ASSIGNMENT, ASSUMPTION AND RATIFICATION AGREEMENT

Exhibit 10.25

ASSIGNMENT, ASSUMPTION AND RATIFICATION AGREEMENT

THIS ASSIGNMENT, ASSUMPTION AND RATIFICATION AGREEMENT (this “ Agreement ”) is made and entered into effective as of the 25th day of July, 2007 (the “ Effective Date ”), by and between AMVEST Osage, Inc. (the “ Assignor ”), and CEP Mid-Continent LLC (the “Assignee”).

WITNESSETH:

WHEREAS , Assignor desires to sell, assign and transfer to Assignee all of its interest, rights, duties and obligations under the Exploration and Development Agreement dated July 25, 2005, as amended, by and between Assignor and the Osage Tribe of Indians of Oklahoma (the “Exploration and Development Agreement”), and Assignee desires to accept said sale, assignment and transfer upon the terms and conditions hereinafter set forth;

NOW THEREFORE , in consideration of the premises and of the mutual covenants and agreements contained herein, and other good and valuable consideration. the receipt and sufficiency of which are hereby acknowledged, the parties hereto covenant and agree as follows:

1. Assignment . Assignor hereby sells, assigns and transfers to Assignee its interests, rights, duties and obligations under the Exploration and Development Agreement with respect to the interest and lands set forth in the Exploration and Development Agreement (the “ Interests ”).

2. Acceptance, Ratification and Indemnification . Assignee hereby accepts the foregoing sale, assignment and transfer and promises to faithfully perform all other covenants, stipulations, agreements and obligations under the Exploration and Development Agreement with respect to the interests and ratifies, adopts, and confirms the Exploration and Development Agreement to the same extent as if Assignee had executed the Exploration and Development Agreement. Assignee shall indemnify and save Assignor harmless from any and all obligations, claims, demands, actions, causes of action, suits, proceedings, damages, liabilities, costs or expenses of every nature whatsoever (collectively “ Liabilities ”) which relate to the Interests. The provisions of this Section 2 shall survive the performance of the terms and conditions of this Agreement.

3. Binding Effect . This Agreement shall become effective upon the execution and acknowledgement of all the parties hereto. This Agreement shall be binding upon the respective heirs, personal representatives, successors and assigns of the parties hereto. The parties hereto shall execute and deliver such further and additional instruments, agreements and other documents as may be necessary to evidence or carry out the provision of this Agreement.

4. Entire Agreement . This Agreement supersedes all previously made between the parties hereto relating to its subject matter. There are no other understandings or agreements between them.

5. Notices . All notices or other documents under this Agreement shall be in writing and delivered personally or mailed by certified mail, postage prepaid, addressed to the parties at the following addresses: