AMENDED AND RESTATED CREDIT AGREEMENT

THIRD AMENDMENT

TO

AMENDED AND RESTATED CREDIT AGREEMENT

dated as of

April 29, 2009

among

PIONEER NATURAL RESOURCES COMPANY,

as the Borrower

JPMORGAN CHASE BANK, N.A.

as Administrative Agent

and

The Lenders Party Hereto

____________________________

THIS THIRD AMENDMENT TO AMENDED AND RESTATED CREDIT AGREEMENT (this “ Third Amendment ”) dated as of April 29, 2009, among PIONEER NATURAL RESOURCES COMPANY , a Delaware corporation, as the Borrower, JPMORGAN CHASE BANK , N.A. , as Administrative Agent, and the LENDERS party hereto.

R E C I T A L S

A.          The Borrower, the Administrative Agent, and the Lenders party thereto are parties to that certain Amended and Restated Credit Agreement dated as of April 11, 2007, as amended by that certain First Amendment to Amended and Restated Credit Agreement dated as of November 20, 2007, as further amended by that certain Second Amendment to Amended and Restated Credit Agreement dated as of January 1, 2009 (as further amended, modified, supplemented or restated prior to the date hereof, the “ Credit Agreement ”), pursuant to which the Lenders have made certain credit available to and on behalf of the Borrower.

B.          The Borrower has requested and the Lenders have agreed to amend certain provisions of the Credit Agreement.

C.          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 sections of the Credit Agreement.

(a)         The definition of “ Agreement ” in Section 1.01 of the Credit Agreement is hereby amended in its entirety to read as follows:

“ Agreement ” means this Credit Agreement, as amended by the First Amendment, the Second Amendment and the Third Amendment, as the same may from time to time be amended, modified, supplemented or restated.

(b)       The definition of “ Alternate Base Rate ” in Section 1.01 of the Credit Agreement is hereby amended in its entirety to read as follows:

“ Alternate Base Rate ” means, for any day, a rate per annum equal to the greatest of (a) the Prime Rate in effect on such day, (b) the Federal Funds Effective Rate in effect on such day plus ½ of 1%, or (c) the Adjusted LIBO Rate for a one month Interest Period on such day (or if such day is not a Business Day, the immediately preceding Business Day) plus 1%, provided that, for the avoidance of doubt, the Adjusted LIBO Rate for any day shall be based on the rate appearing on the Reuters Screen LIBOR01 Page (or on any successor or substitute page of such service, or any successor to or substitute for such service, providing rate quotations comparable to those currently provided on such page of

such service, as determined by the Administrative Agent from time to time for purposes of providing quotations of interest rates applicable to dollar deposits in the London interbank market) at approximately 11:00 a.m., London time, on such day. Any change in the Alternate Base Rate due to a change in the Prime Rate, the Federal Funds Effective Rate or the Adjusted LIBO Rate shall be effective from and including the effective date of such change in the Prime Rate, the Federal Funds Effective Rate or the Adjusted LIBO Rate, respectively .

(c)         The definition of “ Applicable Margin ” in Section 1.01 of the Credit Agreement is hereby amended (i) to add the phrase “any ABR Loan or” after the phrase “with respect to” in the first sentence thereof, (ii) to add the phrase ““ABR Spread”,” after the word “caption” and before the words ““Eurodollar Spread”” in the first sentence thereof, (iii) to replace the table set forth therein with the following table:

and (iv) to delete the last sentence in the first paragraph below the table set forth therein which begins with “Applicable Margin”.

(d)         The definition of “ PV ” in Section 1.01 of the Credit Agreement is hereby amended in its entirety to read as follows:

“ PV ” means the sum of (a) the calculation of the net present value of projected future cash flows from Proved Reserves based upon the most recently delivered Reserve Information (using the arithmetical average of the discount rate and customary price deck of JPMorgan Chase Bank, N.A. and Wachovia Bank, National Association as of the effective date of such Reserve Information, giving effect to the Borrower’s hedging arrangements and long-term contracts, and using future capital and lease operating cost assumptions proposed by the Borrower and reasonably acceptable to JPMorgan Chase Bank, N.A. and Wachovia Bank, National Association), plus (b) an amount equal to 75% of the market value of the MLP Units as of the last day of the fiscal quarter ending on or prior to date of calculation, which shall not exceed the lesser of $500,000,000 or 10% of PV. For purposes of calculating the PV, a maximum of 35% of the PV value will be included from Proved Reserves that are not proved developed producing reserves. If, during any period between the effective dates of the Reserve Information, the aggregate fair market value, in the reasonable opinion of the Borrower, of Oil and Gas Properties and the MLP Units disposed of or purchased by the Borrower and the Restricted Subsidiaries shall exceed $100,000,000 in the aggregate, then the PV for such period

shall be reduced or increased, as the case may be, from time to time, by an amount equal to the value assigned such Oil and Gas Properties and the MLP Units in the most recent calculation of the PV for such period (or if no value was assigned, by an amount agreed to by the Borrower, JPMorgan Chase Bank, N.A. and Wachovia Bank, National Association). PV shall reflect the deferred revenue with respect to production payments included in Total Debt, at a value that is equal to the amount of deferred revenues so included in Total Debt.

(e)         The following definitions are hereby added in Section 1.01 the Credit Agreement where alphabetically appropriate to read as follows:

“ Defaulting Lender ” means any Lender, as reasonably determined by the Administrative Agent, that has (a) failed to fund any portion of its Loans or participations in Letters of Credit or Swingline Loans within three Business Days of the date required to be funded by it hereunder, (b) notified the Borrower, the Administrative Agent, the Issuing Bank, the Swingline Lender or any Lender in writing that it does not intend to comply with any of its funding obligations under this Agreement or has made a public statement that it does not intend to comply with its funding obligations under this Agreement, (c) otherwise failed to pay over to the Administrative Agent or any other Lender any other amount required to be paid by it hereunder within three Business Days of the date when due, unless the subject of a good faith dispute, or (d) become the subject of a bankruptcy or insolvency proceeding, or has had a receiver, conservator, trustee or custodian appointed for it, or has taken any action in furtherance of, or indicating its consent to, approval of or acquiescence in any such proceeding or appointment or has a parent company that has become the subject of a bankruptcy or insolvency proceeding, or has had a receiver, conservator, trustee or custodian appointed for it, or has taken any action in furtherance of, or indicating its consent to, approval of or acquiescence in any such proceeding or appointment; provided that the Administrative Agent shall provide written notice to any Lender determined by the Administrative Agent to be a Defaulting Lender hereunder.

“ MLP Units ” means any units in Pioneer Southwest Energy Partners L.P. owned by the Borrower or any Restricted Subsidiary.

“ Third Amendment ” means that certain Third Amendment to Credit Agreement dated as of April 29, 2009 among the Borrower, the Administrative Ag