<PAGE>   1

                                                                    EXHIBIT 10.5
                               FIRST AMENDMENT TO
                  SUPPLEMENTAL EXECUTIVE RETIREMENT AGREEMENT


         This First Amendment (the "Amendment") to Supplemental Executive
Retirement Agreement (the "Agreement") is made and entered into at Englewood in
Colorado on the 26th day of October, 1995, by and between PRESIDIO OIL COMPANY
(the "Company") and GEORGE P. GIARD, JR. (the "Executive").

         WHEREAS, the Board of Directors of the Company has authorized the
Company to negotiate an Asset Acquisition (as defined below) or a
Recapitalization (as defined below) of the Company with certain of the holders
of its securities which may result in a Change of Control (as defined below);
and

         WHEREAS, the Board of Directors of the Company has determined that,
pending the consummation of any such transactions, it is imperative that the
Company be able to rely upon the Executive to continue in the Executive's
position and that the Company be able to receive and rely upon the Executive's
advice, if requested, as to the best interest of the Company, and its
shareholders without concern that the Executive might be distracted by the
personal uncertainties and risk created by the proposed transactions.

         NOW, THEREFORE, to assure the Company that it will have the continued
dedication of the Executive and the availability of the Executive's advice and
counsel notwithstanding the anticipated consummation of the foregoing
transactions and to induce the Executive to remain in the employ of the
Company, and for other good and valuable consideration, the Company and the
Executive agree as follows:

         1.      Section 2.5 of the Agreement is deleted in its entirety and
                 replaced by the following:

                 "2.5     TERMINATION PRIOR TO RETIREMENT.


                          (a)     Upon the Executive's Termination of
                 employment with the Company (other than Termination for Cause
                 or a Termination specified in paragraph (b) below) prior to
                 Normal Retirement or Early Retirement and when the Executive
                 is Vested, he will receive benefits in accordance with
                 Sections 2.1, 2.3 and 2.4 of this Agreement (using his
                 Retirement Percentage and Final Average Earnings as of the
                 date of Termination of employment), commencing on the last day
                 of the calendar month following the month in which the
                 Executive attains age 65.

                          (b)     Upon the Executive's Termination of
                 employment with the





                                      -1-
<PAGE>   2
                 Company (other than a Termination for Cause) (i) prior to
                 Normal Retirement or Early Retirement, (ii) when the Executive
                 is Vested and (iii) within two (2) years following the
                 Recapitalization, an Asset Acquisition or a Change in Control
                 (or, if prior to the Recapitalization, an Asset Acquisition or
                 a Change in Control, the Executive's Termination of employment
                 is reasonably demonstrated by the Executive to be at the
                 request of a third party who has taken steps reasonably
                 calculated to effect the Recapitalization, an Asset
                 Acquisition or a Change of Control or otherwise arose in
                 connection with or anticipation of the Recapitalization, an
                 Asset Acquisition or a Change in Control), he will have the
                 option by delivery of written notice to the Company no later
                 than three (3) days following his Termination of employment to
                 receive benefits as set forth in paragraph (a) above or in a
                 lump sum payment payable not later than five (5) days
                 following his Termination of employment in an amount equal to
                 the Present Value of the benefits he is otherwise entitled to
                 receive in accordance with paragraph (a) above."

         2.      Article VI of the Agreement is amended by adding the following
                 definitions thereto:

                 An "Asset Acquisition" shall be deemed to have occurred if any
                 Person, a group or groups of related or unrelated Persons
                 acquires more than fifty-one percent (51%) in value of the oil
                 and gas properties of the Company pursuant to one or more
                 transactions with the Company during the term of this
                 Agreement.

                 "Beneficial Owner" shall have the meaning set forth in Rules
                 13d-3 and 13d-5 under the Securities Exchange Act of 1934, as
                 in effect on May 1, 1995.

                 A "Change in Control" shall be deemed to have occurred if (i)
                 any Person is or becomes the Beneficial Owner of securities of
                 the Company representing thirty percent (30%) or more of the
                 Voting Power, (ii) there shall occur a change in the
                 composition of a majority of the Board within any period of
                 four (4) consecutive years which change shall not have been
                 approved by a majority of the Board as constituted immediately
                 prior to such change in composition, (iii) at any meeting of
                 the shareholders of the Company called for the purpose of
                 electing directors, more than one of the persons nominated by
                 the Board for election as directors shall fail to be elected,
                 or (iv) the consummation of a merger, consolidation, sale of
                 substantially all assets or other reorganization of the
                 Company, other than a reincorporation, in which the Company
                 does not survive.

                 "Person" shall have the meaning set forth in Sections 3(a)(9)
                 and 13(d)(3) of the Securities Exchange Act of 1934, as in
                 effect on May 1, 1995.





                                      -2-
<PAGE>   3
                 "Present Value" shall be calculated by utilizing a discount
                 factor equal to the prime rate published by The Chase
                 Manhattan Bank, N.A. as of the date of Termination of
                 employment.

                 The "Recapitalization" shall be deemed to have occurred if the
                 capital structure of the Company is changed in respect of the
                 holders of its debt securities which may involve a Change of
                 Control.

                 "Voting Power" shall mean the voting power of the outstanding
                 securities of the Company having the right under ordinary
                 circumstances to vote at an election of the Board.

         3.      Except as expressly amended hereby, the Agreement shall remain
                 in full force and effect in accordance with its terms.

         IN WITNESS WHEREOF, the Company and the Executive have executed this
Amendment on the date first written above.

                                        PRESIDIO OIL COMPANY





                                        By: /s/ Judson Williams           
                                            -------------------------------
                                            Judson Williams, Treasurer

                                        EXECUTIVE
                                                                     




                                        By: /s/ George P. Giard, Jr.     
                                            ------------------------------
                                            George P. Giard, Jr.





                                      -3-
<PAGE>   4

                               FIRST AMENDMENT TO
                  SUPPLEMENTAL EXECUTIVE RETIREMENT AGREEMENT


         This First Amendment (the "Amendment") to Supplemental Executive
Retirement Agreement (the "Agreement") is made and entered into at Englewood in
Colorado on the 26th day of October, 1995, by and between PRESIDIO OIL COMPANY
(the "Company") and ROBERT L. SMITH (the "Executive").

        WHEREAS, the Board of Directors of the Company has authorized the
Company to negotiate an Asset Acquisition (as defined below) or a
Recapitalization (as defined below) of the Company with certain of the holders
of its securities which may result in a Change of Control (as defined below);
and

         WHEREAS, the Board of Directors of the Company has determined that,
pending the consummation of any such transactions, it is imperative that the
Company be able to rely upon the Executive to continue in the Executive's
position and that the Company be able to receive and rely upon the Executive's
advice, if requested, as to the best interest of the Company, and its
shareholders without concern that the Executive might be distracted by the
personal uncertainties and risk created by the proposed transactions.

         NOW, THEREFORE, to assure the Company that it will have the continued
dedication of the Executive and the availability of the Executive's advice and
counsel notwithstanding the anticipated consummation of the foregoing
transactions and to induce the Executive to remain in the employ of the
Company, and for other good and valuable consideration, the Company and the
Executive agree as follows:

         1.      Section 2.5 of the Agreement is deleted in its entirety and
                 replaced by the following:

                 "2.5     TERMINATION PRIOR TO RETIREMENT.


                          (a)     Upon the Executive's Termination of
                 employment with the Company (other than Termination for Cause
                 or a Termination specified in paragraph (b) below) prior to
                 Normal Retirement or Early Retirement and when the Executive
                 is Vested, he will receive benefits in accordance with
                 Sections 2.1, 2.3 and 2.4 of this Agreement (using his
                 Retirement Percentage and Final Average Earnings as of the
                 date of Termination of employment), commencing on the last day
                 of the calendar month following the month in which the
                 Executive attains age 65.

