EXHIBIT 10.18

                               FIFTH AMENDMENT TO
                            AGREEMENT OF PARTNERSHIP
                       GEODYNE PRODUCTION PARTNERSHIP II-C



      This Fifth  Amendment to Agreement of  Partnership  of Geodyne  Production
Partnership  II-C (the  "Partnership")  is entered  into by and between  Geodyne
Resources,  Inc.  ("Resources"),  a Delaware corporation,  as successor Managing
Partner, and Geodyne Energy Income Limited Partnership II-C ("Geodyne II-C"), as
General Partner.

      WHEREAS,  on January 13, 1988, Geodyne Production Company  ("Production"),
as Managing Partner, and Geodyne II-C, as General Partner,  executed and entered
into that certain Agreement of Partnership of PaineWebber/Geodyne  Energy Income
Production Partnership II-C (the "Agreement"); and

      WHEREAS,  on February 26, 1993,  Production  and Geodyne II-C executed and
entered into that certain First  Amendment to Agreement,  whereby it changed (i)
the name of the Partnership from  "PW/Geodyne  Production  Partnership  II-C" to
"Geodyne  Production  Partnership  II-C",  (ii) the address of the Partnership's
principal place of business,  and (iii) the address for the Partnership's  agent
for service of process; and

      WHEREAS,   Production   merged  with  and  into   Resources,   its  parent
corporation, effective June 30, 1996; and

      WHEREAS, on July 1, 1996, Production,  Resources and Geodyne II-C executed
and  entered  into that  certain  Second  Amendment  to  Agreement,  whereby all
references to Production as Managing  Partner were amended to reflect,  instead,
Resources as Managing Partner; and

      WHEREAS,  on November 14, 2001,  Resources  executed and entered into that
certain Third  Amendment to Agreement  whereby the term of the  partnership  was
extended for an additional two years, until December 31, 2003; and

      WHEREAS,  on November 18, 2003,  Resources  executed and entered into that
certain Fourth  Amendment to Agreement  whereby the term of the  partnership was
extended for an additional two years, until December 31, 2005; and

      WHEREAS,  Section 10.1 of the Agreement provides that the managing partner
of the partnership (the "Managing Partner") may, without prior notice or consent
of any other Partner (as defined in the Agreement),  amend any provision of this
Agreement if, in its opinion,  such amendment  does not have a material  adverse
effect upon the Limited Partnership (as defined in the Agreement); and

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      WHEREAS,  Section 2.3 of the Agreement provides that the Partnership shall
continue in full force and effect until  December 31,  2005,  provided  that the
Managing  Partner may extend the term of the Partnership for up to three periods
of two years each or until  dissolution prior thereto pursuant to the provisions
of the Agreement; and

      WHEREAS,  Resources has elected to extend the life of the  Partnership  an
additional two years.

      NOW,  THEREFORE,  be it resolved  that  Section 2.3 is hereby  amended and
rested as follows:

            The Production  Partnership shall continue in force and effect until
      December 31, 2007, provided that the Managing Partner may extend such term
      for up to two  periods  of two  years  each,  or until  dissolution  prior
      thereto pursuant to the provisions thereof.

       IN WITNESS  WHEREOF,  the parties hereto have hereunto set their hands as
of the 27th day of October, 2005.

                                       Geodyne Resources, Inc.
                                       as Managing Partner

                                       By: //s// Dennis R. Neill
                                            ----------------------------
                                            Dennis R. Neill
                                            President

                                       Geodyne Energy Income Limited
                                       Partnership II-C
                                       as General Partner

                                       By Geodyne Resources, Inc.
                                          General Partner

                                       By: //s// Dennis R. Neill
                                            ----------------------------
                                            Dennis R. Neill
                                            President


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