take, directly or indirectly, any action designed to or that could reasonably be expected to cause or result in any stabilization or manipulation of the price of the Shares.

     (e) Time of Sale Information. The Time of Sale Information, at the Time of Sale did not, and at the Closing Date and as of the Additional Closing Date, as the case may be, will not, contain any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that the representations and warranties set forth in this paragraph are limited to statements or omissions made in reliance upon information relating to such Non-Chase Stockholder furnished to the Company in writing by such Non-Chase Stockholder expressly for use in the Time of Sale Information (the “ Non-Chase Stockholder Time of Sale Information”).

     (f) Issuer Free Writing Prospectus. Other than the Preliminary Prospectus and the Prospectus, such Non-Chase Stockholder (including its agents and representatives, other than the Underwriters in their capacity as such) has not made, used, prepared, authorized, approved or referred to and will not prepare, make, use, authorize, approve or refer to any Issuer Free Writing Prospectus, other than (i) any document not constituting a prospectus pursuant to Section 2(a)(10)(a) of the Securities Act or Rule 134 under the Securities Act or (ii) the documents listed on Annex C hereto and other written communications approved in writing in advance by the Company and the Representatives.

     (g) Registration Statement and Prospectus. As of the applicable effective date of the Registration Statement and any amendment thereto, the Registration Statement complied and will comply in all material respects with the Securities Act, and did not and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading; and as of the date of the Prospectus and any amendment or supplement thereto and as of the Closing Date and as of the Additional Closing Date, as the case may be, the Prospectus will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading; provided, however, that the representations and warranties set forth in this paragraph are limited to statements or omissions made in reliance upon information relating to such Non-Chase Stockholder furnished to the Company in writing by such Non-Chase Stockholder expressly for the use in the Registration Statement, Prospectus (or any amendment or supplement thereto) or any Issuer Free Writing Prospectus (the “Non-Chase Stockholder Registration Statement Information”, and together with the Non-Chase Stockholder Time of Sale Information, the “Non-Chase Stockholder Information”).

     (h) Material Information. As of the date hereof, as of the Closing Date and as of the Additional Closing Date, as the case may be, the sale of the Shares by such Non-Chase Stockholder is not and will not be prompted by any material information concerning the Company which is not set forth in the Registration Statement, the Time of Sale Information or the Prospectus.

     (v) Each Non-Chase Stockholder represents and warrants to each Underwriter and the Company that certificates in negotiable form representing all of the Shares to be sold by such Non-Chase Stockholder hereunder have been placed in custody under a Custody Agreement relating to such Shares, in the form heretofore furnished to you, duly executed and delivered by such Non-Chase Stockholder to American Stock Transfer & Trust Company, as custodian (the “Custodian”), and that such Non-Chase Stockholder has duly executed and delivered a Power of Attorney, in the form heretofore furnished to you, appointing the person or persons indicated in Schedule 5 hereto, and each of them, as such Non-Chase Stockholder’s Attorneys-in-fact (the “Non-Chase Attorneys-in-Fact” or any one of them the “Non-

Chase Attorney-in Fact”) with authority to execute and deliver this Agreement on behalf of such Non-Chase Stockholder, to determine the purchase price to be paid by the Underwriters to the Non-Chase Stockholders as provided herein, to authorize the delivery of the Shares to be sold by such Non-Chase Stockholder hereunder and otherwise to act on behalf of such Non-Chase Stockholder in connection with the transactions contemplated by this Agreement and the Custody Agreement.

     (vi) Each Non-Chase Stockholder specifically agrees that the Shares represented by the certificates held in custody for such Non-Chase Stockholder under the Custody Agreement are subject to the interests of the Underwriters hereunder, and that the arrangements made by such Non-Chase Stockholder for such custody, and the appointment by such Non-Chase Stockholder of the Non-Chase Attorneys-in-Fact by the Power of Attorney, are to that extent irrevocable. Each Non-Chase Stockholder specifically agrees that the obligations of such Non-Chase Stockholder hereunder shall not be terminated by operation of law, whether by the death or incapacity of any individual Non-Chase Stockholder, or, in the case of an estate or trust, by the death or incapacity of any executor or trustee or the termination of such estate or trust, or in the case of a partnership, corporation or similar organization, by the dissolution of such partnership, corporation or organization, or by the occurrence of any other event. If any individual Non-Chase Stockholder or any such executor or trustee should die or become incapacitated, or if any such estate or trust should be terminated, or if any such partnership, corporation or similar organization should be dissolved, or if any other such event should occur, before the delivery of the Shares hereunder, certificates representing such Shares shall be delivered by or on behalf of such Non-Chase Stockholder in accordance with the terms and conditions of this Agreement and the Custody Agreement, and actions taken by the Non-Chase Attorneys-in-Fact pursuant to the Powers of Attorney shall be as valid as if such death, incapacity, termination, dissolution or other event had not occurred, regardless of whether or not the Custodian, the Non-Chase Attorneys-in-Fact, or any of them, shall have received notice of such death, incapacity, termination, dissolution or other event.

     5. Further Agreements of the Company. The Company covenants and agrees with each Underwriter and each Selling Stockholder that:

     (a) Required Filings. The Company will file the final Prospectus with the Commission within the time periods specified by Rule 424(b) and Rule 430A, 430B or 430C under the Securities Act, will file any Issuer Free Writing Prospectus to the extent required by Rule 433 under the Securities Act; and the Company will furnish copies of the Prospectus and each Issuer Free Writing Prospectus (to the extent not previously delivered) to the Underwriters in New York City prior to 10:00 A.M., New York City time, on the business day next succeeding the date of this Agreement in such quantities as the Representatives may reasonably request.

     (b) Delivery of Copies. The Company will deliver, without charge, (i) to the Representatives, three signed copies of the Registration Statement as originally filed and each amendment thereto, in each case including all exhibits and consents filed therewith; and (ii) to each Underwriter (A) a conformed copy of the Registration Statement as originally filed and each amendment thereto (without exhibits) and (B) during the Prospectus Delivery Period (as defined below), as many copies of the Prospectus (including all amendments and supplements thereto) and each Issuer Free Writing Prospectus as the Representatives may reasonably request. As used herein, the term “Prospectus Delivery Period” means such period of time after the first date of the public offering of the Shares as in the opinion of counsel for the Underwriters a prospectus relating to the Shares is required by law to be delivered (or required to be delivered but for Rule 172 under the Securities Act) in connection with sales of the Shares by any Underwriter or dealer.

     (c) Amendments or Supplements, Issuer Free Writing Prospectuses. Before preparing, using, authorizing, approving, referring to or filing any Issuer Free Writing Prospectus, and before filing any amendment or supplement to the Registration Statement or the Prospectus, the Company will furnish to the Representatives and counsel for the Underwriters a copy of the proposed Issuer Free Writing Prospectus, amendment or supplement for review and will not prepare, use, authorize, approve, refer to or file any such Issuer Free Writing Prospectus or file any such proposed amendment or supplement to which the Representatives reasonably object.

     (d) Notice to the Representatives. The Company will advise the Representatives promptly, and confirm such advice in writing, (i) when the Registration Statement has become effective; (ii) when any amendment to the Registration Statement has been filed or becomes effective; (iii) when any supplement to the Prospectus or any Issuer Free Writing Prospectus or any amendment to the Prospectus has been filed; (iv) of any request by the Commission for any amendment to the Registration Statement or any amendment or supplement to the Prospectus or the receipt of any comments from the Commission relating to the Registration Statement or any other request by the Commission for any additional information; (v) of the issuance by the Commission of any order suspending the effectiveness of the Registration Statement or preventing or suspending the use of any Preliminary Prospectus or the Prospectus or the initiation or threatening of any proceeding for that purpose or pursuant to Section 8A of the Securities Act; (vi) of the occurrence of any event within the Prospectus Delivery Period as a result of which the Prospectus, the Time of Sale Information or any Issuer Free Writing Prospectus as then amended or supplemented would include any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances existing when the Prospectus, the Time of Sale Information or any such Issuer Free Writing Prospectus is delivered to a purchaser, not misleading; and (vii) of the receipt by the Company of any notice with respect to any suspension of the qualification of the Shares for offer and sale in any jurisdiction or the initiation or threatening of any proceeding for such purpose; and the Company will use its best efforts to prevent the issuance of any such order suspending the effectiveness of the Registration Statement, preventing or suspending the use of any Preliminary Prospectus or the Prospectus or suspending any such qualification of the Shares and, if any such order is issued, will obtain as soon as possible the withdrawal thereof.

     (e) Ongoing Compliance. (1) If during the Prospectus Delivery Period (i) any event shall occur or condition shall exist as a result of which the Prospectus as then amended or supplemented would include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances existing when the Prospectus is delivered to a purchaser, not misleading or (ii) it is necessary to amend or supplement the Prospectus to comply with law, the Company will immediately notify the Underwriters thereof and forthwith prepare and, subject to paragraph (c) above, file with the Commission and furnish to the Underwriters and to such dealers as the Representatives may designate, such amendments or supplements to the Prospectus as may be necessary so that the statements in the Prospectus as so amended or supplemented will not, in the light of the circumstances existing when the Prospectus is delivered to a purchaser, be misleading or so that the Prospectus will comply with law and (2) if at any time prior to the Closing Date (i) any event shall occur or condition shall exist as a result of which the Time of Sale Information as then amended or supplemented would include any untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in the light of the circumstances, not misleading or (ii) it is necessary to amend or supplement the Time of Sale Information to comply with law, the Company will immediately notify the Underwriters thereof and forthwith prepare and, subject to paragraph (c) above, file with the Commission (to the extent required) and furnish to the Underwriters and to such dealers as the Representatives may designate, such amendments or supplements to the Time of Sale Information as may be necessary so that the statements in the Time of Sale Information as so

amended or supplemented will not, in the light of the circumstances, be misleading or so that the Time of Sale Information will comply with law.

     (f) Blue Sky Compliance. The Company will qualify the Shares for offer and sale under the securities or Blue Sky laws of such jurisdictions as the Representatives shall reasonably request and will continue such qualifications in effect so long as required for distribution of the Shares; provided that the Company shall not be required to (i) qualify as a foreign corporation or other entity or as a dealer in securities in any such jurisdiction which it would not otherwise be required to so qualify, (ii) file any general consent to service of process in any such jurisdiction or (iii) subject itself to taxation in any such jurisdiction if it is not otherwise so subject.

     (g) Earning Statement. The Company will make generally available to its security holders and the Representatives as soon as practicable an earning statement that satisfies the provisions of Section 11(a) of the Securities Act and Rule 158 of the Commission promulgated thereunder covering a period of at least twelve months beginning with the first fiscal quarter of the Company occurring after the “effective date” (as defined in Rule 158) of the Registration Statement.

     (h) Clear Market. For a period of 90 days after the date of the Prospectus, the Company will not (i) offer, pledge, announce the intention to sell, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase or otherwise transfer or dispose of, directly or indirectly, any shares of Stock or any securities convertible into or exercisable or exchangeable for Stock or (ii) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Stock or such other securities, in cash or otherwise, without the prior written consent of the Representatives, other than (A) the Shares to be sold hereunder, (B) any shares of Stock of the Company issued upon the exercise of options granted under existing employee stock option plans; provided, however, that once issued, each distributee shall execute and deliver to the Representatives a lock-up letter in the form of this paragraph, (C) grants by the Company of any employee stock options or restricted stock in accordance with the terms of the 2006 Stock Incentive Plan as in effect on the date hereof (the “Plan”) and (D) the filing by the Company of any registration statement with the Commission on Form S-8 relating to the offering of securities pursuant to the terms of the Plan. Notwithstanding the foregoing, if (1) during the last 17 days of the 90-day restricted period, the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 90-day restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 90-day period, the restrictions imposed by this Agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event, provided, however, that in no event shall such restrictions extend past 124 days from the date of the Prospectus.

     (i) No Stabilization. The Company will not take, directly or indirectly, any action designed to or that could reasonably be expected to cause or result in any stabilization or manipulation of the price of the Shares.

     (j) Reports. So long as the Shares are outstanding, the Company will furnish to the Representatives, as soon as they are available, copies of all reports or other communications (financial or other) furnished to holders of the Shares, and copies of any reports and financial statements furnished to or filed with the Commission or any national securities exchange or automatic quotation system.

     (k) Record Retention. The Company will, pursuant to reasonable procedures developed in good faith, retain copies of each Issuer Free Writing Prospectus that is not filed with the Commission in accordance with Rule 433 under the Securities Act.

     6. Further Agreements of Selling Stockholders. Each Selling Stockholder covenants and agrees with each Underwriter and the Company that:

     (a) Clear Market. For a period of 90 days after the date of the Prospectus, such Selling Stockholder will not (i) offer, pledge, announce the intention to sell, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase or otherwise transfer or dispose of, directly or indirectly, any shares of Stock or any securities convertible into or exercisable or exchangeable for Stock or (ii) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Stock or such other securities, in cash or otherwise or (iii) make any demand for or exercise any right with respect to the registration of any shares of Stock or any security convertible into or exercisable or exchangeable for Stock without the prior written consent of the Representatives, in each case other than (1) the Shares to be sold by such Selling Stockholder hereunder, (2) transfers of shares of Stock or any security convertible into Stock as a bona fide gift or gifts, including to the Chase Foundation, (3) transfers of shares of Stock or other securities to directors, officers or employees of Chase Oil Corporation or its subsidiaries or affiliates and (4) distributions of shares of Stock or any security convertible into Stock to members or stockholders of such Selling Stockholder; provided that in the case of any transfer or distribution pursuant to clauses (2), (3) or (4) each donee, transferee or distributee shall execute and deliver to the Representatives a lock-up letter in the form of this paragraph and provided, further, that in the case of any transfer or distribution pursuant to clauses (2) or (4) no filing by any party (donor, donee, transferor or transferee) under Section 16(a) of the Securities Exchange Act of 1934, as amended, shall be required or shall be made voluntarily in connection with such transfer or distribution (other than a filing on a Form 5). Notwithstanding the foregoing, if (i) during the last 17 days of the 90-day restricted period, the Company issues an earnings release or material news or a material event relating to the Company occurs; or (ii) prior to the expiration of the 90-day restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 90-day period, the restrictions imposed by this Agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event; provided, however, that in no event shall such restrictions extend past 124 days from the date of the Prospectus.

     (b) Tax Form. It will deliver to the Representatives prior to or at the Closing Date a properly completed and executed United States Treasury Department Form W-9 (or other applicable form or statement specified by the Treasury Department regulations in lieu thereof) in order to facilitate the Underwriters’ documentation of their compliance with the reporting and withholding provisions of the Tax Equity and Fiscal Responsibility Act of 1982 with respect to the transactions herein contemplated.

     7. Certain Agreements of the Underwriters. Each Underwriter hereby represents and agrees that:

     (a) It has not and will not use, authorize use of, refer to, or participate in the planning for use of, any “free writing prospectus”, as defined in Rule 405 under the Securities Act (which term includes use of any written information furnished to the Commission by the Company and not incorporated by reference into the Registration Statement and any press release issued by the Company) other than (i) a free writing prospectus that contains no “issuer information” (as defined in Rule 433(h)(2) under the Securities

Act) that was not included (including through incorporation by reference) in the Preliminary Prospectus or a previously filed Issuer Free Writing Prospectus, (ii) any Issuer Free Writing Prospectus listed on Annex C or prepared pursuant to Section 3(c) or Section 5(c) above, or (iii) any free writing prospectus prepared by such underwriter and approved by the Company in advance in writing (each such free writing prospectus referred to in clauses (i) or (iii), an “Underwriter Free Writing Prospectus”).

