[Form of Letter Agreement of GHL Acquisition Corp. with Greenhill & Co., Inc.]

Exhibit 10.1

[Form of Letter Agreement of GHL Acquisition Corp. with

Greenhill & Co., Inc.]

, 2008

GHL Acquisition Corp.

300 Park Avenue, 23^rd Floor

New York, NY 10022

Re: Initial Public Offering of GHL Acquisition Corp. (the “Company”)

Ladies and Gentlemen:

This letter is being delivered to you in connection with an underwritten initial public offering (the “IPO”) of the Company’s units (the “Units”), each consisting of one share of the Company’s common stock, par value $0.001 per share (the “Common Stock”), and one warrant exercisable for one share of Common Stock (each, a “Warrant”). Certain capitalized terms used herein are defined in paragraph 9 hereof.

In consideration of the Company proceeding with the IPO and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the undersigned hereby acknowledges and agrees with the Company as follows:

1. (a) Neither the undersigned nor any affiliate of the undersigned will be entitled to receive, and no such person will accept, any finder’s fee, reimbursement, cash payment or other compensation from the Company for services rendered to the Company prior to or in connection with the consummation of an Initial Business Combination, other than (subject to the following sentence) (i) repayment of that certain Promissory Note in the amount of $250,000 (and accrued interest thereon) made to the Company by the undersigned to cover offering-related and organizational expenses; (ii) a payment of an aggregate of $10,000 per month to the undersigned, for office space, secretarial and administrative services; and (iii) reimbursement for any out-of-pocket expenses or advances related to the IPO and identifying, investigating and consummating an Initial Business Combination. The Company’s Audit Committee will review and approve all payments made to the undersigned and its affiliates, other than the payment described in clause (ii) in the immediately preceding sentence.

(b) Neither the undersigned nor any affiliate of the undersigned will be entitled to receive, and no such person will accept, a finder’s fee, consulting fee or any other similar fees from any other person or entity in connection with an Initial Business Combination, other than compensation or fees that may be received for any services provided following such Initial Business Combination.

(c) The Company will not consummate any Initial Business Combination with any entity in which any of the Company’s initial stockholders, officers or directors or their affiliates has a material ownership interest or in which a merchant banking fund advised by Greenhill or an affiliate of Greenhill has a material ownership interest.

2. In connection with any proposed Initial Business Combination and an amendment to the Company’s amended and restated certificate of incorporation to provide for the Company’s perpetual existence, the Company submits to its stockholders for approval, the undersigned shall vote the Founder’s Shares owned by it in accordance with the majority of the shares of Common Stock voted by the Company’s Public Stockholders and the Founder shall vote all shares of Common Stock that it may acquire in the IPO or in the secondary market in favor of (x) the Initial Business Combination and (y) an amendment to the Company’s amended and restated certificate of incorporation to provide for the Company’s perpetual existence.

3. The Founder hereby (a) waives, with respect to the Founder’s Shares owned by it any and all right, title, interest or claim of any kind in or to any distributions of the Trust Account or to any other amounts distributed in connection with a liquidating distribution of the Company, including any conversion rights with respect to such Founder’s Shares, in the event that the Company does not consummate an Initial Business Combination and (b) agrees that the Company shall be entitled to reimbursement from the Founder for any such distribution of the Trust Account or any other such amounts distributed in connection with a liquidating distribution of the Company received by it with respect to its Founder’s Shares in the event that the Company does not consummate an Initial Business Combination.

4. Until the earlier to occur of the Initial Business Combination or the liquidation of the Trust Account, the undersigned shall indemnify and hold harmless the Company against any and all losses, liabilities, claims, damages and expenses whatsoever (including, but not limited to, any and all legal or other expenses reasonably incurred in investigating, preparing or defending against any litigation, whether pending or threatened, or any claim whatsoever) to which the Company may become subject, but only if, and to the extent that (a) the claims reduce the amounts in the Trust Account available for payment to holders of the IPO Shares in the event of a liquidation of the Trust Account, and (b) the claims are made by (i) a vendor for services rendered or products sold to us, (ii) by a third party with which the Company entered into a contractual relationship following consummation of the IPO or (iii) by a prospective target business; provided that such indemnity shall not apply to (x) any claimed amounts owed to a third party that executed a waiver of any right, title, interest or claim of any kind in or to the Trust Account, or (y) as to any claims under the Company’s obligation to indemnify the Underwriters against certain liabilities, including liabilities under the Securities Act of 1933, as amended.

5. The Founder’s questionnaire for directors, officers and principal stockholders furnished to the Company and the Underwriters is true and accurate in all respects. The undersigned represents and warrants that:

(a) the undersigned is not subject to or a respondent in any legal action for, any injunction, cease-and-desist order or order or stipulation to desist or refrain from any act or practice relating to the offering of securities in any jurisdiction;

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(b) the undersigned has never been convicted of or pleaded guilty to any crime (i) involving any fraud or (ii) relating to any financial transaction or handling of funds of another person, or (iii) pertaining to any dealings in any securities and the undersigned is not currently a defendant in any such criminal proceeding; and

(c) the undersigned has never been suspended or expelled from membership in any securities or commodities exchange or association or had a securities or commodities license or registration denied, suspended or revoked.

