GUARANTY AGREEMENT

Exhibit 10.15

GUARANTY AGREEMENT

WHEREAS, the execution of this Guaranty Agreement is a condition to UNION PLANTERS BANK, N.A., a national banking association (“Lender”) making certain loans to GEOSPACE TECHNOLOGIES, LP, a Texas limited partnership (“Geospace”), OYO INSTRUMENTS, LP, a Texas limited partnership (“Instruments”), GEOSPACE ENGINEERING RESOURCES INTERNATIONAL, LP, a Texas limited partnership (“Engineering”), CONCORD TECHNOLOGIES, LP, a Texas limited partnership (“Concord”), and OYOG OPERATIONS, LP, a Texas limited partnership (“Operations” and together with Geospace, Instruments, Engineering and Concord, collectively hereinafter referred to as the “Borrowers”), pursuant to that certain Loan Agreement dated as of November 22, 2004, between Borrowers and Lender (such Loan Agreement as it may hereafter be amended or modified from time to time, is hereinafter referred to as the “Loan Agreement”);

NOW, THEREFORE, for valuable consideration, the receipt and adequacy of which are hereby acknowledged, the undersigned, OYOG LIMITED PARTNER, LLC, a Nevada limited liability company (the “Guarantor”), hereby irrevocably and unconditionally guarantees to Lender the full and prompt payment and performance of the Guaranteed Indebtedness (hereinafter defined). This Guaranty Agreement shall be upon the following terms:

1. The term “Guaranteed Indebtedness”, as used herein means all of the “Obligations”, as defined in the Loan Agreement. The term “Guaranteed Indebtedness” shall include any and all post-petition interest and expenses (including attorneys’ fees) whether or not allowed under any bankruptcy, insolvency, or other similar law. As of the date of this Guaranty Agreement, the Obligations include, but are not limited to the indebtedness evidenced by (a) that certain promissory note in the original principal amount of $15,000,000.00, dated as of November 22, 2004, executed by Borrowers and payable to the order of Lender, and (b) all renewals, extensions, amendments, increases, decreases or other modifications of any of the foregoing and all promissory notes given in renewal, extension, amendment, increase, decrease or other modification thereof.

2. This instrument shall be an absolute, continuing, irrevocable, and unconditional guaranty of payment and performance, and not a guaranty of collection, and Guarantor shall remain liable on its obligations hereunder until the payment and performance in full of the Guaranteed Indebtedness. No set-off, counterclaim, recoupment, reduction, or diminution of any obligation, or any defense of any kind or nature (other than actual payment) which any Borrower may have against Lender or any other party, or which Guarantor may have against any Borrower, Lender, or any other party, shall be available to, or shall be asserted by, Guarantor against Lender or any subsequent holder of the Guaranteed Indebtedness or any part thereof or against payment of the Guaranteed Indebtedness or any part thereof.

3. If Guarantor becomes liable for any indebtedness owing by Borrowers to Lender by endorsement or otherwise, other than under this Guaranty Agreement, such liability shall not be in any manner impaired or affected hereby, and the rights of Lender hereunder shall be cumulative of any and all other rights that Lender may ever have against Guarantor. The exercise by Lender of any right or remedy hereunder or under any other instrument, or at law or in equity, shall not preclude the concurrent or subsequent exercise of any other right or remedy.

4. In the event of default by any Borrower in payment or performance of the Guaranteed Indebtedness, or any part thereof, when such Guaranteed Indebtedness becomes due, whether by its

terms, by acceleration, or otherwise, Guarantor shall promptly pay the amount due thereon to Lender without notice or demand in lawful currency of the United States of America and it shall not be necessary for Lender, in order to enforce such payment by Guarantor, first to institute suit or exhaust its remedies against any Borrower or others liable on such Guaranteed Indebtedness, or to enforce any rights against any collateral which shall ever have been given to secure such Guaranteed Indebtedness. Until the Guaranteed Indebtedness is paid in full and a period of ninety (90) days has passed following such payment, Guarantor waives any and all rights it may now or hereafter have under any agreement or at law or in equity (including, without limitation, any law subrogating the Guarantor to the rights of Lender) to assert any claim against or seek contribution, indemnification or any other form of reimbursement from any Borrower or any other party liable for payment of any or all of the Guaranteed Indebtedness for any payment made by Guarantor under or in connection with this Guaranty Agreement or otherwise.

5. If acceleration of the time for payment of any amount payable by any Borrower under the Guaranteed Indebtedness is stayed upon the insolvency, bankruptcy, or reorganization of any Borrower, all such amounts otherwise subject to acceleration under the terms of the Guaranteed Indebtedness shall nonetheless be payable by Guarantor hereunder forthwith on demand by Lender.

6. Guarantor hereby agrees that its obligations under this Guaranty Agreement shall not be released, discharged, diminished, impaired, reduced, or affected for any reason or by the occurrence of any event, including, without limitation, one or more of the following events, whether or not with notice to or the consent of Guarantor: (a) the taking or accepting of collateral as security for any or all of the Guaranteed Indebtedness or the release, surrender, exchange, or subordination of any collateral now or hereafter securing any or all of the Guaranteed Indebtedness; (b) any partial release of the liability of Guarantor hereunder, or the full or partial release of any other guarantor from liability for any or all of the Guaranteed Indebtedness; (c) any disability of any Borrower, or the dissolution, insolvency, or bankruptcy of any Borrower, Guarantor, or any other party at any time liable for the payment of any or all of the Guaranteed Indebtedness; (d) any renewal, extension, modification, waiver, amendment, or rearrangement of any or all of the Guaranteed Indebtedness or any instrument, document, or agreement evidencing, securing, or otherwise relating to any or all of the Guaranteed Indebtedness; (e) any adjustment, indulgence, forbearance, waiver, or compromise that may be granted or given by Lender to any Borrower, Guarantor, or any other party ever liable for any or all of the Guaranteed Indebtedness; (f) any neglect, delay, omission, failure, or refusal of Lender to take or prosecute any action for the collection of any of the Guaranteed Indebtedness or to foreclose or take or prosecute any action in connection with any instrument, document, or agreement evidencing, securing, or otherwise relating to any or all of the Guaranteed Indebtedness; (g) the unenforceability or invalidity of any or all of the Guaranteed Indebtedness or of any instrument, document, or agreement evidencing, securing, or otherwise relating to any or all of the Guaranteed Indebtedness; (h) any payment by Borrower or any other party to Lender is held to constitute a preference under applicable bankruptcy or insolvency law or if for any other reason Lender is required to refund any payment or pay the amount thereof to someone else; (i) the settlement or compromise of any of the Guaranteed Indebtedness; (j) the non-perfection of any security interest or lien securing any or all of the Guaranteed Indebtedness; (k) any impairment of any collateral securing any or all of the Guaranteed Indebtedness; (l) the failure of Lender to sell any collateral securing any or all of the Guaranteed Indebtedness in a commercially reasonable manner or as otherwise required by law; (m) any change in the existence, structure, or ownership of any Borrower; or (n) any other circumstance (other than actual payment) which might otherwise constitute a defense available to, or discharge of, any Borrower or Guarantor.

7. Guarantor represents and warrants to Lender as follows:

1. Guarantor is a limited liability company duly organized, validly existing and in good standing under the laws of the state of its organization, is qualified to do business in all jurisdictions in which the nature of the business conducted by it makes such qualification necessary and where failure to so qualify might reasonably be expected to have a material adverse effect on its business, financial condition, or operations.

2. Guarantor has the power, authority and legal right to execute, deliver, and perform its obligations under this Guaranty Agreement and this Guaranty Agreement constitutes the legal, valid, and binding obligation of Guarantor, enforceable against Guarantor in accordance with its respective terms, except as limited by (i) bankruptcy, insolvency, or other laws of general application relating to the enforcement of creditor’s rights and (ii) by general principles of equity.

3. The execution, delivery, and performance by Guarantor of this Guaranty Agreement have been duly authorized by all requisite action on the part of Guarantor and do not and will not violate or conflict with the articles of organization or regulations of Guarantor or any law, rule, or regulation or any order, writ, injunction or decree of any court, governmental authority or agency, or arbitrator and do not and will not conflict with, result in a breach of, or constitute a default under, or result in the imposition of any lien upon any assets of Guarantor pursuant to the provisions of any indenture, mortgage, deed of trust, security agreement, franchise, permit, license, or other instrument or agreement to which Guarantor or its properties is bound.