                          (b)     Upon the Executive's Termination of
                  employment with the





                                      -1-



<PAGE>   5
                 Company (other than a Termination for Cause) (i) prior to
                 Normal Retirement or Early Retirement, (ii) when the Executive
                 is Vested and (iii) within two (2) years following the
                 Recapitalization, an Asset Acquisition or a Change in Control
                 (or, if prior to the Recapitalization, an Asset Acquisition or
                 a Change in Control, the Executive's Termination of employment
                 is reasonably demonstrated by the Executive to be at the
                 request of a third party who has taken steps reasonably
                 calculated to effect the Recapitalization, an Asset
                 Acquisition or a Change of Control or otherwise arose in
                 connection with or anticipation of the Recapitalization, an
                 Asset Acquisition or a Change in Control), he will have the
                 option by delivery of written notice to the Company no later
                 than three (3) days following his Termination of employment to
                 receive benefits as set forth in paragraph (a) above or in a
                 lump sum payment payable not later than five (5) days
                 following his Termination of employment in an amount equal to
                 the Present Value of the benefits he is otherwise entitled to
                 receive in accordance with paragraph (a) above."

         2.      Article VI of the Agreement is amended by adding the following
                 definitions thereto:

                 An "Asset Acquisition" shall be deemed to have occurred if any
                 Person, a group or groups of related or unrelated Persons
                 acquires more than fifty-one percent (51%) in value of the oil
                 and gas properties of the Company pursuant to one or more
                 transactions with the Company during the term of this
                 Agreement.

                 "Beneficial Owner" shall have the meaning set forth in Rules
                 13d-3 and 13d-5 under the Securities Exchange Act of 1934, as
                 in effect on May 1, 1995.

                 A "Change in Control" shall be deemed to have occurred if (i)
                 any Person is or becomes the Beneficial Owner of securities of
                 the Company representing thirty percent (30%) or more of the
                 Voting Power, (ii) there shall occur a change in the
                 composition of a majority of the Board within any period of
                 four (4) consecutive years which change shall not have been
                 approved by a majority of the Board as constituted immediately
                 prior to such change in composition, (iii) at any meeting of
                 the shareholders of the Company called for the purpose of
                 electing directors, more than one of the persons nominated by
                 the Board for election as directors shall fail to be elected,
                 or (iv) the consummation of a merger, consolidation, sale of
                 substantially all assets or other reorganization of the
                 Company, other than a reincorporation, in which the Company
                 does not survive.

                 "Person" shall have the meaning set forth in Sections 3(a)(9)
                 and 13(d)(3) of the Securities Exchange Act of 1934, as in
                 effect on May 1, 1995.





                                      -2-
<PAGE>   6
                 "Present Value" shall be calculated by utilizing a discount
                 factor equal to the prime rate published by The Chase
                 Manhattan Bank, N.A. as of the date of Termination of
                 employment.

                 The "Recapitalization" shall be deemed to have occurred if the
                 capital structure of the Company is changed in respect of the
                 holders of its debt securities which may involve a Change of
                 Control.

                 "Voting Power" shall mean the voting power of the outstanding
                 securities of the Company having the right under ordinary
                 circumstances to vote at an election of the Board.

         3.      Except as expressly amended hereby, the Agreement shall remain
                 in full force and effect in accordance with its terms.

         IN WITNESS WHEREOF, the Company and the Executive have executed this
Amendment on the date first written above.

                                        PRESIDIO OIL COMPANY





                                        By: /s/ Judson Williams              
                                            ----------------------------------
                                            Judson Williams, Treasurer

                                        EXECUTIVE
                                                                     




                                        By: /s/ Robert L. Smith              
                                            ----------------------------------
                                            Robert L. Smith





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