6. The undersigned has full right and power, without violating any agreement by which it is bound, to enter into this letter agreement, and hereby consents to being named in the Registration Statement.

7. The undersigned shall not, without the prior consent of the Company:

(a) offer, sell, contract to sell, pledge, hypothecate, grant any option to purchase or otherwise dispose of (or enter into any transaction which is designed to, or might reasonably be expected to, result in the disposition (whether by actual disposition or effective economic disposition due to cash settlement or otherwise) by the undersigned or any affiliate of the undersigned or any person in privity with the undersigned or any affiliate of the undersigned), directly or indirectly, including the participation in the filing of a registration statement with the Securities and Exchange Commission (other than in accordance with the Registration Rights Agreement) in respect of;

(b) establish or increase a put equivalent position or liquidate or decrease a call equivalent position within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, and the rules and regulations of the Securities and Exchange Commission promulgated thereunder, with respect to; or

(c) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of, or any securities convertible into or exercisable or exchangeable for, or other rights to purchase, whether any such transaction is to be settled by delivery of Common Stock or such other securities, in cash or otherwise, any Securities, or publicly announce an intention to effect any such transaction:

(i) its Founder’s Securities, for a period of 180 days from the date the Company completes its Initial Business Combination or earlier in the event that subsequent to the consummation of the Initial Business Combination (x) the last sales price of the Common Stock equals or exceeds $14.25 per share for any 20 trading days within any 30-trading day period commencing 90 days after the date of the consummation of such Initial Business Combination or (y) the Company consummates a liquidation, merger, stock exchange or other similar transaction which results in all of the Company’s stockholders having the right to exchange their shares of Common Stock for cash, securities or other property, and

(ii) its Private Placement Securities, after the Company completes its Initial Business Combination.

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The Founder acknowledges and agrees that the foregoing transfer restrictions hereby supersede the transfer restrictions set forth in Section 1(C)(v) of the Founder’s Securities Purchase Agreement with respect to the Founder’s Securities; provided, however, that the Founder may, at any time, transfer its Founder’s Securities to Permitted Transferees and transfer its Founder’s Warrants and Private Placement Securities in accordance with the Founder’s Securities Purchase Agreement and Warrant Agreement.

8. The undersigned represents and warrants that:

(a) the Founder’s Securities Purchase Agreement has been duly authorized, executed and delivered by the Founder, is a valid and binding agreement of the Founder, enforceable against the Founder in accordance with its terms except as the enforceability thereof may be limited by bankruptcy, insolvency, or similar laws affecting creditors’ rights generally from time to time in effect and by equitable principles of general applicability;

(b) the Registration Rights Agreement has been duly authorized, and upon execution and delivery by the parties thereto, will be a valid and binding agreement of the Founder, enforceable against the Founder in accordance with its terms except as the enforceability thereof may be limited by bankruptcy, insolvency, or similar laws affecting creditors’ rights generally from time to time in effect and by equitable principles of general applicability;

(c) the Securities Purchase Agreement has been duly authorized, executed and delivered by the Founder and is a valid and binding agreement of the Founder, enforceable against it in accordance with its terms except as the enforceability thereof may be limited by bankruptcy, insolvency, or similar laws affecting creditors’ rights generally from time to time in effect and by equitable principles of general applicability;

(d) this letter agreement has been duly authorized, executed and delivered by the undersigned and is a valid and binding agreement of the Founder, enforceable against it in accordance with its terms except as the enforceability thereof may be limited by bankruptcy, insolvency, or similar laws affecting creditors’ rights generally from time to time in effect and by equitable principles of general applicability;

(e) the Administrative Services Letter Agreement has been duly authorized, executed and delivered by the undersigned and is a valid and binding agreement of the undersigned, enforceable against the Founder in accordance with its terms except as the enforceability thereof may be limited by bankruptcy, insolvency, or similar laws affecting creditors’ rights generally from time to time in effect and by equitable principles of general applicability; and

(f) the Non-Compete Agreement has been duly authorized, executed and delivered by the Founder, and is a valid and binding agreement of the Founder, enforceable against the Founder in accordance with its terms except as the enforceability thereof may be limited by bankruptcy, insolvency, or similar laws affecting creditors’ rights generally from time to time in effect and by equitable principles of general applicability.

9. As used herein:

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(a) “Administrative Services Letter Agreement” shall mean an administrative services letter agreement, dated November 27, 2007, entered into by and between the Company and Greenhill relating to the use of office space, secretarial and administrative services.

(b) “Founder’s Securities” shall mean the 9,775,000 units of the Company (the “Founder’s Units”), each consisting of one share of Common Stock (the “Founder’s Shares”) and one warrant to purchase one share of Common Stock (including the underlying shares of Common Stock) (the “Founder’s Warrants”), initially issued to the Founder pursuant to the Founder’s Securities Purchase Agreement and subject to adjustment pursuant thereto, including any securities of the Company issued as a dividend or other distribution with respect to or in exchange for or in replacement of any of the foregoing securities.

