THIRD AMENDMENT TO CREDIT AGREEMENT

Exhibit 10.1

Execution Version

T HIRD A MENDMENT

TO

C REDIT A GREEMENT

AMONG

R EX E NERGY C ORPORATION ,

as Borrower,

K EY B ANK N ATIONAL A SSOCIATION ,

as Administrative Agent,

and

The Lenders Signatory Hereto

Effective as of April 20, 2009

T HIRD A MENDMENT TO C REDIT A GREEMENT

This T HIRD A MENDMENT TO C REDIT A GREEMENT (this “ Third Amendment ”) executed effective as of the 20th of April, 2009 (the “ Third Amendment Effective Date ”) is among R EX E NERGY C ORPORATION , a corporation formed under the laws of the State of Delaware (the “ Borrower ”); K EY B ANK N ATIONAL A SSOCIATION , as administrative agent for the Lenders (in such capacity, together with its successors, the “ Administrative Agent ”), and the Lenders signatory hereto.

Recitals

A. The Borrower, the Administrative Agent and the Lenders are parties to that certain Credit Agreement dated as of September 28, 2007, as amended by that certain First Amendment dated as of April 14, 2008, as amended by that certain Second Amendment dated as of December 23, 2008 (the “ Credit Agreement ”), pursuant to which the Lenders have made certain credit available to and on behalf of the Borrower.

B. The Borrower, the Administrative Agent and the Lenders have agreed to amend certain provisions of the Credit Agreement.

C. The Lenders have redetermined the Borrowing Base in the amount set forth herein.

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

Section 1. Defined Terms . Each capitalized term which is defined in the Credit Agreement, but which is not defined in this Third Amendment, shall have the meaning ascribed such term in the Credit Agreement. Unless otherwise indicated, all section references in this Third Amendment refer to the Credit Agreement.

Section 2. Amendments to Credit Agreement .

2.1 Amendments to Section 1.02 . Section 1.02 is hereby amended by deleting the defined term “Applicable Margin” and replacing it with the following:

“‘ Applicable Margin ’ means, for any day, with respect to any ABR Loan or Eurodollar Loan, or with respect to the Commitment Fee Rate, as the case may be, the rate per annum set forth in the Borrowing Base Utilization Grid below based upon the Borrowing Base Utilization Percentage then in effect:

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Each change in the Applicable Margin shall apply during the period commencing on the effective date of such change and ending on the date immediately preceding the effective date of the next such change, provided, however, that if at any time the Borrower fails to deliver a Reserve Report pursuant to Section 8.12(a), then the “ Applicable Margin ” means the rate per annum set forth on the grid when the Borrowing Base Utilization Percentage is at its highest level until the day that such Reserve Report is delivered to the Administrative Agent, and as of such delivery date and until the effective date of the next change in the Applicable Margin, the Applicable Margin shall be based on the Borrowing Base reflected by such Reserve Report.”

Section 3. Borrowing Base .

3.1. Borrowing Base . Pursuant to Section 2.07 of the Credit Agreement, the Borrowing Base is hereby maintained at $80,000,000 until the next Redetermination Date, subject to further adjustments from time to time pursuant to Section 8.13(c) or Section 9.12.

Section 4. Conditions Precedent . The effectiveness of this Third Amendment is subject to the receipt by the Administrative Agent of the following documents and satisfaction of the other conditions provided in this Section 4, each of which shall be reasonably satisfactory to the Administrative Agent in form and substance:

4.1 Third Amendment . The Administrative Agent shall have received multiple counterparts as requested of this Third Amendment from the Borrower and each Lender.

4.2 Payment of Outstanding Invoices . Payment by the Borrower to the Administrative Agent of all fees and other amounts due and payable on or prior to the Third Amendment Effective Date, including, to the extent invoiced, reimbursement or payment of all out-of-pocket expenses required to be reimbursed or paid by the Borrower.

4.3 No Default . No Default or Event of Default shall have occurred and be continuing as of the Third Amendment Effective Date.

Section 5. Representations and Warranties; Etc. The Borrower hereby affirms: (a) that as of the date of execution and delivery of this Third Amendment, all of the representations and warranties contained in each Loan Document to which the Borrower is a party are true and correct in all material respects as though made on and as of the Third Amendment Effective Date (unless made as of a specific earlier date, in which case, was true as of such date); and (b) that after giving effect to this Third Amendment and to the transactions contemplated hereby, no Defaults exist under the Loan Documents or will exist under the Loan Documents.

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Section 6. Miscellaneous .

6.1 Confirmation . The provisions of the Credit Agreement (as amended by this Third Amendment) shall remain in full force and effect in accordance with its terms following the effectiveness of this Third Amendment.

6.2 Ratification and Affirmation of the Borrower . The Borrower hereby expressly (a) acknowledges the terms of this Third Amendment, (b) ratifies and affirms its obligations under the Credit Agreement and the other Security Instruments to which it is a party, and (c) acknowledges, renews and extends its continued liability under the Credit Agreement and the other Security Instruments