Exhibit 4.A


    Exhibit
      4.A

    


    Execution
      Copy

    


     

      
        

      

    

     

    FOURTH
      SUPPLEMENTAL INDENTURE

     

    among

     

    EL
      PASO EXPLORATION & PRODUCTION COMPANY,

     

    as
      Issuer,

     

    EL
      PASO PRODUCTION COMPANY,

     

    MEDICINE
      BOW ENERGY CORPORATION,

     

    MEDICINE
      BOW OPERATING COMPANY,

     

    MBOW
      FOUR STAR CORPORATION,

     

    EL
      PASO PRODUCTION OIL & GAS COMPANY,

     

    EL
      PASO E&P HOLDINGS, INC.,

     

    EL
      PASO E&P COMPANY, L.P.,

     

    EL
      PASO PRODUCTION RESALE COMPANY,

     

    EL
      PASO ENERGY OIL TRANSMISSION, L.L.C.

     

    and

     

    EL
      PASO PRODUCTION OIL & GAS GATHERING, L.P.,

     

    as
      Subsidiary Guarantors,

     

    and

     

    WILMINGTON
      TRUST COMPANY

     

    as
      Trustee

     

    ______________

     

    December
      31, 2005

     

    ______________

     

     

    73⁄4%
      Senior Notes due 2013

     

    


     

      
        

      

    

    



    FOURTH
      SUPPLEMENTAL INDENTURE

     

    


    This
      Fourth Supplemental Indenture, dated as of December 31, 2005 (this “Fourth
      Supplemental Indenture”),
      is entered into by and among (i) El Paso Exploration & Production Company
      (the “Company”),
      formerly known as El Paso Production Holding Company, (ii) El Paso Production
      Company, Medicine Bow Energy Corporation, Medicine Bow Operating Company, MBOW
      Four Star Corporation, El Paso Production Oil & Gas Company, El Paso E&P
      Holdings, Inc., El Paso E&P Company, L.P., El Paso Production Resale
      Company, El Paso Energy Oil Transmission, L.L.C. and El Paso Production Oil
      & Gas Gathering, L.P. (collectively, the “Subsidiary
      Guarantors”),
      and (iii) Wilmington Trust Company, as trustee (the “Trustee”).
      Capitalized terms used but not defined herein have the meanings ascribed to
      them
      in the Original Indenture (as defined below).

     

    W
      I T N E S S E T H:

     

    WHEREAS,
      the Company, El Paso Production Company (“El
      Paso Production”),
      El Paso Production GOM Inc. (“GOM”),
      Vermejo Minerals Corporation (“Vermejo”)
      and El Paso Energy Raton, L.L.C. (“Raton”)
      have heretofore executed and delivered to the Trustee that certain Indenture,
      dated as of May 23, 2003 (the “Original
      Indenture”),
      providing for the issuance of $1,200,000,000 aggregate principal amount of
      the
      Company’s 73⁄4% Senior Notes due 2013 (the “Notes”);

     

    WHEREAS,
      as set forth in the First Supplemental Indenture (as defined below), Raton
      and
      Vermejo entered into an Agreement of Merger, pursuant to which (i) Raton was
      merged with and into Vermejo, (ii) Vermejo was the surviving corporation of
      the
      merger contemplated by such agreement, and (iii) Vermejo’s name was changed to
“El Paso Energy Raton Corporation” (“Raton
      Corporation”);

     

    WHEREAS,
      the Company, El Paso Production, GOM, Vermejo and the Trustee entered into
      that
      certain First Supplemental Indenture, dated as of January 31, 2004 (the
“First
      Supplemental Indenture”),
      pursuant to which the Original Indenture was amended and Vermejo expressly
      assumed the obligations of Raton under its Subsidiary Guarantee;

     

    WHEREAS,
      the Company, El Paso Production, GOM, Raton Corporation and the Trustee entered
      into that certain Second Supplemental Indenture, dated as of July 26, 2004
      (the “Second
      Supplemental Indenture”),
      pursuant to which the Original Indenture (as supplemented by the First
      Supplemental Indenture) was further amended and certain covenants were added
      for
      the benefit of the Holders pursuant to Section 9.01(6) of the Original
      Indenture;

     

    WHEREAS,
      the Company, El Paso Production, GOM, Raton Corporation, Medicine Bow Energy
      Corporation (“Medicine
      Bow”),
      Medicine Bow Operating Company (“MBOW
      Operating”)
      and MBOW Four Star Corporation (“MBOW
      Four Star”)
      entered into that certain Third Supplemental Indenture, dated as of August
      31,
      2005 (the “Third
      Supplemental Indenture”),
      pursuant to which the Original Indenture (as supplemented by the First
      Supplemental Indenture and the Second Supplemental Indenture) was further
      amended and Medicine Bow, MBOW Operating and MBOW Four Star each expressly
      assumed the obligations of a Subsidiary Guarantor under the Original Indenture
      (as supplemented by the First Supplemental Indenture and the Second Supplemental
      Indenture);