(c) “Founder’s Securities Purchase Agreement” shall mean the agreement between the Founder and the Company, dated as of November 12, 2007 relating to the purchase by the Founder of the Founder’s Securities.

(d) “Greenhill” shall mean collectively, Greenhill & Co., Inc. and its affiliates.

(e) “Initial Business Combination” shall mean a merger, capital stock exchange, asset acquisition, stock purchase, reorganization or other similar business combination with one or more businesses or assets, which will require that a majority of the shares of common stock voted by the public stockholders present in person or by proxy at a duly held stockholders meeting are voted in favor of our initial business combination, a majority of the outstanding shares of our common stock are voted in favor of the amendment to our amended and restated certificate of incorporation to provide for our perpetual existence and not more than 30% of the shares (minus one share) sold in this offering are voted against the proposed initial business combination and exercise their conversion rights.

(f) “IPO Shares” shall mean the shares of Common Stock underlying the Units issued in the IPO.

(g) “Permitted Transferee” shall mean (i) any executive officer, director or employee of the Company; or (ii) any person or entity affiliated or entity associated or affiliated with Greenhill, in each case that agree in writing to be bound by the transfer restrictions and voting, waiver of liquidation rights and adjustment provisions set forth in the Founder’s Securities Purchase Agreement, Warrant Agreement and herein applicable to the Securities being transferred.

(h) “Private Placement Securities” shall mean the 8,000,000 warrants of the Company (the “Private Placement Warrants”), each to purchase one share of Common Stock (including the underlying shares of Common Stock) issued to the Founder pursuant to the Founder’s Securities Purchase Agreement.

(i) “Promissory Note” shall mean the unsecured promissory note of the Company to Greenhill in the original principal amount of $250,000 due the earlier of December 30, 2008 or the consummation of the IPO.

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(j) “Public Stockholders” shall mean purchasers of shares of Common Stock in the IPO or in the secondary market, including any of the Company’s officers or directors or their affiliates and the undersigned, to the extent that they purchase shares of Common Stock in the IPO or the secondary market.

(k) “Registration Rights Agreement” shall mean the Registration Rights Agreement, dated as of the date hereof, entered into by and among the Company and the investors named on the signature pages thereto.

(l) “Registration Statement” shall mean the Company’s Registration Statement on Form S-1 (File No. 333-147722, originally filed by the Company with the Securities and Exchange Commission under the Securities Act of 1933, as amended, on [  ], 2008) in the form it became effective and including the information deemed to be a part thereof at the time of effectiveness pursuant to Rule 430A under the Securities Act of 1933, as amended.

(m) “Non-Compete Agreement” shall mean the Non-Compete Agreement, dated as of [  ], 2008, entered into between the Company, its executive officers and Greenhill.

(n) “Securities” shall mean the Founder’s Securities and the Private Placement Securities, including any securities of the Company issued as a dividend or other distribution with respect to or in exchange for or in replacement of any of the foregoing securities.

(o) “Securities Purchase Agreement” shall mean the Securities Purchase Agreement, dated [  ], entered into by and among the Founder and each of Thomas C. Canfield, Kevin P. Clarke and Parker W. Rush.

(p) “Underwriters” shall mean the underwriters named in Schedule I to the Underwriting Agreement entered into by and between the Company and Banc of America Securities LLC, as representative of such underwriters, in connection with the IPO.

(q) “Trust Account” shall mean the trust account established under the Investment Management Trust Agreement, dated as of the date hereof, by and between the Company and American Stock Transfer & Trust Company, as Trustee.

(r) “Warrant Agreement” shall mean the agreement between the Company and American Stock Transfer & Trust Company, as Warrant Agent, dated as November 12, 2007.

The undersigned acknowledges and understands that the Company and the Underwriters will rely upon the agreements, representations and warranties set forth herein in proceeding with the IPO. Nothing contained herein shall be deemed to render the Underwriters a representative of, or a fiduciary with respect to, the Company, its stockholders, or any creditor or vendor of the Company with respect to the subject matter hereof.

This letter agreement shall be binding on the undersigned and such person’s successors, heirs, personal representatives and assigns. This letter agreement shall terminate on the earlier of (i) the consummation of an Initial Business Combination and (ii) the distribution to the Public

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Stockholders of the Trust Account and liquidation of the Company; provided that such termination shall not relieve the undersigned from liability for any breach of this agreement prior to its termination, and provided further that paragraph 4 of this agreement shall survive a termination.

This letter agreement shall be governed by and interpreted and construed in accordance with the laws of the State of New York applicable to contracts formed and to be performed entirely within the State of New York, without regard to the conflicts of law provisions thereof to the extent such principles or rules would require or permit the application of the laws of another jurisdiction.

No term or provision of this letter agreement may be amended, changed, waived, altered or modified except by written instrument executed and delivered by the party against whom such amendment, change, waiver, alteration or modification is to be enforced.

[Signature Page Follows]

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[Signature Page to Letter Agreement for Founder and the Company]

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