AMENDING AGREEMENT

         THIS AMENDING AGREEMENT made as of the 30th day of April, 2004

BETWEEN:

                ULTIMA ENERGY TRUST, a trust created under the Laws of
                the Province of Alberta, (hereinafter referred to as
                "Ultima")

                                     - and -

                ULTIMA VENTURES CORP., a corporation subsisting under
                the Laws of the Province of Alberta, (hereinafter
                referred to as "Ultima Co")

                                     - and -

                PETROFUND ENERGY TRUST, a trust created under the Laws
                of the Province of Ontario, (hereinafter referred to
                as "Petrofund")

                                     - and -

                PETROFUND CORP., a corporation subsisting under the
                Laws of the Province of Alberta, (hereinafter referred
                to as "Petrofund Co")


         WHEREAS Ultima, Ultima Co, Petrofund and Petrofund Co entered into a
combination agreement (the "Combination Agreement") dated March 29, 2004;

         AND WHEREAS Ultima, Ultima Co, Petrofund and Petrofund Co have agreed
to effect certain amendments to the Combination Agreement as more particularly
set out in this agreement (the "Amending Agreement");

         NOW THEREFORE THIS AGREEMENT WITNESSETH that in consideration of the
covenants and agreements herein contained and other good and valuable
consideration (the receipt and sufficiency of which are hereby acknowledged),
the parties hereto do hereby covenant and agree as follows:

                                    ARTICLE 1
                                 INTERPRETATION

1.1      Capitalized terms used herein, including the recitals hereto, which are
         defined in the Combination Agreement, shall have the meanings ascribed
         thereto in this Amending Agreement.

1.2      Any provision of this Amending Agreement which may be invalid shall be
         ineffective to the extent of such invalidity only, without affecting
         the validity of the remaining provisions of this Amending Agreement or
         the Combination Agreement as amended



                                      -2-

         hereby, it being the intent and purpose that the Combination
         Agreement, as amended by this Amending Agreement should survive and be
         valid to the maximum extent permitted by applicable law.

                                    ARTICLE 2
                                    AMENDMENT

2.1      The Combination Agreement shall be amended as follows:

         (a) the reference to Schedule "A" in the definition of "Assumption
             Agreement" shall be removed and replaced with "Schedule B-1";

         (b) the reference to June 9, 2004 in the definition of "Closing Date"
             shall be removed and replaced with "June 16, 2004";

         (c) after the definition of "Public Record", the following definition
             shall be inserted:

                    "Registration Statement" has the meaning ascribed thereto in
                    Section 2.13;"

         (d) subsection (d) in the definition of "Required Regulatory
             Approvals" shall be removed and replaced with the following:

                    "(d)  the Registration Statement shall have been declared
                          effective by the SEC under the U.S. Securities Act
                          and no stop order suspending the effectiveness of the
                          Registration Statement shall have been issued by the
                          SEC and no proceeding for that purpose shall have
                          been initiated by the SEC;"

         (e) section 2.13 shall be deleted and replaced with the following:

                    "The Petrofund Parties (with the cooperation of the Ultima
                    Parties) shall prepare and file with the SEC a registration
                    statement on Form F-10 (together with all amendments
                    thereto, the "Registration Statement"), in which the Ultima
                    Circular and any other documents used to solicit votes of
                    Ultima Unitholders at the Ultima Special Meeting shall be
                    included as a prospectus, in connection with the
                    registration under the Securities Act of the Payment Units
                    to be issued to the Ultima Unitholders pursuant to the
                    Acquisition and Redemption Transaction. The Petrofund
                    Parties and the Ultima Parties each shall use their
                    reasonable commercial efforts to cause the Registration
                    Statement to become effective as promptly as practicable
                    after the filing of the Ultima Circular with the Securities
                    Authorities. Until such time as the Registration Statement
                    has been filed, the Ultima Circular shall not be mailed to,
                    or otherwise used to solicit, Ultima Unitholders. Ultima
                    shall furnish all information concerning itself and its



