Exhibit
      10.6




**FIRST
      AMENDMENT TO THE**




**FIRST
      AMENDED AND RESTATED AGREEMENT OF LIMITED PARTNERSHIP OF**




**RIO
      VISTA ENERGY PARTNERS L.P.**




This
      First Amendment to the First Amended and Restated Agreement of Limited
      Partnership of Rio Vista Energy Partners L.P., dated as of October 26, 2005
      (this “First Amendment”), is entered into by and between Rio Vista GP LLC,
      a Delaware limited liability company, as the General Partner, and the Limited
      Partners of Rio Vista Energy Partners L.P., a Delaware limited partnership
      (the “Partnership”). Capitalized terms used, and not otherwise defined,
      herein shall have the same meaning as set forth in the First Amended and
      Restated Agreement of Limited Partnership of the Partnership dated as of
      September 16, 2004 (the “Partnership Agreement”).




WHEREAS,
      the General Partner and the Limited Partners are party to the Partnership
      Agreement; and




WHEREAS,
      in accordance with Section 13.2 of the Partnership Agreement, on
      August 9, 2005, the General Partner proposed an amendment to the
      Partnership Agreement on the terms set forth herein; and




WHEREAS,
      in accordance with Section 13.3(d) of the Partnership Agreement, the
      Partnership obtained an opinion of counsel dated September 20, 2005, to the
      effect that such amendment will not affect the limited liability of any Limited
      Partner under Delaware law; and




WHEREAS,
      in accordance with Section 13.2 of the Partnership Agreement, the holders
      of a Unit Majority approved such amendment at a Special Meeting of the
      Unitholders held on October 26, 2005; and




WHEREAS,
      in accordance with Section 2.6 of the Partnership Agreement, each of the
      Limited Partners has constituted and appointed the General Partner as agent
      and
      attorney-in-fact to execute any amendment to the Partnership Agreement approved
      in accordance with the terms of the Partnership Agreement.




NOW,
      THEREFORE, the General Partner and the Limited Partners agree as
      follows:




1. Amendment
      of Section 12.1 of the Partnership Agreement . Paragraph (d)
      of Section 12.1 (Dissolution) of the Partnership Agreement which currently
      reads:




“(d)
            the
                sale of all or substantially all of the assets and properties of
                the
                Partnership Group.”





is
      hereby
      amended to read as follows:





“(d)
            the
                distribution to the Partners of all or substantially all of the net
                proceeds from the sale of all or substantially all of the assets
                and
                properties of the Partnership
                Group.”





2. Effect
      of This Amendment .
      Except
      as expressly provided in this First Amendment, the Partnership Agreement is
      reaffirmed and remains in full force and effect.





3. Incorporation
      by Reference .
      The
      provisions of the Partnership Agreement, including without limitation Article
      15
      ( General
      Provisions ),
      are
      incorporated herein by reference. All references to “this Agreement” contained
      in such provisions shall be deemed to refer to the Partnership Agreement, as
      amended by this First Amendment.


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IN
      WITNESS WHEREOF, the parties have executed this First Amendment to the First
      Amended and Restated Agreement of Limited Partnership of Rio Vista Energy
      Partners L.P. as of the day and year first set forth above.


**GENERAL
                  PARTNER:**RIO
                  VISTA GP LLC,a
                  Delaware limited liability companyBy:
              /s/
                Charles C. HandlyCharles
                  C. Handly, President**LIMITED
                  PARTNERS**:By:
              Rio
                  Vista GP LLC, General Partner,as
                agent and attorney-in-factBy:
              /s/
                Charles C. HandlyCharles
                  C. Handly, President




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