EXHIBIT 10.15

                             SUPPLEMENTAL INDENTURE

                           DATED AS OF MARCH 31, 1997

                                      AMONG

                          GERRITY OIL & GAS CORPORATION

                          PATINA OIL & GAS CORPORATION

                                       AND

                            THE CHASE MANHATTAN BANK
                       (FORMERLY KNOWN AS CHEMICAL BANK),

                                   AS TRUSTEE

                   11 3/4% SENIOR SUBORDINATED NOTES DUE 2004

                                        1

        This Supplemental  Indenture dated as of March 31, 1997 is among Gerrity
Oil & Gas Corporation, a Delaware corporation (the "Company"),  Patina Oil & Gas
Corporation,  a Delaware  corporation  ("Patina"),  and The Chase Manhattan Bank
(formerly  known as Chemical  Bank),  as Trustee,  and  supplements,  amends and
modifies  that certain  Indenture  dated as of June 30, 1994 between the Company
and the Trustee (the "Indenture"):

                                    RECITALS:

        WHEREAS, The Company is a wholly owned subsidiary of Patina;

        WHEREAS,  the Company  will merge with and into  Patina  (the  "Merger")
pursuant to a Certificate of Ownership and Merger to be filed with the Secretary
of State of the State of Delaware;

        WHEREAS,  As a result  of the  Merger,  Patina  will be the  corporation
surviving the Merger,  and the outstanding  capital stock of the Company will be
converted into capital stock of Patina;

        WHEREAS,  the Merger  will be  effected  pursuant  to Section 253 of the
General  Corporation  Law of the  State  of  Delaware  ("DGCL"),  which  permits
effectuation  of  such  a  merger  without  a vote  of  stockholders  of  either
constituent  corporation and without any action by the Board of Directors of the
Company;

        WHEREAS,  Patina and the Company  intend that  Patina  shall  assume the
obligations of the Company with respect to the Indenture;

        WHEREAS,  the Merger complies with Section 5.01 of the Indenture because
Patina  (the  Person  into which the  Company is to be merged) is a  corporation
organized  and validly  existing  under the laws of the State of  Delaware,  and
because Patina,  by its execution and delivery hereof,  expressly assumes all of
the obligations of the Company on all of the Securities and under the Indenture;

        WHEREAS,  the  Company  has  delivered  to  the  Trustee  the  Officer's
Certificate  required by Clause (v) of Section 5.01 of the Indenture,  including
the arithmetic computations demonstrating compliance with clauses (iii) and (iv)
of Section 5.01;

      WHEREAS, the Company has delivered  to the Trustee the Opinion of Counsel
required by Clause (v) of Section 5.01 of the Indenture;

      WHEREAS, this Supplemental Indenture is executed and delivered pursuant to
Section 9.01(2) of the Indenture;

        NOW, THEREFORE,  in consideration of the premises,  the covenants herein
contained and other good and valuable consideration, the receipt and sufficiency
of which are hereby  acknowledged  by the parties  hereto,  the  parties  hereto
covenant and agree as follows:

                                        1

                                    ARTICLE I

        Section 1.1 Definitions.  Capitalized  terms used but not defined herein
are defined in the Indenture  and are used herein with the meanings  ascribed to
them therein.

        Section 1.2 Assumption of the Company's Obligations under the Indenture.
Patina shall,  effective as of the  effective  time of the Merger under the DGCL
(the "Effective  Time"),  assume,  and shall thereafter  timely pay, perform and
discharge,  each and every  obligation  of the Company under and with respect to
the Securities and the Indenture.

        Section 1.3 No Default.  Immediately  after giving effect to the Merger,
no Event of Default,  and no event that, after notice or lapse of time, or both,
would become an Event of Default, has happened or is continuing.

                                   ARTICLE II

        Section 2.1  Effectiveness.Although  this Supplemental  Indenture may be
executed and  delivered  by the parties  hereto prior  thereto,  the  provisions
hereof shall not become effective unless and until the Merger becomes  effective
under  the  DGCL  and,  under  such   circumstances,   shall  become   effective
concurrently  with  the  Effective  Time of such  Merger.  From  and  after  the
Effective  Time, the Indenture,  as hereby  supplemented,  amended and modified,
shall remain in full force and effect.

        Section  2.2  References.  Each  reference  in  the  Indenture  or  this
Supplemental  Indenture  to any  article,  section,  term  or  provision  of the
Indenture  shall mean and be deemed to refer to such article,  section,  term or
provision of the Indenture, as modified by this Supplemental  Indenture,  except
where the context otherwise indicates.

        Section 2.3 Benefit.  All the covenants,  provisions,  stipulations  and
agreements  contained in this  Supplemental  Indenture  are and shall be for the
sole and exclusive benefit of the parties hereto,  their successors and assigns,
and of the holders and registered owners from time to time of the Securities, as
hereby amended and supplemented.

        Section 2.4 Counterparts. This Supplemental Indenture may be executed in
any number of counterparts, each of which shall be deemed an original and all of
which taken together shall be deemed to be a single instrument.

        Section 2.5 Governing Law. This  Supplemental  Indenture shall be deemed
to be a contract  under the laws of the State of New York,  and for all purposes
shall be construed in accordance  with the laws of such state without  regard to
principles of conflicts of laws,  except as may otherwise  required by mandatory
provisions of law.

                                        2

         Section 2.6  Headings.  The Article and Section headings herein are for
convenience only and shall not affect the construction hereof.

        Section 2.7 Recitals.  The recitals  contained  herein shall be taken as
statements  of  Patina,  and the  Trustee  assumes no  responsibility  for their
correctness.  The  Trustee  makes  no  representations  as to  the  validity  or
sufficiency of this Supplemental Indenture.

        IN WITNESS WHEREOF, the said Gerrity Oil & Gas Corporation, Patina Oil &
Gas Corporation and The Chase Manhattan Bank have each caused this  Supplemental
Indenture  to be executed  in its  corporate  name by the officer  whose name is
subscribed below, all as of the day and year first above written.

                                      GERRITY OIL & GAS CORPORATION

                                      By:      /S/ BRIAN J. CREE
                                      Name:        Brian J. Cree,
                                      Title:       Executive Vice President
                                                 and  Chief Operating Officer

                                      PATINA OIL & GAS CORPORATION

                                      By:      /S/ DAVID J. KORNDER
                                      Name:        David J. Kornder,
                                      Title:       Vice President

                                      THE CHASE MANHATTAN BANK, as Trustee

                                      By:      /S/ WANDA EILAND
                                      Name:    Wanda Eiland,
                                     Title:

                                        3