     

    WHEREAS,
      as of the date hereof, pursuant to the reorganization of certain subsidiaries
      of
      El Paso Corporation (the “Reorganization”),
      (a) El Paso Production Oil & Gas Company, a Delaware corporation
      (“El
      Paso POG”),
      El Paso E&P Holdings, Inc., a Delaware corporation formerly known as El Paso
      Production Oil & Gas Holdings, Inc. (“El
      Paso Holdings”),
      El Paso E&P Company, L.P., a Delaware limited partnership formerly known as
      El Paso Production Oil & Gas USA, L.P. (“El
      Paso E&P”),
      El Paso Production Resale Company, a Delaware corporation (“El
      Paso Resale”),
      El Paso Energy Oil Transmission, L.L.C., a Delaware limited liability company
      (“El
      Paso Transmission”)
      and El Paso Production Oil & Gas Gathering, L.P., a Delaware limited
      partnership (“El
      Paso Gathering”),
      became direct or indirect wholly owned subsidiaries of the Company and (b)
      El
      Paso Production Holding Company changed its name to El Paso Exploration &
Production Company;

     

    WHEREAS,
      the Company and the Subsidiary Guarantors now desire to further amend the
      Original Indenture (as supplemented by the First Supplemental Indenture, the
      Second Supplemental Indenture and the Third Supplemental Indenture, and as
      so
      supplemented, the “Indenture”)
      to include El Paso POG, El Paso Holdings, El Paso E&P, El Paso Resale, El
      Paso Transmission and El Paso Gathering as parties to the Indenture as
      guarantors of the Company’s obligations under the Notes, subject to the terms
      and conditions of the Indenture and the Notes;

     

    WHEREAS,
      pursuant to the Reorganization, GOM, Raton Corporation and El Paso E&P
      entered into and consummated an Agreement of Merger, as of the date hereof,
      pursuant to which (a) GOM and Raton Corporation merged with and into El Paso
      E&P and (b) El Paso E&P is the surviving entity of the
      merger;

     

    WHEREAS,
      Section 5.01(b) of the Original Indenture provides that, in connection with
      a
      merger of any Subsidiary Guarantor with or into any Person, such Person shall
      expressly assume the obligations of such Subsidiary Guarantor under its
      Subsidiary Guarantee;

     

    WHEREAS,
      El Paso E&P desires to expressly assume the obligations of GOM and Raton
      Corporation under their respective Subsidiary Guarantees; and

     

    WHEREAS,
      the Trustee, upon satisfaction of all actions and conditions on the part of
      the
      Company and the Subsidiary Guarantors necessary for the execution, delivery
      and
      performance of this Fourth Supplemental Indenture (including, without
      limitation, the receipt of an Officers’ Certificate and an Opinion of Counsel)
      is willing to amend the Indenture as hereinafter set forth;

     

    NOW,
      THEREFORE, the Company, the Subsidiary Guarantors and the Trustee mutually
      covenant and agree for the equal and proportionate benefit of all Holders of
      the
      Notes as follows:

     

    ARTICLE
      1

     

    Section
      1.01 This
      Fourth Supplemental Indenture is supplemental to the Original Indenture, as
      previously amended by the First Supplemental Indenture, the Second Supplemental
      Indenture and the Third Supplemental Indenture, and does and shall be deemed
      to
      form a part of, and shall be construed in connection with and as a part of,
      the
      Original Indenture, as so amended and supplemented, for any and all
      purposes.

     

    Section
      1.02 This
      Fourth Supplemental Indenture shall become effective immediately upon its
      execution and delivery by each of the Company, the Subsidiary Guarantors and
      the
      Trustee.

     

    ARTICLE
      2

     

    Section
      2.01 The
      Company, the Subsidiary Guarantors and the Trustee hereby acknowledge and agree
      that each of El Paso POG, El Paso Holdings, El Paso E&P, El Paso Resale, El
      Paso Transmission and El Paso Gathering (collectively, the “New
      Subsidiary Guarantors”)
      hereby becomes a party to the Indenture, as a Subsidiary Guarantor, and as
      such
      will have all of the rights and be subject to all of the obligations and
      agreements of a Subsidiary Guarantor under the Indenture. The New Subsidiary
      Guarantors agree to be bound by all of the provisions of the Indenture
      applicable to a Subsidiary Guarantor and to perform all of the obligations
      and
      agreements of a Subsidiary Guarantor under the Indenture. Each New Subsidiary
      Guarantor hereby provides a full, unconditional and irrevocable Guarantee,
      as
      primary obligor and not merely as surety, jointly and severally with each other
      Subsidiary Guarantor, to each Holder and to the Trustee and their successors
      and
      assigns, on the terms and subject to the conditions set forth in the Indenture,
      including but not limited to Article 10 thereof.