     (b) It has not and will not distribute any Underwriter Free Writing Prospectus referred to in clause (a)(i) in a manner reasonably designed to lead to its broad unrestricted dissemination.

     (c) It has not and will not, without the prior written consent of the Company, use any free writing prospectus that contains the final terms of the Shares unless such terms have previously been included in a free writing prospectus filed with the Commission; provided that Underwriters may use a term sheet substantially in the form of Annex D hereto without the consent of the Company; provided further that any Underwriter using such term sheet shall notify the Company, and provide a copy of such term sheet to the Company, prior to, or substantially concurrently with, the first use of such term sheet.

     (d) It will, pursuant to reasonable procedures developed in good faith, retain copies of each free writing prospectus used or referred to by it, in accordance with Rule 433 under the Securities Act.

     (e) It is not subject to any pending proceeding under Section 8A of the Securities Act with respect to the offering (and will promptly notify the Company and the Selling Stockholders if any such proceeding against it is initiated during the Prospectus Delivery Period).

     8. Conditions of Underwriters’ Obligations. The obligation of each Underwriter to purchase the Underwritten Shares on the Closing Date or the Option Shares on the Additional Closing Date, as the case may be, as provided herein is subject to the performance by the Company and the Selling Stockholders of their respective covenants and other obligations hereunder and to the following additional conditions:

     (a) Registration Compliance; No Stop Order. No order suspending the effectiveness of the Registration Statement shall be in effect, and no proceeding for such purpose or pursuant to Section 8A under the Securities Act shall be pending before or threatened by the Commission; the Prospectus and each Issuer Free Writing Prospectus shall have been timely filed with the Commission under the Securities Act (in the case of an Issuer Free Writing Prospectus, to the extent required by Rule 433 under the Securities Act) and in accordance with Section 5(a) hereof; and all requests by the Commission for additional information shall have been complied with to the reasonable satisfaction of the Representatives.

     (b) Representations and Warranties. The representations and warranties of the Company and the Selling Stockholders contained herein shall be true and correct on the date hereof and on and as of the Closing Date or the Additional Closing Date, as the case may be; and the statements of the Company and its officers and of each of the Selling Stockholders made in any certificates delivered pursuant to this Agreement shall be true and correct on and as of the Closing Date or the Additional Closing Date, as the case may be.

     (c) No Downgrade. Subsequent to the execution and delivery of this Agreement, (i) no downgrading shall have occurred in the rating accorded any securities or preferred stock of or guaranteed by the Company or any of its subsidiaries by any “nationally recognized statistical rating organization”, as such term is defined by the Commission for purposes of Rule 436(g)(2) under the Securities Act and (ii) no such organization shall have publicly announced that it has under surveillance or review, or has changed its outlook with respect to, its rating of any securities or preferred stock of or guaranteed by the

Company or any of its subsidiaries (other than an announcement with positive implications of a possible upgrading).

     (d) No Material Adverse Change. No event or condition of a type described in Section 3(f) hereof shall have occurred or shall exist, which event or condition is not described in the Time of Sale Information (excluding any amendment or supplement thereto) and the Prospectus (excluding any amendment or supplement thereto) and the effect of which in the judgment of the Representatives makes it impracticable or inadvisable to proceed with the offering, sale or delivery of the Shares on the Closing Date or the Additional Closing Date, as the case may be, on the terms and in the manner contemplated by this Agreement, the Time of Sale Information and the Prospectus.

     (e) Officer’s Certificate. The Representatives shall have received on and as of the Closing Date or the Additional Closing Date, as the case may be, a certificate of each of (i) the chief financial officer or chief accounting officer of the Company and one additional senior executive officer of the Company who is satisfactory to the Representatives (A) confirming that such officers have carefully reviewed the Registration Statement, the Time of Sale Information and the Prospectus and, to the knowledge of such officers, the representations set forth in Sections 3(b) and 3(d) hereof are true and correct, (B) confirming that the other representations and warranties of the Company in this Agreement are true and correct and that the Company has complied with all agreements and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to such Closing Date and (C) to the effect set forth in paragraphs (a), (c) and (d) above and (ii) the Selling Stockholders, in form and substance reasonably satisfactory to the Representatives, (A) confirming that the representations of such Selling Stockholder set forth in Sections 4(e), 4(f) and 4(g) hereof are true and correct and (B) confirming that the other representations and warranties of such Selling Stockholder in this Agreement are true and correct and that such Selling Stockholder has complied with all agreements and satisfied all conditions on their part to be performed or satisfied hereunder at or prior to such Closing Date.

     (f) Comfort Letters. On the date of this Agreement and on the Closing Date or the Additional Closing Date, as the case may be, Grant Thornton LLP shall have furnished to the Representatives, at the request of the Company, letters, dated the respective dates of delivery thereof and addressed to the Underwriters, in form and substance reasonably satisfactory to the Representatives, containing statements and information of the type customarily included in accountants’ “comfort letters” to underwriters with respect to the financial statements and certain financial information contained in the Registration Statement, the Time of Sale Information and the Prospectus; provided, that the letter delivered on the Closing Date or the Additional Closing Date, as the case may be, shall use a “cut-off” date no more than three business days prior to such Closing Date or such Additional Closing Date, as the case may be.

     (g) Reserve Letters. On the date of this Agreement and on the Closing Date or the Additional Closing Date, as the case may be, each of Netherland, Sewell & Associates, Inc. and Cawley, Gillespie & Associates, Inc. shall have furnished to the Representatives, at the request of the Company, reserve report confirmation letters, dated the respective dates of delivery thereof and addressed to the Underwriters, in form and substance reasonably satisfactory to the Representatives, containing statements and information of the type customarily included in such letters to underwriters with respect to the reserve and other operational information contained in the Registration Statement, the Time of Sale Information and the Prospectus.

     (h) Opinion of Counsel for the Company. Each of (i) Vinson & Elkins L.L.P., counsel for the Company, and (ii) David W. Copeland, General Counsel of the Company, shall have furnished to the Representatives, at the request of the Company, their respective written opinions, dated the Closing Date or the Additional Closing Date, as the case may be, and addressed to the Underwriters, in form and

substance reasonably satisfactory to the Representatives, to the effect set forth in Annex A-1 and A-2 hereto, respectively.

     (i) Opinions of Counsel for Selling Stockholders. Each of (i) Vinson & Elkins L.L.P., counsel for the Company, (ii) Bracewell & Giuliani, LLP, counsel for the Chase Oil Corporation and Caza Energy LLC and (iii) Hinkle, Hensley, Shanor & Martin, LLP, local counsel for the Chase Oil Corporation and Caza Energy LLC, shall have furnished the Representatives, at the request of the Selling Stockholders, their written opinions, dated the Closing Date and addressed to the Underwriters, in form and substance reasonably satisfactory to the Representatives, to the effect set forth in Annex B-1, Annex B-2 and Annex B-3 hereto.

     (j) Opinion of Counsel for the Underwriters. The Representatives shall have received on and as of the Closing Date or the Additional Closing Date, as the case may be, a written opinion of Cahill Gordon & Reindel llp, counsel for the Underwriters, with respect to such matters as the Representatives may reasonably request, and such counsel shall have received such documents and information as they may reasonably request to enable them to pass upon such matters.

     (k) No Legal Impediment to Issuance. No action shall have been taken and no statute, rule, regulation or order shall have been enacted, adopted or issued by any federal, state or foreign governmental or regulatory authority that would, as of the Closing Date or the Additional Closing Date, as the case may be, prevent the issuance or sale of the Shares; and no injunction or order of any federal, state or foreign court shall have been issued that would, as of the Closing Date or the Additional Closing Date, as the case may be, prevent the issuance or sale of the Shares.

     (l) Good Standing. The Representatives shall have received on and as of the Closing Date or the Additional Closing Date, as the case may be, satisfactory evidence of the good standing of the Company and its subsidiaries in their respective jurisdictions of organization and their good standing as foreign entities in such other jurisdictions as the Representatives may reasonably request, in each case in writing or any standard form of telecommunication from the appropriate Governmental Authorities of such jurisdictions.

     (m) Exchange Listing. The Shares to be delivered on the Closing Date or Additional Closing Date, as the case may be, shall be listed on the New York Stock Exchange.

     (n) Lock-up Agreements. The “lock-up” agreements, each substantially in the form of Exhibit A hereto, between you and certain shareholders, the Selling Stockholders, officers and directors of the Company relating to sales and certain other dispositions of shares of Stock or certain other securities, delivered to you on or before the date hereof, shall be in full force and effect on the Closing Date or the Additional Closing Date, as the case may be.

     (o) Additional Documents. On or prior to the Closing Date or the Additional Closing Date, as the case may be, the Company and the Selling Stockholders shall have furnished to the Representatives such further certificates and documents as the Representatives may reasonably request.

     All opinions, letters, certificates and evidence mentioned above or elsewhere in this Agreement shall be deemed to be in compliance with the provisions hereof only if they are in form and substance reasonably satisfactory to counsel for the Underwriters.

     9. Indemnification and Contribution.

     (a) Indemnification of the Underwriters by Company. The Company agrees to indemnify and hold harmless each Underwriter, its affiliates, directors and officers and each person, if any, who controls such Underwriter within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act, from and against any and all losses, claims, damages and liabilities (including, without limitation, legal fees and other expenses incurred in connection with any suit, action or proceeding or any claim asserted, as such fees and expenses are incurred), joint or several, that arise out of, or are based upon, (i) any untrue statement or alleged untrue statement of a material fact contained in the Registration Statement or caused by any omission or alleged omission to state therein a material fact required to be stated therein or necessary in order to make the statements therein, not misleading, (ii) or any untrue statement or alleged untrue statement of a material fact contained in the Prospectus (or any amendment or supplement thereto), any Issuer Free Writing Prospectus or any Time of Sale Information (including any Time of Sale Information that has subsequently been amended), or caused by any omission or alleged omission to state therein a material fact necessary in order to make the statements therein, in light of the circumstances under which they were made, not misleading, in each case except insofar as such losses, claims, damages or liabilities arise out of, or are based upon, any untrue statement or omission or alleged untrue statement or omission made in reliance upon and in conformity with any information relating to any Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in subsection (c) below.

     (b) Indemnification of Underwriters by Selling Stockholders. (i) Each of the Non-Chase Stockholders agrees to indemnify and hold harmless each Underwriter, its affiliates, directors and officers and each person, if any, who controls such Underwriter within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act to the same extent as the indemnity set forth in paragraph (a) above for any and all Non-Chase Stockholder Information relating to such Non-Chase Stockholder.

     (ii) (A) Each of the Chase Stockholders agrees to indemnify and hold harmless each Underwriter, its affiliates, directors and officers and each person, if any, who controls such Underwriter within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act to the same extent as the indemnity set forth in paragraph (a) above for any and all Chase Information relating to such Chase Stockholder; and (B) the Chase Stockholders also agree, jointly and severally, to indemnify and hold harmless each Underwriter, its affiliates, directors and officers and each person, if any, who controls such Underwriter within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act to the same extent as the indemnity set forth in paragraph (a) above for any and all Chase Information, provided, however, that the indemnity of each Chase Stockholder under this clause (B) shall be limited to 50% of the net proceeds (after deducting underwriting discounts but before deducting any other expenses) received by such Chase Stockholder pursuant to its sale of Shares to the Underwriters pursuant to this Agreement.

     (c) Indemnification of the Company and the Selling Stockholders. Each Underwriter agrees, severally and not jointly, to indemnify and hold harmless the Company, each Selling Stockholder, their directors, their officers who signed the Registration Statement and each person, if any, who controls the Company within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act to the same extent as the indemnity set forth in paragraph (a) above, but only with respect to any losses, claims, damages or liabilities that arise out of, or are based upon, any untrue statement or omission or alleged untrue statement or omission made in reliance upon and in conformity with any information relating to such Underwriter furnished to the Company in writing by such Underwriter through the Representatives expressly for use in the Registration Statement, the Prospectus (or any amendment or supplement thereto), any Issuer Free Writing Prospectus or any Time of Sale Information, it being understood and agreed upon that the only such information furnished by any Underwriter consists of the following information in the

Prospectus furnished on behalf of each Underwriter: the concession and reallowance figures appearing in the fourth paragraph under the caption “Underwriting” and the information concerning stabilizing transactions and other information appearing under the caption “Underwriting” in the two paragraphs beginning with the words “The underwriters have advised us that they may make short sales...” and “The underwriters have advised us that, pursuant to Regulation M...”

     (c) Notice and Procedures. If any suit, action, proceeding (including any governmental or regulatory investigation), claim or demand shall be brought or asserted against any person in respect of which indemnification may be sought pursuant to either paragraph (a), (b), or (c) above, such person (the “Indemnified Person”) shall promptly notify the person against whom such indemnification may be sought (the “Indemnifying Person”) in writing; provided that the failure to notify the Indemnifying Person shall not relieve it from any liability that it may have under this Section 9 except to the extent that it has been materially prejudiced (through the forfeiture of substantive rights or defenses) by such failure; and provided further, that the failure to notify the Indemnifying Person shall not relieve it from any liability that it may have to an Indemnified Person otherwise than under this Section 9. If any such proceeding shall be brought or asserted against an Indemnified Person and it shall have notified the Indemnifying Person thereof, the Indemnifying Person shall retain counsel reasonably satisfactory to the Indemnified Person (who shall not, without the consent of the Indemnified Person, be counsel to the Indemnifying Person) to represent the Indemnified Person in such proceeding and shall pay the fees and expenses of such counsel related to such proceeding, as incurred. In any such proceeding, any Indemnified Person shall have the right to retain its own counsel, but the fees and expenses of such counsel shall be at the expense of such Indemnified Person unless (i) the Indemnifying Person and the Indemnified Person shall have mutually agreed to the contrary or (ii) the Indemnifying Person has failed within a reasonable time to retain counsel reasonably satisfactory to the Indemnified Person. It is understood and agreed that the Indemnifying Person shall not, in connection with any proceeding or related proceeding in the same jurisdiction, be liable for the fees and expenses of more than one separate firm (in addition to any local counsel) for all Indemnified Persons, and that all such fees and expenses shall be paid or reimbursed as they are incurred. The Indemnifying Person shall not be liable for any settlement of any proceeding effected without its written consent, but if settled with such consent or if there be a final judgment for the plaintiff, the Indemnifying Person agrees to indemnify each Indemnified Person from and against any loss or liability by reason of such settlement or judgment. Notwithstanding the foregoing sentence, if at any time an Indemnified Person shall have requested that an Indemnifying Person reimburse the Indemnified Person for fees and expenses of counsel as contemplated by this paragraph, the Indemnifying Person shall be liable for any settlement of any proceeding effected without its written consent if (i) such settlement is entered into more than 30 days after receipt by the Indemnifying Person of such request and (ii) the Indemnifying Person shall not have reimbursed the Indemnified Person in accordance with such request prior to the date of such settlement. No Indemnifying Person shall, without the written consent of the Indemnified Person, effect any settlement of any pending or threatened proceeding in respect of which any Indemnified Person is or could have been a party and indemnification could have been sought hereunder by such Indemnified Person, unless such settlement (x) includes an unconditional release of such Indemnified Person, in form and substance reasonably satisfactory to such Indemnified Person, from all liability on claims that are the subject matter of such proceeding and (y) does not include any statement as to or any admission of fault, culpability or a failure to act by or on behalf of any Indemnified Person.