                                      -3-

                    affiliates that Petrofund may reasonably request in
                    connection with such actions and the preparation of the
                    Registration Statement, including a reconciliation of any
                    Ultima financial statements (including pro forma financial
                    information of Ultima which gives effect to the purchase of
                    all of the issued and outstanding common shares and
                    preferred shares in the capital of Trioco Resources Inc.) to
                    be included in the Ultima Circular to U.S. generally
                    accepted accounting principles as required by Item 17 of
                    Form 20-F of the Exchange Act which shall be included within
                    the Ultima Circular. Petrofund will advise Ultima promptly
                    after it receives notice thereof, of the time when the
                    Registration Statement has become effective or any
                    supplement or amendment has been filed, of the issuance of
                    any stop order, or of any request by the SEC for amendment
                    of the Registration Statement or comments thereon and
                    responses thereto or requests by the SEC for additional
                    information. If, at any time prior to the Time of Closing,
                    any event or circumstance relating to the Ultima Parties, or
                    their respective officers or directors, should be discovered
                    by the Ultima Parties which should be set forth in an
                    amendment or a supplement to the Ultima Circular and the
                    Registration Statement, Ultima shall promptly inform
                    Petrofund. In connection with the filing of the Registration
                    Statement, Petrofund shall file with the SEC a written
                    irrevocable consent and power of attorney on Form F-X."

         (f) section 3.1(a) shall be deleted and replaced with the following:

                    "(a)  cause the Payment Units which are to be issued to
                          Ultima and then to be received by Ultima Unitholders
                          in exchange for the Ultima Units pursuant to the
                          Acquisition and Redemption Transaction not to be
                          subject to any trading restrictions under Applicable
                          Canadian Securities Laws or U.S. Securities Laws
                          (other than Control Person Restrictions and Affiliate
                          Restrictions) and to be listed and posted for trading
                          on the TSX and the AMEX (subject to notice of
                          issuance) by the Closing Date;"

         (g) section 3.2(a) shall be deleted and replaced with the following:

                    "(a)  cause the Payment Units which are to be issued to
                          Ultima and then to be received by Ultima Unitholders
                          in exchange for the Ultima Units pursuant to the
                          Acquisition and Redemption Transaction not to be
                          subject to any trading restrictions under Applicable
                          Canadian Securities Laws or U.S. Securities Laws
                          (other than Control Person Restrictions and
                          Affiliate Restrictions) and to be listed and posted
                          for trading on the TSX and the AMEX (subject to
                          notice of issuance) by the Closing Date;"



                                      -4-

         (h) section 3.2(b) shall be deleted and replaced with the following:

                    "(b)  until the earlier of (i) two years from the date
                          of the issuance of the Payment Units and (ii) the
                          date as of which none of the outstanding Payment
                          Units are subject to restrictions on their resale
                          pursuant to Rule 145 under the U.S. Securities Act,
                          make available adequate current public information
                          with respect to Petrofund as required by Rule 144
                          adopted by the SEC under the U.S. Securities Act;"

         (i) section (vv) of Schedule "C" shall be deleted and replaced with
             the following:

                    "(vv) Eligibility Requirements. Ultima meets the general
                          eligibility requirements for use of Form F-10
                          under the U.S. Securities Act."

         (j) section (xx) of Schedule "C" shall be deleted and replaced with
             the following:

                    "(xx) Information Contained in Ultima Circular. The
                          information in the Ultima Circular (excluding any
                          information therein provided by the Petrofund Parties)
                          and the information supplied by the Ultima Parties for
                          inclusion in the Registration Statement shall not at
                          (i) the time the Registration Statement becomes
                          effective, (ii) the time the Ultima Circular
                          (or any amendment thereof or supplement thereto) is
                          first mailed to the Ultima Unitholders, (iii) the time
                          of the Ultima Special Meeting and (iv) at the Time of
                          Closing contain any untrue statement of a material
                          fact or fail to state any material fact required to
                          be stated therein or necessary in order to make the
                          statements therein, in light of the circumstances
                          under which they were made, not misleading."

         (k) section (gg) of Schedule "D" shall be deleted and replaced with
             the following and all subsequent sections in Schedule "D" shall be
             re-ordered:

                    "(gg) Eligibility Requirements. Petrofund meets the general
                          eligibility requirements for use of Form F-10 under
                          the U.S. Securities Act.

                    (hh) Information Contained in Ultima Circular. The
                         information supplied by Petrofund Parties for inclusion
                         in the Ultima Circular or otherwise for inclusion in
                         the Registration Statement shall not at (i) the time
                         the Registration Statement becomes effective,
                         (ii) the time the Ultima Circular (or any amendment
                         thereof or supplement thereto) is first mailed to the
                         Ultima Unitholders, (iii) the time of the Ultima
                         Special Meeting and (iv) at the Time of Closing
                         contain any untrue statement of a material fact or
                         fail to



                                      -5-

                         state any material fact required to be stated therein
                         or necessary in order to make the statements therein,
                         in light of the circumstances under which they were
                         made, not misleading.

