EXHIBIT 4.31

                               Sixth Amendment to
               Agreement and Certificate of Limited Partnership of
                 Geodyne Energy Income Limited Partnership II-C


      This Sixth Amendment to Agreement and  Certificate of Limited  Partnership
of Geodyne Energy Income Limited Partnership II-C (the "Partnership") is entered
into  by  and  between  Geodyne  Resources,   Inc.  ("Resources"),   a  Delaware
corporation,   as  successor  General  Partner,   Geodyne   Depositary   Company
("Depositary"),  a  Delaware  corporation,  as  the  Limited  Partner,  and  all
Substituted Limited Partners admitted to the Partnership.

      WHEREAS, on January 13, 1988, Geodyne Properties, Inc. ("Properties"),  as
General partner, and Depositary executed and entered into that certain Agreement
and Certificate of Limited Partnership of the Partnership (the "Agreement"); and

      WHEREAS,  on February 25, 1993,  Properties executed and entered into that
certain  First  Amendment  to  Agreement  whereby it changed (i) the name of the
Partnership from "PaineWebber/Geodyne Energy Income Limited Partnership II-C" to
"Geodyne  Energy  Income  Limited  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,  on August 4th, 1993,  Properties  executed and entered into that
certain Second Amendment to the Agreement whereby it amended certain  provisions
to (i) expedite the method of accepting  transfers of Unit  Holders' (as defined
in the  Agreement)  Units in the  Partnership  and (ii)  provide for an optional
right of repurchase/redemption which may be exercised by the Unit Holders; and

      WHEREAS,   Properties  merged  with  and  into  Geodyne  Resources,   Inc.
("Resources"), its parent corporation, effective June 30, 1996; and

      WHEREAS,  on  July  1,  1996,  Resources,   as  successor  via  merger  to
Properties,  executed and entered into, as General  Partner,  that certain Third
Amendment  to the  Agreement  whereby it amended the  Agreement  to provide that
Resources,  as successor  via merger to Geodyne,  is the General  Partner of the
Partnership; and

      WHEREAS,  on November 14, 2001,  Resources  executed and entered into that
certain Fourth  Amendment to the 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 Fifth Amendment to the Agreement whereby the term of the partnership was
extended for an additional two years, until December 31, 2005; and

                                      -1-
<PAGE>



      WHEREAS,  Section 2.3 of the Agreement provides that the Partnership shall
continue in full force and effect until  December 31,  2003,  provided  that the
General  Partner may extend the term of the  Partnership for up to three periods
of two years each if it believes each such extension is in the best interests of
the Unit Holders or until  dissolution  prior thereto pursuant to the provisions
of the Agreement, and

      WHEREAS,  Section 11.1 of the Agreement  provides that the general partner
of the partnership (the "General  Partner") may, without prior notice or consent
of any Unit Holder (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 Unit Holders; and

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

      NOW,  THEREFORE,  in  consideration  of  the  covenants,   conditions  and
agreements herein contained, the parties hereto hereby agree as follows:

      Section 2.3. is hereby amended and restated as follows:

                  The  Partnership  shall  continue  in force and  effect  until
            December 31, 2005,  provided that the General Partner may extend the
            term of the  Partnership  for up to two periods of two years each if
            it believes  such  extension  is in the best  interests  of the Unit
            Holders,   or  until  dissolution  prior  thereto  pursuant  to  the
            provisions hereof.

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

                                    GEODYNE RESOURCES, INC.,
                                    as General Partner

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

                                    GEODYNE DEPOSITARY COMPANY,
                                    as the Limited Partner

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

                                    GEODYNE RESOURCES, INC.
                                    as Attorney-in-Fact for all
                                    Substituted Limited Partners

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

                                      -2-