4. No authorization, approval, or consent of, and no filing or registration with, any court, governmental authority, or third party is necessary for the execution, delivery or performance by Guarantor of this Guaranty Agreement or the validity or enforceability thereof.

5. The value of the consideration received and to be received by Guarantor as a result of Borrowers and Lender entering into the Loan Agreement and Guarantor executing and delivering this Guaranty Agreement is reasonably worth at least as much as the liability and obligation of Guarantor hereunder, and such liability and obligation and the Loan Agreement have benefitted and may reasonably be expected to benefit Guarantor directly or indirectly.

6. Guarantor represents and warrants to Lender that Guarantor is not insolvent, Guarantor’s assets exceed its liabilities, and Guarantor will not be rendered insolvent by the execution and performance of this Agreement and the Loan Documents.

8. Guarantor covenants and agrees that, as long as the Guaranteed Indebtedness or any part thereof is outstanding or Lender has any commitment under the Loan Agreement:

1. Guarantor will comply with all of the covenants contained in the Loan Agreement with which Borrowers agree in the Loan Agreement to cause Guarantor to comply as if Guarantor were a party to the Loan Agreement, and all of such covenants are incorporated herein by reference as if set forth herein in full.

2. Guarantor will furnish promptly to Lender written notice of the occurrence of any default under this Guaranty Agreement or an Event of Default under the Loan Agreement of which Guarantor has knowledge.

3. Guarantor will furnish promptly to Lender such additional information concerning Guarantor as Lender may reasonably request.

9. Upon the occurrence of an Event of Default (as defined in the Loan Agreement) Lender shall have the right to set off and apply against this Guaranty Agreement or the Guaranteed Indebtedness or both, at any time and without notice to Guarantor, any and all deposits (general or special, time or demand, provisional or final) or other sums at any time credited by or owing from Lender to Guarantor whether or not the Guaranteed Indebtedness is then due and irrespective of whether or not Lender shall have made any demand under this Guaranty Agreement. In addition to Lender’s right of setoff and as further security for this Guaranty Agreement and the Guaranteed Indebtedness, Guarantor hereby grants Lender a security interest in all deposits (general or special, time or demand, provisional or final) and all other accounts of Guarantor now or hereafter on deposit with or held by Lender and all other sums at any time credited by or owing from Lender to Guarantor. The rights and remedies of Lender hereunder are in addition to other rights and remedies (including, without limitation, other rights of setoff) which Lender may have.

10. Guarantor hereby agrees that the Subordinated Indebtedness (as hereinafter defined) shall be subordinate and junior in right of payment to the prior payment in full of all Guaranteed Indebtedness, and Guarantor hereby assigns the Subordinated Indebtedness to Lender as security for the Guaranteed Indebtedness. If any sums shall be paid to Guarantor by any Borrower or any other person or entity on account of the Subordinated Indebtedness, such sums shall be held in trust by Guarantor for the benefit of Lender and shall forthwith be paid to Lender without affecting the liability of Guarantor under this Guaranty Agreement. For purposes of this Guaranty Agreement, the term “Subordinated Indebtedness” means all indebtedness, liabilities, and obligations of any Borrower to Guarantor, whether such indebtedness, liabilities, and obligations now exist or are hereafter incurred or arise, or whether the obligations of any Borrower thereon are direct, indirect, contingent, primary, secondary, several, joint and several, or otherwise, and irrespective of the person or persons in whose favor such indebtedness, obligations, or liabilities may, at their inception, have been, or may hereafter be created, or the manner in which they have been or may hereafter be acquired by Guarantor.

11. No amendment or waiver of any provision of this Guaranty Agreement or consent to any departure by the Guarantor therefrom shall in any event be effective unless the same shall be in writing and signed by Lender. No failure on the part of Lender to exercise, and no delay in exercising, any right, power, or privilege hereunder shall operate as a waiver thereof; nor shall any single or partial exercise of any right, power, or privilege hereunder preclude any other or further exercise thereof or the exercise of any other right, power, or privilege. The remedies herein provided are cumulative and not exclusive of any remedies provided by law.

