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                                                                    EXHIBIT 10.3


            MORTGAGE, ASSIGNMENT, SECURITY AGREEMENT, FIXTURE FILING
                            AND FINANCING STATEMENT

                                      FROM

                           PERFORMANCE PETROLEUM CO.,
                     UNITED STATES GAS GATHERING CO., INC.
                                      AND
                              PACIFIC OSAGE, INC.

                                       TO

                     ING (U.S.) CAPITAL CORPORATION, Agent


                               Dated May 15, 1998


A CARBON, PHOTOGRAPHIC, FACSIMILE, OR OTHER REPRODUCTION OF THIS INSTRUMENT IS
SUFFICIENT AS A FINANCING STATEMENT.

THIS INSTRUMENT CONTAINS AFTER-ACQUIRED PROPERTY PROVISIONS, SECURES PAYMENT OF
FUTURE ADVANCES, AND COVERS PROCEEDS OF COLLATERAL.

THIS INSTRUMENT COVERS MINERALS AND OTHER SUBSTANCES OF VALUE WHICH MAY BE
EXTRACTED FROM THE EARTH (INCLUDING WITHOUT LIMITATION OIL AND GAS), AND THE
ACCOUNTS RELATED THERETO, WHICH WILL BE FINANCED AT THE WELLHEADS OR MINEHEADS
OF THE WELLS OR MINES LOCATED ON THE PROPERTIES DESCRIBED IN SECTION 1.1 OF
THIS INSTRUMENT.  THIS INSTRUMENT COVERS GOODS WHICH ARE OR ARE TO BECOME
FIXTURES ON THE REAL PROPERTY DESCRIBED HEREIN.  THIS INSTRUMENT IS TO BE FILED
FOR RECORD, AMONG OTHER PLACES, IN THE REAL ESTATE OR COMPARABLE RECORDS OF THE
COUNTIES AND/OR PARISHES REFERENCED IN EXHIBIT A HERETO AND SUCH FILING SHALL
SERVE, AMONG OTHER PURPOSES, AS A FIXTURE FILING.  THE MORTGAGOR HAS AN
INTEREST OF RECORD IN THE REAL ESTATE AND IMMOVABLE PROPERTY CONCERNED, WHICH
INTEREST IS DESCRIBED IN SECTION 1.1 OF THIS INSTRUMENT.

A POWER OF SALE HAS BEEN GRANTED IN THIS MORTGAGE.  A POWER OF SALE MAY ALLOW
MORTGAGEE (AS HEREINAFTER DEFINED) TO TAKE THE MORTGAGED PROPERTIES AND SELL
THEM WITHOUT GOING TO COURT IN A FORECLOSURE ACTION UPON DEFAULT BY THE
MORTGAGOR (AS HEREINAFTER DEFINED) UNDER THIS MORTGAGE.


WHEN RECORDED OR FILED RETURN TO:                  THIS DOCUMENT PREPARED BY:

Thompson & Knight, P.C.                            Arthur J. Wright
1700 Pacific Avenue                                Thompson & Knight, P.C.
Suite 3300                                         1700 Pacific Avenue
Dallas, Texas  75201                               Suite 3300
Attention:  Arthur J. Wright                       Dallas, Texas  75201
<PAGE>   2
                   MORTGAGE, ASSIGNMENT, SECURITY AGREEMENT,
           FIXTURE FILING AND FINANCING STATEMENT (this "Mortgage"),


                                   ARTICLE I.

                     Granting Clauses; Secured Indebtedness

         Section 1.1.  Lien of Mortgage.   Performance Petroleum Co., United
States Gas Gathering Co., Inc. and Pacific Osage, Inc. (herein collectively
called "Mortgagor"), in order to secure the payment of the secured indebtedness
hereinafter referred to and the performance of the obligations, covenants,
agreements, warranties and undertakings of Mortgagor hereinafter described,
does hereby MORTGAGE to ING U.S. Capital Corporation, Agent  (herein called
"Mortgagee"), and grant to Mortgagee a POWER OF SALE (pursuant to this Mortgage
and applicable law) with respect to, the following (the "Mortgaged
Properties"):

                 A.       The oil, gas and/or other mineral leases or
         properties which are described in Exhibit A attached hereto and made a
         part hereof;

                 B.       Without limitation of the foregoing, all other right,
         title and interest of Mortgagor of whatever kind or character (whether
         now owned or hereafter acquired by operation of law or otherwise) in
         and to (i) the oil, gas and/or mineral leases or other agreements
         described in Exhibit A hereto and (ii) the lands described or referred
         to in Exhibit A (or described in any of the instruments described or
         referred to in Exhibit A), without regard to any limitations as to
         specific lands or depths that may be set forth in Exhibit A hereto or
         in any of the leases or other agreements described in Exhibit A
         hereto.

