EXHIBIT 10.21

                               SIXTH AMENDMENT TO
                              AMENDED AND RESTATED
                            AGREEMENT OF PARTNERSHIP
                        GEODYNE ENERGY INCOME PRODUCTION
                                 PARTNERSHIP I-F


      This Sixth  Amendment to Amended and Restated  Agreement of Partnership of
Geodyne Energy Income Production  Partnership I-F (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 I-F ("Geodyne I-F"), as General Partner.

      WHEREAS, on September 10, 1986, Geodyne Production Company ("Production"),
as Managing Partner,  and Geodyne I-F, as General Partner,  executed and entered
into that certain Agreement of Partnership of PaineWebber/Geodyne  Energy Income
Production Partnership I-F (the "Preformation Agreement"); and

      WHEREAS,  on December  17, 1986,  Production  and Geodyne I-F executed and
entered into that certain  Amended and Restated  Agreement of  Partnership  (the
"Agreement"); and

      WHEREAS, on February 26, 1993, but effective March 1, 1993, Production and
Geodyne I-F executed and entered  into that certain  First  Amendment to Amended
and Restated Agreement of Partnership (the "Agreement"),  whereby it changed (i)
the name of the Partnership from  "PaineWebber/Geodyne  Energy Income Production
Partnership I-F" to "Geodyne Energy Income Production Partnership I-F", (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 July 1, 1996,  Production and Geodyne I-F executed and entered
into that certain Second  Amendment to Agreement,  whereby all references in the
Agreement  to Geodyne  Production  Company as Managing  Partner  were amended to
reflect, instead, Geodyne Resources, Inc. ("Resources") as Managing Partner; and

      WHEREAS,  on November 14, 2001,  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, 2003; and

      WHEREAS,  on November 18, 2003,  Resources  executed and entered into that
certain Fifth  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
(as defined in the Agreement) 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

                                      -1-
<PAGE>



     WHEREAS,  Section 2.4 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 two 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 2.4. is hereby amended and
restated 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 one  period  of two  years,  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 Managing Partner

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

                                       Geodyne Energy Income Limited
                                       Partnership I-F
                                       as General Partner

                                       By Geodyne Resources, Inc.
                                          General Partner

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



                                      -2-