12. This Guaranty Agreement is for the benefit of Lender and its successors and assigns, and in the event of an assignment of the Guaranteed Indebtedness, or any part thereof, the rights and benefits hereunder, to the extent applicable to the indebtedness so assigned, may be transferred with such indebtedness. This Guaranty Agreement is binding not only on Guarantor, but on Guarantor’s successors and assigns.

13. Guarantor recognizes that Lender is relying upon this Guaranty Agreement and the undertakings of Guarantor hereunder in making extensions of credit to Borrowers under the Loan Agreement and further recognizes that the execution and delivery of this Guaranty Agreement is a material inducement to Lender in entering into the Loan Agreement. Guarantor hereby acknowledges that there are no conditions to the full effectiveness of this Guaranty Agreement.

14. This Guaranty Agreement is executed and delivered as an incident to a lending transaction negotiated, consummated, and performable in Harris County, Texas, and shall be governed by and construed in accordance with the laws of the State of Texas. Any action or proceeding against Guarantor under or in connection with this Guaranty Agreement may be brought in any state or federal court in Harris County, Texas, and Guarantor hereby irrevocably submits to the nonexclusive jurisdiction of such courts, and waives any objection it may now or hereafter have as to the venue of any such action or proceeding brought in such court. Guarantor agrees that service of process upon it may be made by certified or registered mail, return receipt requested, at its address specified in the Loan Agreement. Nothing herein shall affect the right of Lender to serve process in any other matter permitted by law or shall limit the right of Lender to bring any action or proceeding against Guarantor or with respect to any of Guarantor’s property in courts in other jurisdictions. Any action or proceeding by Guarantor against Lender shall be brought only in a court located in Harris County, Texas.

15. Guarantor shall pay on demand all reasonable attorneys’ fees and all other costs and expenses reasonably incurred by Lender in connection with the preparation, administration, enforcement, or collection of this Guaranty Agreement.

16. Guarantor hereby waives promptness, diligence, notice of any default under the Guaranteed Indebtedness, demand of payment, notice of acceptance of this Guaranty Agreement, presentment, notice of protest, notice of dishonor, notice of the incurring by any Borrower of additional indebtedness, and all other notices and demands with respect to the Guaranteed Indebtedness and this Guaranty Agreement.

17. The Loan Agreement, and all of the terms thereof, are incorporated herein by reference, the same as if stated verbatim herein, and Guarantor agrees that Lender may exercise any and all rights granted to it under the Loan Agreement and the other Loan Documents (as defined in the Loan Agreement) without affecting the validity or enforceability of this Guaranty Agreement. Any notices given hereunder shall be given in the manner provided by and to the addresses set forth in the Loan Agreement.

18. Guarantor hereby represents and warrants to Lender that Guarantor has adequate means to obtain from Borrowers on a continuing basis information concerning the financial condition and assets of Borrowers and that Guarantor is not relying upon Lender to provide (and Lender shall have no duty to provide) any such information to Guarantor either now or in the future.

19. THIS GUARANTY AGREEMENT REPRESENTS THE FINAL, ENTIRE AGREEMENT OF GUARANTOR AND LENDER WITH RESPECT TO GUARANTOR’S GUARANTY OF THE GUARANTEED INDEBTEDNESS AND SUPERSEDES ANY AND ALL PRIOR COMMITMENTS, AGREEMENTS, REPRESENTATIONS, AND UNDERSTANDINGS, WHETHER WRITTEN OR ORAL, RELATING TO THE SUBJECT MATTER HEREOF AND MAY NOT BE CONTRADICTED OR VARIED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OR DISCUSSIONS OR OTHER EXTRINSIC EVIDENCE OF ANY NATURE. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN GUARANTOR AND LENDER. THIS GUARANTY AGREEMENT MAY NOT BE AMENDED EXCEPT IN WRITING BY GUARANTOR AND LENDER.

DATED AND EXECUTED as of November 22, 2004.