     

    ARTICLE
      3

     

    Section
      3.01 El
      Paso E&P hereby assumes all of the obligations of GOM and Raton Corporation
      under the Original Indenture, including all their obligations under their
      respective Subsidiary Guarantees.

     

    ARTICLE
      4

    


    Section
      4.01 Except
      as specifically modified herein, the Notes and the Indenture are in all respects
      ratified and confirmed and shall remain in full force and effect in accordance
      with their terms. This Fourth Supplemental Indenture shall form a part of the
      Indenture for all purposes, and every Holder of Notes heretofore or hereafter
      authenticated and delivered shall be bound hereby. The Trustee shall not be
      responsible in any manner whatsoever for or in respect of the validity or
      sufficiency of this Fourth Supplemental Indenture or for or in respect of the
      recitals contained herein, all of which are made solely by the Company and
      the
      Subsidiary Guarantors.

     

    Section
      4.02 Except
      as otherwise expressly provided herein, no duties, responsibilities or
      liabilities are assumed, or shall be construed to be assumed, by the Trustee
      by
      reason of this Fourth Supplemental Indenture. This Fourth Supplemental Indenture
      is executed and accepted by the Trustee subject to all the terms and conditions
      set forth in the Indenture with the same force and effect as if those terms
      and
      conditions were repeated at length herein and made applicable to the Trustee
      with respect hereto. In entering into this Fourth Supplemental Indenture, the
      Trustee shall be entitled to the benefit of every provision of the Indenture
      relating to the conduct or affecting the liability or affording protection
      to
      the Trustee, regardless of whether elsewhere herein so provided, including
      indemnification pursuant to Section 7.07 of the Original Indenture, and the
      Company acknowledges that the Trustee shall be entitled to indemnification
      pursuant to Section 7.07 of the Original Indenture against any and all loss,
      liability or expense (including attorney’s fees) in connection with the
      Trustee’s signing this Fourth Supplemental Indenture.

     

    Section
      4.03 THIS
      FOURTH SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE
      WITH, THE LAWS OF THE STATE OF NEW YORK.

     

    Section
      4.04 This
      Fourth Supplemental Indenture may be executed in any number of counterparts,
      each of which when so executed and delivered shall be deemed an original, but
      all such counterparts together shall constitute but one and the same
      instrument.

     

    Section
      4.05 All
      notices and other communications to the New Subsidiary Guarantors shall be
      given
      as provided in Section 11.02 of the Original Indenture for notices to Subsidiary
      Guarantors.

     

    [Signature
      page follows.]

     


    
      
         

        
        

      

      
        
        

        
          

        

      

      
        
        

      

    


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

     

     

    Issuer:

     

    EL
      PASO EXPLORATION & PRODUCTION COMPANY

     

    By:    
      /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Chief Financial Officer, Controller and Treasurer

     

     

    Subsidiary
      Guarantors:

     

    EL
      PASO PRODUCTION COMPANY

     

    By:   
       /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Controller and Treasurer


     

     

    MEDICINE
      BOW ENERGY CORPORATION

     

    By:    
      /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Controller and Treasurer

     

     

    MEDICINE
      BOW OPERATING COMPANY

     

    By:    
      /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Controller and Treasurer

     

     

    MBOW
      FOUR STAR CORPORATION

     

    By:   
      /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Controller and Treasurer

     

     

    EL
      PASO PRODUCTION OIL & GAS COMPANY

     

    By:    
      /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Controller and Treasurer

     

     

    EL
      PASO E&P HOLDINGS, INC.

     

    By:    
      /s/ Andrew T.
      Ponocciome                


        Andrew
      T.
      Ponocciome

    
          President

       

    

     

    EL
      PASO E&P COMPANY, L.P.

     

    By:    
      /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Controller and Treasurer

     

     

    EL
      PASO PRODUCTION RESALE COMPANY

     

    By:    
      /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Controller and Treasurer

     

     

    EL
      PASO ENERGY OIL TRANSMISSION, L.L.C.

     

    By:    
      /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Controller and Treasurer

     

     

    EL
      PASO PRODUCTION OIL & GAS GATHERING, L.P.

     

    By:    
      /s/ Gene T.
      Waguespack                   


        Gene
      T.
      Waguespack

        Senior
      Vice
      President, Controller and Treasurer

     

     

     

    Trustee:

     

     

    WILMINGTON
      TRUST COMPANY, as Trustee

     

     

    By:    /s/
      Suzanne J. Mac
      Donald             

    Name:   
      Suzanne J. Mac Donald

    Title:      
      Vice President