     (d) Contribution. If the indemnification provided for in paragraphs (a), (b), and (c) above is unavailable to an Indemnified Person or insufficient in respect of any losses, claims, damages or liabilities referred to therein, then each Indemnifying Person under such paragraph, in lieu of indemnifying such Indemnified Person thereunder, shall contribute to the amount paid or payable by such Indemnified Person as a result of such losses, claims, damages or liabilities (i) in such proportion as is appropriate to reflect the relative benefits received by the Company and the Selling Stockholders, on the one hand, and the

Underwriters, on the other, from the offering of the Shares or (ii) if the allocation provided by clause (i) is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) but also the relative fault of the Company and the Selling Stockholders, on the one hand, and the Underwriters, on the other, in connection with the statements or omissions that resulted in such losses, claims, damages or liabilities, as well as any other relevant equitable considerations. The relative benefits received by the Company and the Selling Stockholders, on the one hand, and the Underwriters, on the other, shall be deemed to be in the same respective proportions as the net proceeds (before deducting expenses) received by the Company and the Selling Stockholders from the sale of the Shares and the total underwriting discounts and commissions received by the Underwriters in connection therewith, in each case as set forth in the table on the cover of the Prospectus, bear to the aggregate offering price of the Shares. The relative fault of the Company and the Selling Stockholders, on the one hand, and the Underwriters, on the other, shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company and the Selling Stockholders or by the Underwriters, and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission.

     (e) Limitation on Liability. The Company, the Selling Stockholders and the Underwriters agree that it would not be just and equitable if contribution pursuant to this Section 9 were determined by pro rata allocation (even if the Selling Stockholders or the Underwriters were treated as one entity for such purpose) or by any other method of allocation that does not take account of the equitable considerations referred to in paragraph (e) above. The amount paid or payable by an Indemnified Person as a result of the losses, claims, damages and liabilities referred to in paragraph (e) above shall be deemed to include, subject to the limitations set forth above, any legal or other expenses incurred by such Indemnified Person in connection with any such action or claim. Notwithstanding the provisions of this Section 9, in no event shall an Underwriter be required to contribute any amount in excess of the amount by which the total underwriting discounts and commissions received by such Underwriter with respect to the offering of the Shares exceeds the amount of any damages that such Underwriter has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The Underwriters’ obligations to contribute pursuant to this Section 9 are several in proportion to their respective purchase obligations hereunder and not joint. The liability of each Selling Stockholder under such Selling Stockholder’s representations, warranties and covenants and agreements contained in Section 4 hereof and Section 6 hereof and under the indemnity and contribution provisions of this Section 9 shall be limited to an amount equal to the net proceeds received by such Selling Stockholder for the sale of Shares by such Selling Stockholder to the Underwriters pursuant to this Agreement, provided, however, that the liability of the Chase Stockholders, other than pursuant to Section 9(b)(ii)(A), with respect to Section 9(b)(ii), is limited as specified in Section 9(b)(ii)(B).

     (f) Non-Exclusive Remedies. The remedies provided for in this Section 9 are not exclusive and shall not limit any rights or remedies which may otherwise be available to any Indemnified Person at law or in equity.

     10. Effectiveness of Agreement. This Agreement shall become effective upon the execution and delivery hereof by the parties hereto.

     11. Termination. This Agreement may be terminated in the absolute discretion of the Representatives, by notice to the Company and the Selling Stockholders, if after the execution and delivery of this Agreement and prior to the Closing Date or, in the case of the Option Shares, prior to the Additional

Closing Date (i) trading generally shall have been suspended or materially limited on or by any of the New York Stock Exchange, the National Association of Securities Dealers, Inc., the Chicago Board Options Exchange, the Chicago Mercantile Exchange or the Chicago Board of Trade; (ii) trading of any securities issued or guaranteed by the Company shall have been suspended on any exchange or in any over-the-counter market; (iii) a general moratorium on commercial banking activities shall have been declared by federal or New York State authorities; or (iv) there shall have occurred any outbreak or escalation of hostilities or any change in financial markets or any calamity or crisis, either within or outside the United States, that, in the judgment of the Representatives, is material and adverse and makes it impracticable or inadvisable to proceed with the offering, sale or delivery of the Shares on the Closing Date or the Additional Closing Date, as the case may be, on the terms and in the manner contemplated by this Agreement, the Time of Sale Information and the Prospectus.

     12. Defaulting Underwriter.

     (a) If, on the Closing Date or the Additional Closing Date, as the case may be, any Underwriter defaults on its obligation to purchase the Shares that it has agreed to purchase hereunder on such date, the non-defaulting Underwriters may in their discretion arrange for the purchase of such Shares by other persons satisfactory to the Company and the Selling Stockholders on the terms contained in this Agreement. If, within 36 hours after any such default by any Underwriter, the non-defaulting Underwriters do not arrange for the purchase of such Shares, then the Company and the Selling Stockholders shall be entitled to a further period of 36 hours within which to procure other persons satisfactory to the non-defaulting Underwriters to purchase such Shares on such terms. If other persons become obligated or agree to purchase the Shares of a defaulting Underwriter, either the non-defaulting Underwriters or the Company and the Selling Stockholders may postpone the Closing Date or the Additional Closing Date, as the case may be, for up to five full business days in order to effect any changes that in the opinion of counsel for the Company, counsel for the Selling Stockholders or counsel for the Underwriters may be necessary in the Registration Statement and the Prospectus or in any other document or arrangement, and the Company agrees to promptly prepare any amendment or supplement to the Registration Statement and the Prospectus that effects any such changes. As used in this Agreement, the term “Underwriter” includes, for all purposes of this Agreement unless the context otherwise requires, any person not listed in Schedule 1 hereto that, pursuant to this Section 12, purchases Shares that a defaulting Underwriter agreed but failed to purchase.

     (b) If, after giving effect to any arrangements for the purchase of the Shares of a defaulting Underwriter or Underwriters by the non-defaulting Underwriters and the Company and the Selling Stockholders as provided in paragraph (a) above, the aggregate number of Shares that remain unpurchased on the Closing Date or the Additional Closing Date, as the case may be does not exceed one-eleventh of the aggregate number of Shares to be purchased on such date, then the Company and the Selling Stockholders shall have the right to require each non-defaulting Underwriter to purchase the number of Shares that such Underwriter agreed to purchase hereunder on such date plus such Underwriter’s pro rata share (based on the number of Shares that such Underwriter agreed to purchase on such date) of the Shares of such defaulting Underwriter or Underwriters for which such arrangements have not been made.

     (c) If, after giving effect to any arrangements for the purchase of the Shares of a defaulting Underwriter or Underwriters by the non-defaulting Underwriters and the Company and the Selling Stockholders as provided in paragraph (a) above, the aggregate number of Shares that remain unpurchased on the Closing Date or the Additional Closing Date, as the case may be, exceeds one-eleventh of the aggregate amount of Shares to be purchased on such date, or if the Company and the Selling Stockholders shall not exercise the right described in paragraph (b) above, then this Agreement or, with respect to any Additional Closing Date, the obligation of the Underwriters to purchase Shares on the Additional Closing

Date, as the case may be, shall terminate without liability on the part of the non-defaulting Underwriters. Any termination of this Agreement pursuant to this Section 12 shall be without liability on the part of the Company and the Selling Stockholders, except that the Company will continue to be liable for the payment of expenses as set forth in Section 13 hereof and except that the provisions of Section 9 hereof shall not terminate and shall remain in effect.

     (d) Nothing contained herein shall relieve a defaulting Underwriter of any liability it may have to the Company, the Selling Stockholders or any non-defaulting Underwriter for damages caused by its default.

     13. Payment of Expenses. (a) Whether or not the transactions contemplated by this Agreement are consummated or this Agreement is terminated, the Company will pay or cause to be paid all costs and expenses incident to the performance of its obligations hereunder, including without limitation, (i) the costs incident to the sale, preparation and delivery of the Shares and any taxes payable in that connection; (ii) the costs incident to the preparation, printing and filing under the Securities Act of the Registration Statement, the Preliminary Prospectus, any Issuer Free Writing Prospectus, any Time of Sale Information and the Prospectus (including all exhibits, amendments and supplements thereto) and the distribution thereof; (iii) the costs of reproducing and distributing this Agreement; (iv) the fees and expenses of the Company’s counsel and independent accountants; (v) the fees and expenses incurred in connection with the registration or qualification and determination of eligibility for investment of the Shares under the laws of such jurisdictions as the Representatives may designate (including the related reasonable fees and expenses of counsel for the Underwriters); (vi) the cost of preparing stock certificates; (vii) the costs and charges of any transfer agent and any registrar; (viii) all expenses and application fees incurred in connection with any filing with, and clearance of the offering by, the Financial Industry Regulatory Authority, Inc and (ix) all expenses incurred by the Company in connection with any “road show” presentation to potential investors; provided that notwithstanding clause (ix) above, the Underwriters shall pay one-half of the lease expenses associated with any airplane which is used for the purposes of such “road show” presentations.

     (b) If (i) the Selling Stockholders for any reason fail to tender the Shares for delivery to the Underwriters or (ii) the Underwriters decline to purchase the Shares for any reason permitted under this Agreement (other than Section 11), the Company agrees to reimburse the Underwriters for all out-of-pocket costs and expenses (including the fees and expenses of their counsel) reasonably incurred by the Underwriters in connection with this Agreement and the offering contemplated hereby.

     14. Persons Entitled to Benefit of Agreement. This Agreement shall inure to the benefit of and be binding upon the parties hereto and their respective successors and the officers and directors and any controlling persons referred to in Section 9 hereof. Nothing in this Agreement is intended or shall be construed to give any other person any legal or equitable right, remedy or claim under or in respect of this Agreement or any provision contained herein. No purchaser of Shares from any Underwriter shall be deemed to be a successor merely by reason of such purchase.

     15. Survival. The respective indemnities, rights of contribution, representations, warranties and agreements of the Company, the Selling Stockholders and the Underwriters contained in this Agreement or made by or on behalf of the Company, the Selling Stockholders or the Underwriters pursuant to this Agreement or any certificate delivered pursuant hereto shall survive the delivery of and payment for the Shares and shall remain in full force and effect, regardless of any termination of this Agreement or any investigation made by or on behalf of the Company, the Selling Stockholders or the Underwriters.

     16. Certain Defined Terms. For purposes of this Agreement, (a) except where otherwise expressly provided, the term “affiliate” has the meaning set forth in Rule 405 under the Securities Act;

(b) the term “business day” means any day other than a day on which banks are permitted or required to be closed in New York City; and (c) the term “subsidiary” has the meaning set forth in Rule 405 under the Securities Act .

     17. Miscellaneous.

     (a) Authority of the Representatives. Any action by the Underwriters hereunder may be taken by the Representatives on behalf of the Underwriters, and any such action taken by Representatives shall be binding upon the Underwriters.

     (b) Notices. All notices and other communications hereunder shall be in writing and shall be deemed to have been duly given if mailed or transmitted and confirmed by any standard form of telecommunication. Notices to the Underwriters shall be given to the Representatives c/o J.P. Morgan Securities Inc., 277 Park Avenue, New York, New York 10172 (fax: (212)  ###-###-####); Attention: Equity Syndicate Desk, with a copy to Gerald S. Tanenbaum, Cahill Gordon & Reindel LLP, 80 Pine Street, New York, New York 10005 (fax: (212)  ###-###-####). Notices to the Company shall be given to it at Concho Resources Inc., 550 W. Texas Avenue, Suite 1300, Midland, Texas 79701, (fax: (432) 683-7441); Attention: David W. Copeland, Vice President and General Counsel, with a copy to T. Mark Kelly, Vinson & Elkins L.L.P., 1001 Fannin, Suite 2500, Houston, Texas 77002 (fax: (713)  ###-###-####). Notice to the Chase Stockholders shall be given to the Chase Attorney-in-Fact to Robert Chase, Brad Bartek and Johnny Knorr, c/o Mack Energy Corporation, P.O. Box 960, Artesia, NM 88211-0960, with a copy to William S. Anderson, Bracewell & Guiliani LLP, 711 Louisiana Street, Suite 2300, Houston, Texas 77002 (fax: (713)  ###-###-####). Notice to the Non-Chase Stockholders shall be given to the Non-Chase Attorney-in-Fact David W. Copeland, 550 W. Texas Avenue, Suite 1300, Midland, Texas 79701, (fax: (432)  ###-###-####).

     (c) Governing Law. This Agreement shall be governed by and construed in accordance with the laws of the State of New York.

     (d) Counterparts. This Agreement may be signed in counterparts (which may include counterparts delivered by any standard form of telecommunication), each of which shall be an original and all of which together shall constitute one and the same instrument.

     (e) Amendments or Waivers. No amendment or waiver of any provision of this Agreement, nor any consent or approval to any departure therefrom, shall in any event be effective unless the same shall be in writing and signed by the parties hereto.

     (f) Headings. The headings herein are included for convenience of reference only and are not intended to be part of, or to affect the meaning or interpretation of, this Agreement.

     If the foregoing is in accordance with your understanding, please indicate your acceptance of this Agreement by signing in the space provided below.

S-1

S-2

S-1

Accepted: December [ ], 2007

J.P. MORGAN SECURITIES INC.
BANC OF AMERICA SECURITIES LLC

For themselves and on behalf of the
several Underwriters listed
in Schedule 1 hereto.

S-1

Schedule 1

				Number of			Number of
	Underwriter			Underwritten Shares			Option Shares
	J.P. Morgan Securities Inc.
	Banc of America Securities LLC
	Total			[                    ]			[                    ]

Schedule 2

				Number of Underwritten Shares:
	Chase Oil Corporation
	Caza Energy LLC
	Richard L. Chase
	Robert C. Chase
	Gerene Dianne Chase Ferguson
	[Other Selling Stockholders]

Schedule 3

	Each Option Selling Stockholder			Number of Option Shares
	Chase Oil Corporation
	Caza Energy LLC
	Richard L. Chase
	Robert C. Chase
	Gerene Dianne Chase Ferguson
	[Other Selling Stockholders]

Schedule 4

	Chase Stockholders			Attorney-in-Fact
	Chase Oil Corporation			Robert Chase, Brad Bartek and Johnny Knorr
	Caza Energy LLC			Robert Chase, Brad Bartek and Johnny Knorr

Schedule 5

	Each Non-Chase Stockholder			Attorney-in-Fact
	Richard L. Chase			Robert Chase, Brad Bartek and Johnny Knorr
	Robert C. Chase			Robert Chase, Brad Bartek and Johnny Knorr
	Gerene Dianne Chase Ferguson			Robert Chase, Brad Bartek and Johnny Knorr
	[Other Selling Stockholders]

Annex A-1

[Form of Opinion of Counsel for the Company]

     (-) The Registration Statement was declared effective under the Securities Act as of the date and time specified in such opinion; the Prospectus was filed with the Commission pursuant to the subparagraph of Rule 424(b) under the Securities Act specified in such opinion on the date specified therein; and, to such counsel’s knowledge, no order suspending the effectiveness of the Registration Statement has been issued and no proceeding for that purpose or pursuant to Section 8A of the Securities Act against the Company or in connection with the offering is pending or threatened by the Commission.

     (-) The Registration Statement, the Marketing Preliminary Prospectus, each Issuer Free Writing Prospectus included in the Time of Sale Information and the Prospectus (other than the financial statements and notes and related schedules and other financial and accounting data and the oil and natural gas reserve estimates included therein or omitted therefrom as to which such counsel need express no opinion) appear on their face to comply as to form in all material respects with the requirements of the Securities Act.

     (-) The Company has the requisite corporate power and authority to execute and deliver the Underwriting Agreement and to perform its obligations thereunder.

     (-) The Underwriting Agreement has been duly authorized, executed and delivered by the Company.

     (-) The execution, delivery and performance by the Company of the Underwriting Agreement, and compliance by the Company with the terms of, and the consummation of the transactions contemplated by, the Underwriting Agreement will not (i) conflict with or result in a breach or violation of any of the terms or provisions of, or constitute a default under, or result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of the Company or any of its subsidiaries pursuant to, any document filed as an exhibit to the Registration Statement, (ii) result in any violation of the provisions of the charter or by-laws or similar organizational documents of the Company or any of its subsidiaries or (iii) result in the violation of any law or statute or any judgment, order or regulation of any court or arbitrator or governmental or regulatory authority known to such counsel except, in the case of clauses (i) and (iii) above, for such conflict, breach or violation that would not, individually or in the aggregate, have a Material Adverse Effect. With respect to clause (iii) above, we express no opinion as to the application of any state securities or Blue Sky laws or federal or state antifraud laws, rules or regulations.

     (-) No consent, approval, authorization, order, registration or qualification of or with any court or arbitrator or governmental or regulatory authority is required for the execution, delivery and performance by the Company of the Underwriting Agreement and compliance by the Company with the terms thereof and the consummation of the transactions contemplated by the Underwriting Agreement, except for the registration of the Shares under the Securities Act and such consents, approvals, authorizations, orders and registrations or qualifications as may be required under applicable state securities laws in connection with the purchase and distribution of the Shares by the Underwriters, and any consent, approval, authorization, order, registration or qualification that either has been, or prior to the Closing Date will have been, obtained or made, or which if not obtained or made, would not, individually or in the aggregate, have a Material Adverse Effect.

     (-) The descriptions in the Registration Statement, the Time of Sale Information and the Prospectus under the headings “Material U.S. federal tax consequences for non-U.S. holders of our common

stock,” “Description of capital stock”, “Business — Applicable laws and regulations” (other than the description under the heading “Grayburg— Jackson West Cooperative Unit Regulatory Matter”) and “Underwriting”, and in the Registration Statement in item 14, to the extent that they constitute summaries of the terms of stock, matters of law or regulation or legal conclusions, are accurate in all material respects.

     (-) The Company is not and, after giving effect to the offering and sale of the Shares as described in the Registration Statement, the Time of Sale Information and the Prospectus, will not be required to register as an “investment company” within the meaning of the Investment Company Act.

     Such counsel shall also state that they have participated in conferences with representatives of the Company and with representatives of its independent accountants and counsel at which conferences the contents of the Registration Statement, the Time of Sale Information and the Prospectus and any amendment and supplement thereto and related matters were discussed and, although such counsel assume no responsibility for, or express any opinion regarding (other than as listed in opinion [ ] above), the accuracy, completeness or fairness of the Registration Statement, the Time of Sale Information, the Prospectus and any amendment or supplement thereto (except as expressly provided above), based upon the participation described above (relying as to factual matters in respect to the determination by us of materiality to the extent we deem reasonable upon statements of fact made to us by representatives of the Company) and subject to the next succeeding sentence, nothing has come to the attention of such counsel to cause such counsel to believe that the Registration Statement, at the time of its effective date (including the information, if any, deemed pursuant to Rule 430A, 430B or 430C to be part of the Registration Statement at the time of effectiveness), contained any untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary to make the statements therein not misleading, that the Time of Sale Information, at the Time of Sale (which such counsel may assume to be the date of the Underwriting Agreement) contained any untrue statement of a material fact or omitted to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading or that the Prospectus or any amendment or supplement thereto as of its date and the Closing Date contains any untrue statement of a material fact or omits to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading . In making the foregoing statement, such counsel will not express any comment or belief with respect to the financial statements and notes and related schedules (and other financial and accounting data derived therefrom), and the oil and natural gas reserve estimates included in or omitted from the Registration Statement, the Time of Sale Information or the Prospectus.

     In rendering such opinion, such counsel may rely as to matters of fact on certificates of responsible officers of the Company and public officials that are furnished to the Underwriters.

     The opinion of Vinson & Elkins L.L.P. described above shall be rendered to the Underwriters at the request of the Company and shall so state therein.

Annex A-2

[Form of Opinion of General Counsel of the Company]

     (-) The Company and each of its subsidiaries have been duly organized and are validly existing and in good standing under the laws of their respective jurisdictions of organization, are duly qualified to do business and are in good standing in each jurisdiction in which their respective ownership or lease of property or the conduct of their respective businesses requires such qualification, and have all power and authority necessary to own or hold their respective properties and to conduct the businesses in which they are engaged, except where the failure to be in good standing or so qualified or have such power or authority would not, individually or in the aggregate, have a Material Adverse Effect.

     (-) The Company has authorized capital stock as set forth in the Registration Statement, the Time of Sale Information and the Prospectus under the heading “Description of capital stock”; all of the outstanding shares of capital stock of the Company have been duly and validly authorized and issued and are fully paid and non-assessable; the capital stock of the Company conforms in all material respects to the description thereof contained in the Registration Statement, the Time of Sale Information and the Prospectus.

     (-) To the knowledge of such counsel, except as described in the Registration Statement, the Time of Sale Information and the Prospectus, there are no legal, governmental or regulatory investigations, actions, suits or proceedings pending to which the Company or any of its subsidiaries is or is reasonably expected to be a party or to which any property of the Company or any of its subsidiaries is or is reasonably expected to be the subject which, individually or in the aggregate, if determined adversely to the Company or any of its subsidiaries, could reasonably be expected to have a Material Adverse Effect; and to the knowledge of such counsel, no such investigations, actions, suits or proceedings are threatened or contemplated by any governmental or regulatory authority or threatened by others.

Annex B-1

[Form of Opinion of Counsel For
The Non-Chase Selling Stockholders]

     (   ) The Underwriting Agreement has been duly authorized, executed and delivered by or on behalf of each of the Selling Stockholders.

     (   ) A Power of Attorney and a Custody Agreement have been duly authorized, executed and delivered by each Selling Stockholder and constitute valid and binding agreements of each Selling Stockholder in accordance with their terms.

     (   ) Upon payment for the Selling Stockholder Shares to be sold by the Selling Stockholder to the Underwriters as provided in the Underwriting Agreement, the delivery of the certificates representing such Selling Stockholder Shares to Cede & Co. (“Cede”) or such other nominee as may be designated by The Depository Trust Company (“DTC”), the registration of such Selling Stockholder Shares in the name of Cede or such other nominee and the crediting of such Selling Stockholder Shares by book entry on the records of DTC (acting in its capacity as a securities intermediary, as such term is defined in Section 8-102 of the Uniform Commercial Code as in effect in the State of New York (the “NYUCC”)) to security accounts ( as such term defined in Section 8-501 of the Uniform Commercial Code (the “UCC”)) in the name of the Underwriters (assuming that neither DTC nor any of the Underwriters has notice of any adverse claim (as such phrase is defined in Section 8-102 of the UCC) to such Selling Stockholder Shares or any security entitlement in respect thereof), (i) DTC shall be a “protected purchaser” of such Selling Stockholder Shares within the meaning of Section 8-303 of the UCC, (ii) under Section 8-501 of the UCC, the Underwriters will acquire a security entitlement in respect of such Selling Stockholder Shares and (iii) to the extent governed by Article 8 of the UCC, no action based on any “adverse claim” (as defined in Section 8-102 of the UCC) to such Selling Stockholder Shares may be asserted against the Underwriters; it being understood that for purposes of this opinion, such counsel may assume that when such payment, delivery and crediting occur, (A) such Selling Stockholder Shares will have been registered in the name of Cede or such other nominee as may be designated by DTC, in each case on the Company’s share registry in accordance with its certificate of incorporation, bylaws and applicable law, (B) DTC will be registered as a “clearing corporation” within the meaning of Section 8-102 of the UCC and (C) appropriate entries to the securities account or accounts in the names of the Underwriters on the records of DTC will have been made pursuant to the UCC.

     The opinion of counsel described above shall be rendered to the Underwriters at the request of the Selling Stockholders and shall so state therein.

Annex B-2

[Form of Opinion of Counsel For
The Chase Selling Stockholders]

     (   ) The Underwriting Agreement has been duly executed and delivered by or on behalf of each of the Selling Stockholders.

     (   ) A Power of Attorney and Custody Agreement has been duly executed and delivered by each of the Selling Stockholders and, assuming the due authorization, execution and delivery thereof by each of the attorneys-in-fact named therein and the Custodian, constitutes a valid and binding agreement of each such Selling Stockholder enforceable against each such Selling Stockholder in accordance with its terms.

     (   ) Upon payment by each Underwriter for the Secondary Stock that is to be purchased by it as provided in the Underwriting Agreement, delivery of such Secondary Stock, as directed by such Underwriter, to Cede & Co. or such other nominee as may be designated by The Depository Trust Company (“DTC”), registration of such Secondary Stock in the name of Cede & Co. or such other nominee and the crediting of such Secondary Stock on the records of DTC to a “securities account” (as defined in Section 8-501 of the Uniform Commercial Code as in effect in the State of New York (the “NY UCC”)) of such Underwriter with DTC under Section 8-501 of the NY UCC, (A) DTC shall be a “protected purchaser”, within the meaning of Section 8-303 of the NY UCC, of such Secondary Stock, (B) under Section 8-501 of the NY UCC, such Underwriter will acquire a “security entitlement” (as defined in Section 8-102 of the NY UCC) in respect of the Secondary Stock so purchased by it and (C) no action based on any “adverse claim”, within the meaning of Section 8-102 of the NY UCC, to such Secondary Stock may be asserted against such Underwriter with respect to such security entitlement.

     The opinion of counsel described above shall be rendered to the Underwriters at the request of the Selling Stockholders and shall so state therein.

Annex B-3

[Form of Opinion of Local Counsel For
The Chase Selling Stockholders]

     (   ) The Underwriting Agreement has been duly authorized, executed and delivered by or on behalf of each of the Selling Stockholders.

     (   ) A Power of Attorney and a Custody Agreement have been duly authorized, executed and delivered by each Selling Stockholder.

     The opinion of counsel described above shall be rendered to the Underwriters at the request of the Selling Stockholders and shall so state therein.

Annex C

Time of Sale Information

     Free Writing Prospectus as set forth on Annex D

Annex D

Concho Resources Inc.

Pricing Term Sheet

[TO COME]

Exhibit A

_________, 2007

J.P. MORGAN SECURITIES INC.
BANC OF AMERICA SECURITIES LLC
As Representatives of
the several Underwriters listed in
Schedule I to the Underwriting
Agreement referred to below
c/o J.P. Morgan Securities Inc.
277 Park Avenue
New York, NY 10172

Re:      Concho Resources Inc. — Public Offering

Ladies and Gentlemen:

     The undersigned understands that you, as Representatives of the several Underwriters, propose to enter into an Underwriting Agreement (the “Underwriting Agreement”) with Concho Resources Inc., a Delaware corporation (the “Company”), and the Selling Stockholders to be named therein, providing for the public offering (the “Public Offering”) by the several Underwriters to be named in Schedule I to the Underwriting Agreement (the “Underwriters”) of common stock, par value $0.001 per share, of the Company (the “Securities”).

     In consideration of the Underwriters’ agreement to purchase and make the Public Offering of the Securities, and for other good and valuable consideration receipt of which is hereby acknowledged, the undersigned hereby agrees that, without the prior written consent of J.P. Morgan Securities Inc. and Banc of America Securities LLC, on behalf of the Underwriters, the undersigned will not, during the period ending 90 days after the date of the prospectus relating to the Public Offering (the “Prospectus”), (1) offer, pledge, announce the intention to sell, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock, par value $0.001 per share, of the Company (the “Common Stock”) or any securities convertible into or exercisable or exchangeable for Common Stock (including, without limitation, Common Stock which may be deemed to be beneficially owned by the undersigned in accordance with the rules and regulations of the Securities and Exchange Commission and securities which may be issued upon exercise of a stock option or warrant) or (2) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise or (3) make any demand for or exercise any right with respect to the registration of any shares of Stock or any security convertible into or exercisable or exchangeable for Stock without the prior written consent of the Representatives, in each case other than (A) the Securities to be sold by the undersigned pursuant to the Underwriting Agreement, (B) transfers of shares of Common Stock as a bona fide gift or gifts, including to the Chase Foundation, (C) transfers of shares of Common Stock or other securities to directors, officers or employees of Chase Oil Corporation or its subsidiaries or affiliates and (D) distributions of shares of Common Stock to members or stockholders of the undersigned; provided that in the case of any transfer or distribution pursuant to clause (B), (C), or (D) each donee, transferee or distributee shall execute and deliver to the Representatives a lock-up letter in the form of this paragraph; and provided, further, that in the case of any transfer or distribution pursuant to clause (B) or (D), no filing by any party (donor, donee,

transferor or transferee) under Section 16(a) of the Securities Exchange Act of 1934, as amended, shall be required or shall be made voluntarily in connection with such transfer or distribution (other than a filing on a Form 5).

     Notwithstanding the foregoing, if (1) during the last 17 days of the 90-day restricted period, the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the 90-day restricted period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the 90-day period, the restrictions imposed by this Letter Agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event; provided, however, that in no event shall such restrictions extend past 124 days from the date of the Prospectus.

     In furtherance of the foregoing, the Company, and any duly appointed transfer agent for the registration or transfer of the securities described herein, are hereby authorized to decline to make any transfer of securities if such transfer would constitute a violation or breach of this Letter Agreement.

     The undersigned hereby represents and warrants that the undersigned has full power and authority to enter into this Letter Agreement. All authority herein conferred or agreed to be conferred and any obligations of the undersigned shall be binding upon the successors, assigns, heirs or personal representatives of the undersigned.

     The undersigned understands that, if the Underwriting Agreement does not become effective, or if the Underwriting Agreement (other than the provisions thereof which survive termination) shall terminate or be terminated prior to payment for and delivery of the Securities to be sold thereunder, the undersigned shall be released form all obligations under this Letter Agreement.

     The undersigned understands that to the extent the Underwriters enter into the Underwriting Agreement and proceed with the Public Offering, they will be doing so in reliance upon this Letter Agreement.

     This Letter Agreement shall be governed by and construed in accordance with the laws of the State of New York, without regard to the conflict of laws principles thereof.