                    (ii) Compliance with U.S. Securities Act. The Registration
                         Statement and the Form F-X, and any amendments or
                         supplements thereto, shall, at the time (i) when each
                         became effective and (ii) at the Time of Closing,
                         comply in all material respects, with the requirements
                         of the U.S. Securities Act; provided, however, that,
                         except as otherwise provided herein, the Petrofund
                         Parties make no representation as to the compliance
                         with applicable Law of information included in the
                         Registration Statement with respect to, or provided by,
                         the Ultima Parties, including the information
                         contained in the Ultima Circular."

                                   ARTICLE 3
                                     WAIVER

3.1      The Petrofund Parties hereby waive the inaccuracies in the
         representations and warranties of the Ultima Parties contained in
         sections (vv) and (xx) of Schedule "C" of the Combination Agreement and
         acknowledge that such inaccuracies have been rectified by this Amending
         Agreement.

                                    ARTICLE 4
                                  MISCELLANEOUS

4.1      This Amending Agreement together with the provisions of the Combination
         Agreement constitute the entire agreement between the Parties, and for
         greater certainty, other than as specifically provided in this Amending
         Agreement, the provisions of the Combination Agreement remain in full
         force and effect and unamended.

4.2      Notwithstanding the date of execution hereof, the effective date of
         this amendment to the Combination Agreement and exhibits thereto shall
         be March 29, 2004 and all references to the Combination Agreement and
         exhibits thereto dated March 29, 2004 shall be deemed to include this
         document.

4.3      This Amending Agreement may be executed in one or more counterparts,
         each of which shall be deemed an original, but all of which together
         shall constitute one and the same instrument.

4.4      The Parties hereto acknowledge that, with respect to Ultima being a
         party to this Agreement, Ultima Co is entering into this Amending
         Agreement solely in its capacity as agent on behalf of Ultima and the
         obligations of Ultima hereunder shall not be personally binding upon
         the Ultima Trustee, Ultima Co or any of the Ultima Unitholders or any
         annuitant under a plan of which a unitholder is a trustee or carrier
         (an "annuitant") and



                                      -6-

         that any recourse against Ultima, Ultima Trustee, Ultima Co or any
         unitholder or annuitant in any manner in respect of any indebtedness,
         obligation or liability of Ultima arising hereunder or arising in
         connection herewith or from the matters to which this Amending
         Agreement relates, if any, including without limitation claims based on
         negligence, tortious behaviour or otherwise, shall be limited to, and
         satisfied only out of, the Trust Fund as defined in the Ultima Trust
         Indenture.

4.5      The obligations or liabilities, if any, of the Petrofund Trustee or
         Petrofund hereunder shall not be binding upon, nor shall resort be had
         to the property of, any of the unitholders or annuitants of Petrofund
         and such obligations and liabilities shall not be binding upon such
         unitholders or annuitants. The obligations or liabilities, if any, of
         the Petrofund Trustee or Petrofund hereunder shall be satisfied only
         out of the property of Petrofund and no resort may be had to the
         property of any trustee, manager, officer or employee of Petrofund or
         any director, officer or employee of any manager or trustee of
         Petrofund. The obligations and liabilities hereunder, if any, of any
         trustee, manager, officer or employee of Petrofund or any director,
         officer or employee of any manager or trustee of Petrofund shall bind
         such obligor only to the extent that such obligor is entitled to be
         indemnified by Petrofund. The provisions of this paragraph shall enure
         to the benefit of the heirs, successors, assigns and personal
         representatives of the trustee, manager, officer or employee of
         Petrofund, of any director, officer or employee of any manager or
         trustee of Petrofund, of the unitholders and annuitants of Petrofund
         and, to the extent necessary to provide effective enforcement of such
         provisions, the Petrofund Trustee is hereby acknowledged to be acting,
         and shall be entitled to act as, trustee for the unitholders and
         annuitants of Petrofund.



                                      -7-

IN WITNESS WHEREOF, the parties hereto have executed this Amending Agreement the
30th day of April, 2004.


ULTIMA ENERGY TRUST, by Ultima              PETROFUND ENERGY TRUST, by
Ventures Corp.                              Petrofund Corp.


Per:                                        Per:
    ----------------------------                 -------------------------------
     Name:                                        Name:
     Title:                                       Title:


Per:                                        Per:
    ----------------------------                 -------------------------------
     Name:                                        Name:
     Title:                                       Title:


ULTIMA VENTURES CORP.                       PETROFUND CORP.




Per:                                        Per:
    ----------------------------                 -------------------------------
     Name:                                        Name:
     Title:                                       Title:


Per:                                        Per:
    ----------------------------                 -------------------------------
     Name:                                        Name:
     Title:                                       Title: