TERMINATION ANDRELEASE OF IRREVOCABLE CONTRACT GUARANTEE

Exhibit 10.21

TERMINATION AND RELEASE OF IRREVOCABLE CONTRACT GUARANTEE

THIS TERMINATION AND RELEASE OF IRREVOCABLE CONTRACT GUARANTEE (this “Release”) is made and entered into as of [•] [•], 2009, by and among C/R Cobalt Investment Partnership, L.P., C/R Energy Coinvestment II, L.P., Riverstone Energy Coinvestment III, L.P., C/R Energy III Cobalt Partnership, L.P., Carlyle/Riverstone Global Energy and Power Fund III, L.P., Carlyle Energy Coinvestment III, L.P., First Reserve Fund XI, L.P., FR XI Onshore AIV, L.P., GS Capital Partners VI Fund, L.P., GS Capital Partners VI Offshore Fund, L.P., GS Capital Partners V Fund, L.P., GS Capital Partners V Offshore Fund, L.P., KERN Energy Partners I LP, KERN Energy Partners I U.S., LP, KERN Energy Partners II LP, KERN Energy Partners II U.S., LP, Caisse de Dépôt et Placement du Québec, and The Board of Trustees of the Leland Stanford Junior University (each a “Guarantor” and collectively, the “Guarantors”) and ENSCO Offshore Company, a Delaware corporation (the “Contractor”).

W I T N E S S E T H:

WHEREAS, the Guarantors entered into that certain Irrevocable Contract Guarantee, dated as of May 5, 2008 (the “Guarantee”), in favor of the Contractor, pursuant to which, as a condition to the Contractor’s entry into that certain Offshore Daywork Drilling Contract, dated as of May 5, 2008 (the “Rig Agreement”),  with Cobalt International Energy, L.P. (the “Partnership”), the Guarantors guaranteed certain payment obligations of the Partnership to the Contractor under the Rig Agreement (any and all obligations of each Guarantor under the Guarantee, the “Obligations”);

WHEREAS, the Partnership is proposing to effect the sale of shares of common stock of a newly formed corporation, that will wholly own the Partnership, to the public in an initial public offering (the “IPO”);

WHEREAS, pursuant to Section 8 of the Guarantee, each Guarantor is required to be released from the Guarantee and its Obligations upon receipt by the Contractor of reasonable substitute credit support reasonably acceptable to the Contractor in the amount of the remaining Obligations of such Guarantor;

WHEREAS, effective as of the date hereof, the Partnership has obtained [•] to provide a credit support for the remaining Obligations of all the Guarantors (the “Substitute Credit Support”);

WHEREAS, the Contractor agrees and acknowledges that the Substitute Credit Support is a reasonable substitute credit support for the remaining Obligations as required pursuant to Section 8 of the Guarantee; and

WHEREAS, the Contractor hereby agrees to release the Guarantors from their Obligations under the Guarantee and terminate the Guarantee , effective as of the date hereof, on the terms set forth in this Release.

NOW, THEREFORE, for good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

1.             Release.  In consideration of the receipt by the Contractor of the Substitute Credit Support, as of the date hereof, the Contractor (on behalf of itself and its successors and assigns) hereby fully and forever releases, discharges and acquits each of the Guarantors (and their respective subsidiaries, affiliates, past and present officers, directors, partners, attorneys, employees, agents, and each of their assigns and their respective predecessors and successors in interest) from the Guarantee and its Obligations (including any and all obligations, liabilities, claims, demands, actions, covenants, and debts of any kind or nature arising out of or relating to the Guarantee).

2.             Termination.  The Guarantee is hereby terminated as of the date hereof and, upon such termination, the Guarantors shall have no further liabilities or obligations thereunder.

3.             Entire Agreement.  This Release contains the complete, exclusive and final agreement between the Contractor and the Guarantors and supersedes any and all prior agreements, arrangements or understandings between the Contractor and the Guarantors relating to the subject matter hereof.  No oral understandings, statements, promises or inducements contrary to the terms of this Release exist.  This Release may be modified only upon the written agreement of the Contractor and the Guarantors.

4.             Counterparts.  This Release may be executed by facsimile or in one or more counterparts, all of which together shall constitute one and the same agreement.

5.             Governing Law.  This Release and the rights and obligations of the parties hereto shall be governed by and construed and enforced in accordance with the laws of the State of New York excluding any conflict-of-laws rule or principle (whether of New York or any other jurisdiction) that might refer the governance or the construction of this Release to the law of another jurisdiction.

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IN WITNESS WHEREOF, the parties hereto have caused this Release to be executed as of the date set forth above.

[Signature Page to Termination and Release of Irrevocable Contract Guarantee]

[Signature Page to Termination and Release of Irrevocable Contract Guarantee]

[Signature Page to Termination and Release of Irrevocable Contract Guarantee]

[Signature Page to Termination and Release of Irrevocable Contract Guarantee]

[Signature Page to Termination and Release of Irrevocable Contract Guarantee]

[Signature Page to Termination and Release of Irrevocable Contract Guarantee]