FIFTEENTH SUPPLEMENTAL INDENTURE

Exhibit 4.13

Execution Version

FIFTEENTH SUPPLEMENTAL INDENTURE

This Fifteenth Supplemental Indenture, dated as of October 26, 2012 (this “Supplemental Indenture”), among PXP Offshore LLC, a Delaware limited liability company (the “New Subsidiary Guarantor”), Plains Exploration & Production Company, a Delaware corporation (together with its successors and assigns, the “Company”), the existing subsidiary guarantors party hereto (the “Guarantors”), and Wells Fargo Bank, N.A., a national banking association, as Trustee (the “Trustee”) under the Indenture referred to below.

W I T N E S S E T H:

WHEREAS, the Company, the Guarantors and the Trustee have heretofore executed and delivered an Indenture (as amended, supplemented, waived or otherwise modified through the date hereof, the “Indenture”), dated as of March 13, 2007, as supplemented by the following:

WHEREAS, Section 10.17 of the Indenture provides that if any Domestic Restricted Subsidiary that is not a Guarantor is or becomes obligated under any Indebtedness pursuant to a Guarantee of Indebtedness of the Company or any Guarantor (other than the Notes), and the maximum principal amount of Indebtedness of such Domestic Restricted Subsidiary under such Guarantee exceeds $10.0 million, the Company shall cause that Domestic Restricted Subsidiary to Guarantee the Notes and become a Guarantor, pursuant to the Subsidiary Guarantee provisions of the Indenture, by executing a supplemental indenture and delivering it to the Trustee within 30 days after the date on which such Domestic Restricted Subsidiary Guaranteed such Indebtedness of the Company or a Guarantor; provided, however, that the Company shall not be required to cause such Domestic Restricted Subsidiary to so Guarantee the Notes and become a Guarantor prior to the 180th day after the consummation of any transaction (including without limitation any merger, consolidation or purchase) pursuant to which such Domestic Restricted Subsidiary becomes a Subsidiary of the Company; and

WHEREAS, pursuant to Section 9.1 of the Indenture, the Trustee, the Guarantors and the Company are authorized to execute and deliver this Supplemental Indenture to amend the Indenture, without the consent of any holder of the Notes.

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, the New Subsidiary Guarantor, the Company, the Guarantors and the Trustee mutually covenant and agree for the equal and ratable benefit of the Holders of the Notes as follows:

ARTICLE I

Definitions

SECTION 1.1 Defined Terms. As used in this Supplemental Indenture, capitalized terms used, but not otherwise defined herein are used herein as defined in the Indenture. The words “herein,” “hereof” and “hereby” and other words of similar import used in this Supplemental Indenture refer to this Supplemental Indenture as a whole and not to any particular section hereof.

ARTICLE II

Agreement to be Bound

SECTION 2.1 Agreement to be Bound. The New Subsidiary Guarantor hereby becomes a party to the Indenture as a Guarantor and as such will have all of the rights and be subject to all of the obligations and agreements of a Guarantor under the Indenture. The New Subsidiary Guarantor agrees to be bound by all of the provisions of the Indenture applicable to a Guarantor and to perform all of the obligations and agreements of a Guarantor under the Indenture.

ARTICLE III

Miscellaneous

SECTION 3.1 Parties. Nothing expressed or mentioned herein is intended or shall be construed to give any Person, firm or corporation, other than the Holders and the Trustee, any legal or equitable right, remedy or claim under or in respect of this Supplemental Indenture or the Indenture or any provision herein or therein contained.

SECTION 3.2 Governing Law. This Supplemental Indenture shall be governed by, and construed in accordance with, the laws of the State of New York.

SECTION 3.3 Severability Clause. In case any provision in this Supplemental Indenture shall be invalid, illegal or unenforceable, the validity, legality and enforceability of the remaining provisions shall not in any way be affected or impaired thereby and such provision shall be ineffective only to the extent of such invalidity, illegality or unenforceability.

SECTION 3.4 Ratification of Indenture; Supplemental Indentures Part of Indenture. Except as expressly amended hereby, the Indenture is in all respects ratified and confirmed and all the terms, conditions and provisions thereof shall remain in full force and effect. This Supplemental Indenture shall form a part of the Indenture for all purposes with respect to the Notes, and every Holder of Notes heretofore or hereafter authenticated and delivered shall be bound hereby. The Trustee makes no representation or warranty as to the validity or sufficiency of this Supplemental Indenture.

SECTION 3.5 Counterparts. The parties hereto may sign one or more copies of this Supplemental Indenture in counterparts, all of which together shall constitute one and the same agreement.

SECTION 3.6 Headings. The headings of the Articles and the sections in this Supplemental Indenture are for convenience of reference only and shall not be deemed to alter or affect the meaning or interpretation of any provisions hereof.

SECTION 3.7 The Trustee. The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Supplemental Indenture or for or in respect of the recitals contained herein, all of which recitals are made solely by Company, the Guarantors, and the New Subsidiary Guarantor.

[Signature Pages Follow]

IN WITNESS WHEREOF, the parties hereto have caused this Fifteenth Supplemental Indenture to be duly executed as of the date first above written.