                 C.       All of Mortgagor's interest (whether now owned or
         hereafter acquired by operation of law or otherwise) in and to all
         presently existing and hereafter created oil, gas and/or mineral
         unitization, pooling and/or communitization agreements, declarations
         and/or orders, and in and to the properties, rights and interests
         covered and the units created thereby (including, without limitation,
         units formed under orders, rules, regulations or other official acts
         of any federal, state or other authority having jurisdiction), which
         cover, affect or otherwise relate to the properties, rights and
         interests described in clause A or B above;

                 D.       The rights, interests and estates created under those
         certain servitudes, easements, rights of way, privileges, franchises,
         prescriptions, licenses, leases, permits and/or other rights described
         in Exhibit A, attached hereto and made a part hereof, together with
         any amendments, renewals, extensions, supplements, modifications or
         other agreements related thereto and further together with any other
         servitudes, easements, rights of way, privileges, prescriptions,
         franchises, licenses, permits and/or other rights used, held for use
         in connection with, or in any way related to the "Gathering Systems"
         (as hereinafter defined);

                 E.       All gathering systems located on the properties
         described in clauses A or D above, all gathering systems depicted on
         the maps attached as Exhibit B hereto and made a part hereof and all
         rights of Mortgagor in other gathering systems located in Sections,
         Townships and Ranges described on Exhibit C attached hereto and made a
         part hereof; (such systems including all pipes, valves, gauges, meters
         and other measuring equipment, regulators, extractors, tubing,
         pipelines, fuel lines, facilities, improvements, fittings, materials
         and other improvements, fixtures and/or personal property) (the
         properties, rights and interests described in this item E, are herein
         collectively called the "Gathering Systems");

                 F.       All of Mortgagor's interest in and rights under
         (whether now owned or hereafter acquired by operation of law or
         otherwise) all presently existing and hereafter created operating
         agreements, equipment leases, production sales contracts, processing
         agreements, transportation agreements, gas balancing agreements,
         farmout and/or farm-in agreements, salt water disposal agreements,
         area of mutual interest agreements, and other


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         contracts and/or agreements which cover, affect, or otherwise relate
         to the properties, rights and interests described in clause A, B, C, D
         or E above or to the operation of such properties, rights and
         interests or to the treating, handling, storing, processing,
         transporting or marketing of oil, gas, other hydrocarbons, or other
         minerals produced from (or allocated to) such properties, rights and
         interests including, but not limited to, those contracts listed in
         Exhibit A hereto, as same may be amended or supplemented from time to
         time;

                 G.       All of Mortgagor's interest (whether now owned or
         hereafter acquired by operation of law or otherwise) in and to all
         improvements, fixtures, movable or immovable property and other real
         and/or personal property (including, without limitation, all wells,
         pumping units, wellhead equipment, tanks, pipelines, flow lines,
         gathering lines, compressors, dehydration units, separators, meters,
         buildings, injection facilities, salt water disposal facilities, and
         power, telephone and telegraph lines) and all easements, servitudes,
         rights-of-way, surface leases, licenses, permits and other surface
         rights, which are now or hereafter used, or held for use, in
         connection with the properties, rights and interests described in
         clause A, B, C, D or E above, or in connection with the operation of
         such properties, rights and interests, or in connection with the
         treating, handling, storing, processing, transporting or marketing of
         oil, gas, other hydrocarbons, or other minerals produced from (or
         allocated to) such properties, rights and interests; and

                 H.       All rights, estates, powers and privileges
         appurtenant to the foregoing rights, interests and properties.

         TO HAVE AND TO HOLD the Mortgaged Properties unto Mortgagee, and
Mortgagee's heirs, devisees, representatives, successors and assigns, upon the
terms, provisions and conditions herein set forth.

         Section 1.2.  Grant of Security Interest.  In order to further secure
the payment of the secured indebtedness hereinafter referred to and the
performance of the obligations, covenants, agreements, warranties, and
undertakings of Mortgagor hereinafter described, Mortgagor hereby grants to
Mortgagee a security interest in the entire interest of Mortgagor (whether now
owned or hereafter acquired by operation of law or otherwise) in and to:

                 (a)      all oil, gas, other hydrocarbons, and other minerals
         produced from or allocated to the Mortgaged Properties, and any
         products processed or obtained therefrom (herein collectively called
         the "Production"), together with all proceeds of such Production
         (regardless of whether such Production to which such proceeds relate
         occurred on or before or after the date hereof ), and together with
         all liens and security interests securing payment of the proceeds of
         such Production, including, but not limited to, those liens and
         security interests provided for under (i) statutes enacted in the
         jurisdictions in which the Mortgaged Properties are located, or (ii)
         statutes made applicable to the Mortgaged Properties under federal law
         (or some combination of federal and state law);

                 (b)      without limitation of any other provisions of this
         Section 1.2, all payments received in lieu of such Production from the
         Mortgaged Properties (regardless of whether such payments accrued,
         and/or the events which gave rise to such payments occurred, on or
         before or after the date hereof), including, without limitation, "take
         or pay" payments and similar payments, payments received in settlement
         of or pursuant to a judgment rendered with respect to take or pay or
         similar obligations or other obligations under a production sales
         contract, payments received in buyout or buydown or other settlement
         of a production sales contract, and payments received under a gas
         balancing or similar agreement as a result of (or received otherwise
         in settlement of or pursuant to judgment rendered with respect to)
         rights held by Mortgagor as a result of Mortgagor (and/or its
         predecessors in title) taking or having taken less gas from lands
         covered by a Mortgaged Property (or lands pooled or unitized
         therewith) than their ownership of such Mortgaged Property would
         entitle them to receive (the payments described in this subsection (b)
         being herein called "Payments in Lieu of Production");





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                 (c)      all equipment, inventory, improvements, fixtures,
         accessions, goods and other personal property or movable property of
         whatever nature now or hereafter located on or used or held for use in
         connection with the Mortgaged Properties (or in connection with the
         operation thereof or the treating, handling, storing, processing,
         transporting, or marketing of Production), and all licenses and
         permits of whatever nature now or hereafter used or held for use in
         connection with the Mortgaged Properties (or in connection with the
         operation thereof, or the treating, handling, storing, processing,
         transporting or marketing of Production), and all renewals or
         replacements of the foregoing or substitutions for the foregoing;

                 (d)      all contract rights, choses in action (i.e., rights
         to enforce contracts or to bring claims thereunder) and other general
         intangibles (regardless of whether the same arose, and/or the events
         which gave rise to the same occurred, on or before or after the date
         hereof) related to the Mortgaged Properties, the operation thereof
         (whether Mortgagor is operator or non-operator), or the treating,
         handling, storing, processing, transporting, or marketing of
         Production (including, without limitation, any of the same relating to
         payment of proceeds of Production or to payment of amounts which could
         constitute Payments in Lieu of Production);

                 (e)      without limitation of the generality of the
         foregoing, any rights and interests of the Mortgagor under any present
         or future hedge or swap agreements, cap, floor, collar, exchange,
         forward or other hedge or protection agreements or transactions
         relating to crude oil, natural gas or other hydrocarbons, or any
         option with respect to any such agreement or transaction now existing
         or hereafter entered into by or on behalf of Mortgagor;

                 (f)      all geological, geophysical, engineering, accounting,
         title, legal, and other technical or business data concerning the
         Mortgaged Properties, the Production, or any other item of Property
         (as hereinafter defined) which are now or hereafter in the possession
         of Mortgagor or in which Mortgagor can otherwise grant a security
         interest, and all books, files, records, magnetic media, and other
         forms of recording or obtaining access to such data;

                 (g)      all money, documents, instruments, chattel paper,
         securities, accounts or general intangibles arising from or by virtue
         of any transaction (regardless of whether such transaction occurred on
         or before or after the date hereof ) including without implied
         limitation those transactions related to the Mortgaged Properties, the
         Production or any other item of Property (all of the properties,
         rights and interests described in subsections (a), (b), (c), (d), (e)
         and (f) above and this subsection (g) being herein sometimes
         collectively called the "Collateral"); and

                 (h)      all proceeds of the Collateral, whether such proceeds
         or payments are goods, money, documents, instruments, chattel paper,
         securities, accounts, general intangibles, fixtures, real/immovable
         property, personal/movable property or other assets (the Mortgaged
         Properties, the Collateral and the proceeds of the Collateral being
         herein sometimes collectively called the "Property").

         Section 1.3.  Note, Loan Documents, Other Obligations.  This Mortgage
is made to secure and enforce the payment and performance of the following
promissory notes, obligations, indebtedness and liabilities:

                 (a)      All indebtedness and other obligations now or
         hereafter incurred or arising pursuant to the provisions of that
         certain Credit Agreement dated of even date herewith between United
         States Exploration, Inc.  ("Borrower") and Mortgagee and all
         supplements thereto and amendments or modifications thereof, and all
         agreements given in substitution therefor or in restatement, renewal
         or extension thereof, in whole or in part (such Credit Agreement as
         the same may from time to time be supplemented, amended or modified,
         and all other agreements given in substitution therefor or in
         restatement, renewal or extension thereof, in whole or in part, being
         herein called the "Credit Agreement");





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                 (b)      One certain promissory note dated of even date
         herewith, in the principal amount of Thirty-five Million Dollars
         ($35,000,000) made by Borrower and payable to the order of ING
         Capital, on or before December 31, 2004, bearing interest as therein
         provided, and containing a provision for the payment of a reasonable
         additional amount as attorneys' fees, as the same may from time to
         time be supplemented, amended or modified, and all other notes given
         in substitution therefor or in modification, renewal or extension
         thereof, in whole or in part (such note, as from time to time
         supplemented, amended, or modified and all other notes given in
         substitution therefor, or in modification, renewal or extension
         thereof, in whole or in part, being herein called the "Note");

                 (c)      That certain Guaranty, dated of even date herewith,
         executed by Performance Petroleum Co., as the same may from time to
         time be supplemented, amended or modified, and all other instruments
         given in substitution therefor or in modification, renewal or
         extension thereof, in whole or in part.

                 (d)      That certain Guaranty, dated of even date herewith,
         executed by United States Gas Gathering Co., as the same may from time
         to time be supplemented, amended or modified, and all other
         instruments given in substitution therefor or in modification, renewal
         or extension thereof, in whole or in part.

                 (e)      That certain Guaranty, dated of even date herewith,
         executed by Pacific Osage, Inc., as the same may from time to time be
         supplemented, amended or modified, and all other instruments given in
         substitution therefor or in modification, renewal or extension
         thereof, in whole or in part.

                 (f)      All indebtedness and other obligations now or
         hereafter incurred or arising pursuant to or permitted by the
         provisions of the Note, the above described guarantees, the Credit
         Agreement, this Mortgage or any other instrument now or hereafter
         evidencing, governing, guaranteeing or securing the "secured
         indebtedness" (as hereinafter defined) or any part thereof or
         otherwise executed in connection with any advance or loan evidenced or
         governed by the Note, such guarantees or the Credit Agreement (the
         Note, such guarantees, the Credit Agreement, this Mortgage and such
         other instruments being herein sometimes collectively called the "Loan
         Documents");

                 (g)      All present or future "Hedging Obligations" incurred
         or owing by Borrower or any Mortgagor to any one or more members of
         the "Credit Group," as hereinafter defined; as used in this paragraph
         and the following paragraph (e): (i) "Credit Group" means ING (U.S.)
         Capital Corporation, any other party from time to time constituting a
         lender under the Credit Agreement, and/or any affiliate of any such
         party, including without limitation Internationale Nederlanden (U.S.)
         Capital Markets, Inc., being an affiliate of ING (U.S.) Capital
         Corporation, and (ii) "Hedging Obligations" means any indebtedness or
         obligations, however arising, to make payments or take actions under
         or pursuant to any present or future agreement (including any
         individual agreement or any master agreement and the various
         transactions and confirmations made thereunder) governing any swap,
         put, call, cap, floor or collar transaction, or other type of
         agreement or transaction relating to interest rates, currency exchange
         rates, or the price or delivery (at any one or more locations or in
         any one or more markets) of crude oil, natural gas, natural gas
         liquids, petroleum products, other hydrocarbons, agricultural
         products, precious metals, stocks or bonds or indices thereof, or any
         other commodity, contract or other item of property traded in any
         market, and all interest thereon and expenses and other amounts
         payable in connection therewith (any agreement or document, however
         entitled or described, evidencing or governing and Hedging Obligations
         owing by Borrower or any Mortgagor to any one or more members of the
         Credit Group being herein called a "Hedging Agreement");

                 (h)      All present or future indebtedness or obligations
         incurred or owing to any one or more members of the Credit Group by
         Borrower or any Mortgagor, however arising, to make reimbursements or
         similar payments to any one or more members of the Credit Group as a
         result of or relating to any payments made by any one or more members
         of the Credit Group to any third person on account of or for the
         benefit of Borrower or any Mortgagor, including without limitation any
         obligation to reimburse any one or more members of the Credit Group
         for payments it makes under or pursuant to any letter of credit, bond,
         guaranty,





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         or indemnity agreement issued or made for the account of or for the
         benefit of Borrower or any Mortgagor (such as a letter of credit,
         guaranty or indemnity by any one or more members of the Credit Group
         of any Hedging Obligations owed by Borrower or any Mortgagor to a
         third person) and all interest thereon and expenses and other amounts
         payable in connection therewith (any agreement or document, however
         entitled or described, evidencing or governing any such indebtedness
         or obligation owing to any one or more members of the Credit Group by
         Borrower or any Mortgagor being herein called a "Reimbursement
         Agreement");

                 (i)      All other loans and future advances made by Mortgagee
         to Borrower or any Mortgagor and all other debts, obligations and
         liabilities of Borrower or any Mortgagor of every kind and character
         now or hereafter existing in favor of Mortgagee, whether direct or
         indirect, primary or secondary, joint or several, fixed or contingent,
         and whether originally payable to Mortgagee or to a third party and
         subsequently acquired by Mortgagee, it being contemplated that
         Borrower and/or any Mortgagor may hereafter become indebted to
         Mortgagee for such further debts, obligations and liabilities; and

                 (j)      Without limiting the generality of the foregoing, all
         post-petition interest, expenses, and other duties and liabilities
         with respect to indebtedness or other obligations described above in
         this Section 1.3, which would be owed but for the fact that they are
         unenforceable or not allowable due to the existence of a bankruptcy,
         reorganization, or similar proceeding.

         Section 1.4.  Secured Indebtedness.  The indebtedness referred to in
Section 1.3, and all renewals, extensions and modifications thereof, and all
substitutions therefor, in whole or in part, are herein sometimes referred to
as the "secured indebtedness" or the "indebtedness secured hereby".

         Section 1.5.  Limit on Secured Indebtedness.  It is the intention of
Mortgagor and Mortgagee that this Mortgage not constitute a fraudulent transfer
or fraudulent conveyance under any state or federal law that may be applied
hereto.  Mortgagor and, by its acceptance hereof, Mortgagee hereby acknowledges
and agrees that, notwithstanding any other provision of this Mortgage, the
amount of indebtedness secured hereby shall be limited to the maximum amount of
indebtedness that can be secured by Mortgagor hereunder without rendering this
Mortgage voidable under applicable law relating to fraudulent conveyances or
fraudulent transfers.


                                  ARTICLE II.

                   Representations, Warranties and Covenants

         Section 2.1.  Mortgagor represents, warrants, and covenants as
follows:

                 (a)      Title and Permitted Encumbrances.  Mortgagor has, and
         Mortgagor covenants to maintain, good and defensible title to the
         Property, free and clear of all liens, security interests, and
         encumbrances except for (i) the contracts, agreements, burdens,
         encumbrances and other matters set forth in the descriptions of
         certain of the Mortgaged Properties on Exhibit A hereto, (ii) the
         liens and security interests evidenced by this Mortgage, (iii)
         statutory liens for taxes which are not yet delinquent, (iv) liens
         under operating agreements, pooling orders and unitization agreements,
         and mechanics' and materialmen's liens, with respect to obligations
         which are not more than 90 days past due, and (v) other liens and
         security interests (if any) in favor of





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         Mortgagee (the matters described in the foregoing clauses (i), (ii),
         (iii), (iv), and (v) being herein called the "Permitted
         Encumbrances"); Mortgagor will warrant and defend title to the
         Property, subject as aforesaid, against the claims and demands of all
         persons claiming or to claim the same or any part thereof.  The
         ownership by Mortgagor of the Mortgaged Properties does and will, with
         respect to each well or unit identified on Exhibit A, attached hereto
         and made a part hereof, entitle Mortgagor to receive (subject to the
         terms and provisions of this Mortgage) a decimal or percentage share
         of the oil, gas and other hydrocarbons produced from, or allocated to,
         such well or unit equal to not less than the decimal or percentage
         share set forth, for such well or unit, opposite the designation "NRI"
         on Exhibit A, and cause Mortgagor to be obligated to bear a decimal or
         percentage share of the cost of operation of such well or unit equal
         to not more than the decimal or percentage share set forth, for such
         well or unit, opposite the designation "WI" on Exhibit A.  The
         above-described shares of production which Mortgagor is entitled to
         receive, and shares of expenses which Mortgagor is obligated to bear,
         are not and will not be subject to change except, and only to the
         extent that, such changes are reflected in Exhibit A.  There is not
         and will not be any unexpired financing statement covering any part of
         the Property on file in any public office naming any party other than
         Mortgagee as secured party.  Upon request by Mortgagee, Mortgagor will
         deliver to Mortgagee schedules of all internal and third party
         information identifying the Mortgaged Properties (such as, for
         example, lease names and numbers assigned by Mortgagor or the operator
         of any Mortgaged Property, well and/or unit and/or property names and
         numbers assigned by purchasers of Production, and internal
         identification names and numbers used by Mortgagor in accounting for
         revenues, costs, and joint interest transactions attributable to the
         Mortgaged Properties).

                 (b)      Leases and Contracts; Performance of Obligations.
         The oil, gas and/or mineral leases, contracts, servitudes and other
         agreements forming a part of the Property, to the extent the same
         cover or otherwise relate to the Property, are in full force and
         effect, and Mortgagor agrees to so maintain them in full force and
         effect.  All rents, royalties and other payments due and payable under
         such leases, contracts, servitudes and other agreements, or under the
         Permitted Encumbrances, or otherwise attendant to the ownership or
         operation of the Property, have been, and will continue to be,
         properly and timely paid.  Mortgagor is not in default with respect to
         Mortgagor's obligations (and Mortgagor is not aware of any default by
         any third party with respect to such third party's obligations) under
         such leases, contracts, servitudes and other agreements, or under the
         Permitted Encumbrances, or otherwise attendant to the ownership or
         operation of any part of the Property, where such default could
         adversely affect the ownership or operation of the Property; Mortgagor
         will fulfill all such obligations coming due in the future.

                 (c)      Sale of Production.  No Mortgaged Property is or will
         become subject to any contractual or other arrangement (i) whereby
         payment for production is or can be deferred for a substantial period
         after the month in which such production is delivered (i.e., in the
         case of oil, not in excess of 60 days, and in the case of gas, not in
         excess of 90 days) or (ii) whereby payments are made to Mortgagor
         other than by checks, drafts, wire transfer advises or other similar
         writings, instruments or communications for the immediate payment of
         money.  Except for production sales contracts, processing agreements
         or transportation agreements (or other agreements relating to the
         marketing of Production) listed on





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<PAGE>   8
         Exhibit A (in connection with the Mortgaged Properties to which they
         relate), (i) no Mortgaged Property is or will become subject to any
         contractual or other arrangement for the sale, processing or
         transportation of Production (or otherwise related to the marketing of
         Production) for a term longer than one year and (ii) all contractual
         or other arrangements for the sale, processing or transportation of
         Production (or otherwise related to the marketing of Production) shall
         be bona fide arm's length transactions with third parties not
         affiliated with Mortgagor and shall be at the best price (and on the
         best terms) then available (such price shall, in the case of
         Production sales which are subject to price controls, be determined
         giving consideration to such fact).  Neither Mortgagor, nor to the
         best of Mortgagor's knowledge any of its predecessors in title, has
         received prepayments (including, but not limited to, payments for gas
         not taken pursuant to "take or pay" or other similar arrangements) for
         any oil, gas or other hydrocarbons produced or to be produced from the
         Mortgaged Properties after the date hereof, and Mortgagor hereby
         covenants not to enter into any such advance or prepayment
         arrangements whereby it accepts consideration for oil, gas or other
         hydrocarbons not yet produced.  No Mortgaged Property is or will
         become subject to any "take or pay" or other similar arrangement (i)
         which can be satisfied in whole or in part by the production or
         transportation of gas from other properties or (ii) as a result of
         which production from the Mortgaged Properties may be required to be
         delivered to one or more third parties without payment (or without
         full payment) therefor as a result of payments made, or other actions
         taken, with respect to other properties.  The amount by which the
         volume of gas taken by Mortgagor and its predecessors in title prior
         to the date hereof exceeds the amount that its ownership interest in
         the Mortgage Properties would entitle it to take ("overproduced") is
         not greater than 250,000 MCF.  Mortgagor will not, after the date
         hereof, become "overproduced" (as above defined) with respect to any
         well on the Mortgaged Properties (or on any unit in which the
         Mortgaged Properties participate), in an amount in excess of
         Mortgagor's share of gas produced from such well during the preceding
         four calendar months plus ten percent (10%) of such actual production
         from any such well.  No Mortgaged Property is, or will become, subject
         to a gas balancing arrangement under which one or more third parties
         may take a portion of the production attributable to such Mortgaged
         Property without payment (or without full payment) therefor as a
         result of production having been taken from, or as a result of other
         actions or inactions with respect to, other properties.  No Mortgaged
         Property is subject, at the present time, to any regulatory refund
         obligation and, to the best of Mortgagor's knowledge, no facts exist
         which might cause the same to be imposed.

                 (d)      Condition of Personal or Movable Property.  Subject
         to ordinary wear and tear and any sales permitted by Paragraph 7.5 of
         the Credit Agreement or Paragraph (f) hereof, (i) the equipment,
         inventory, improvements, fixtures, goods and other tangible
         personal/movable property forming a part of the Property are and will
         remain in good repair and condition and are and will be adequate for
         the normal operation of the Property in accordance with prudent
         industry standards and (ii) all of such Property is, and will remain,
         located on the Mortgaged Properties, except for that portion thereof
         which is or shall be located elsewhere (including that usually located
         on the Mortgaged Properties but temporarily located elsewhere) in the
         course of the normal operation of the Property.





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<PAGE>   9
                 (e)      Operation of Mortgaged Properties.  The Mortgaged
         Properties (and properties unitized therewith) are being (and, to the
         extent the same could adversely affect the ownership or operation of
         the Mortgaged Properties after the date hereof, have in the past
         been), and hereafter will be, maintained, operated and developed in a
         good and workmanlike manner, in accordance with prudent industry
         standards and in conformity with all applicable laws and all rules,
         regulations and orders of all duly constituted authorities having
         jurisdiction and in conformity with all oil, gas and/or other mineral
         leases and other contracts and agreements forming a part of the
         Property and in conformity with the Permitted Encumbrances;
         specifically in this connection none of the wells located on the
         Mortgaged Properties (or properties unitized therewith) are, or will
         be, deviated from the vertical more than the maximum permitted by
         applicable laws, regulations, rules and orders, and such wells are,
         and will remain, bottomed under and producing from, with the well
         bores wholly within, the Mortgaged Properties (or, in the case of
         wells located on properties unitized therewith, such unitized
         properties).  The representation, warranties and covenants in the
         preceding sentence are made in the case of existing wells only as to
         Mortgagor's knowledge and in regard to future wells only where
         Mortgagor is the operator of such well.  Mortgagor has, and will have
         in the future, all governmental licenses and permits necessary or
         appropriate to own and operate the Property; and Mortgagor has not
         received notice of any violations in respect of any such licenses or
         permits.

                 (f)      Sale or Disposal.  Except for sales permitted by
         Paragraph 7.5 of the Credit Agreement, Mortgagor will not, without the
         prior written consent of Mortgagee, sell, exchange, lease, transfer,
         or otherwise dispose of any part of, or interest in, the Property
         other than (i) sales, transfers and other dispositions of machinery,
         equipment and other personal/movable property and fixtures made in
         connection with a release, surrender or abandonment (to which
         Mortgagee has given its prior written consent) of a lease, (ii) sales,
         transfers and other dispositions of machinery, equipment and other
         personal/movable property and fixtures in connection with the
         abandonment (to which Mortgagee has given its prior written consent)
         of a well, (iii) sales, transfers and other dispositions of machinery,
         equipment and other personal/movable property and fixtures which are
         (A) obsolete for their intended purpose and disposed of in the
         ordinary course of business or (B) replaced by articles of at least
         equal suitability and value owned by Mortgagor free and clear of all
         liens except this Mortgage and the Permitted Encumbrances, and (iv)
         sales of Production which are made in the ordinary course of business
         and in compliance with Section 2.1(c) hereof; provided that nothing in
         clause (iv) shall be construed as limiting Mortgagee's rights under
         Article III of this Mortgage.  Mortgagor shall account fully and
         faithfully for and, if Mortgagee so elects, shall promptly pay or turn
         over to Mortgagee the proceeds in whatever form received from
         disposition in any manner of any of the Property.  Mortgagor shall
         keep accurate and complete records of the Property and its proceeds.

                 (g)      Ad Valorem and Severance Taxes.  In regard to the
         Mortgaged Property which Mortgagor operates, Mortgagor, or the prior
         owner from whom it acquired the Mortgaged Property, has paid and
         discharged, and will continue to pay and discharge, all ad valorem
         taxes assessed against the Property or any part thereof and all
         production, severance and other taxes assessed against, or measured
         by, the Production or the value, or proceeds, of the Production.





                                       8
<PAGE>   10
                 (h)      Suits and Claims.  Except as scheduled or disclosed
         in the Credit Agreement, there are no suits, actions, claims,
         investigations, inquiries, proceedings or demands pending (or, to
         Mortgagor's knowledge, threatened) which affect the Property
         (including, without limitation, any which challenge or otherwise
         pertain to Mortgagor's title to the Property) and no judicial or
         administrative actions, suits or proceedings pending (or, to
         Mortgagor's knowledge, threatened) against Mortgagor.

                 (i)      Environmental.  Mortgagor will not cause or permit
         the Property or the Associated Property or Mortgagor to be in
         violation of, or do anything or permit anything to be done which will
         subject the Property or the Associated Property to any remedial
         obligations under, or result in noncompliance with applicable permits
         and licenses under, any Applicable Environmental Laws, assuming
         disclosure to the applicable governmental authorities of all relevant
         facts, conditions and circumstances, if any, pertaining to the
         Property or the Associated Property and Mortgagor will promptly notify
         Mortgagee in writing of any existing, pending or, to the best
         knowledge of Mortgagor, threatened investigation, claim, suit or
         inquiry by any governmental authority or any person in connection with
         any Applicable Environmental Laws.  Mortgagor will not cause or permit
         the disposal or other release of any hazardous substance or solid
         waste at, into, upon or under the Property or the Associated Property
         and covenants and agrees to keep or cause the Property and/or the
         Associated Property to be kept free of any hazardous substance or
         solid waste (except such use, and temporary storage in anticipation of
         use, as is required in the ordinary course of business, all while in
         compliance with Applicable Environmental Laws), and to remove the same
         (or if removal is prohibited by law, to take whatever action is
         required by law) promptly upon discovery at its sole expense.  Upon
         Mortgagee's reasonable request, at any time and from time to time
         during the existence of this Mortgage, Mortgagor will provide at
         Mortgagor's sole expense an inspection or audit of the Property and
         the Associated Property from an engineering or consulting firm
         approved by Mortgagee, indicating the presence or absence of hazardous
         substances and solid waste on the Property and/or the Associated
         Property and compliance with Applicable Environmental Laws.

                 (j)      Defense of Mortgage.  If the validity or priority of
         this Mortgage or of any rights, titles, liens or security interests
         created or evidenced hereby with respect to the Property or any part
         thereof or the title of Mortgagor to the Property shall be endangered
         or questioned or shall be attacked directly or indirectly or if any
         legal proceedings are instituted against Mortgagor with respect
         thereto, Mortgagor will give prompt written notice thereof to Lender
         and at Mortgagor's own cost and expense will diligently endeavor to
         cure any defect that may be developed or claimed, and will take all
         necessary and proper steps for the defense of such legal proceedings,
         including, but not limited to, the employment of counsel, the
         prosecution or defense of litigation and the release or discharge of
         all adverse claims, Lender, whether or not named as a party to legal
         proceedings with respect thereto), is hereby authorized and empowered
         to take such additional steps as in its judgment and discretion may be
         necessary or proper for the defense of any such legal proceedings or
         the protection of the validity or priority of this Mortgage and the
         rights, titles, liens and security interests created or evidenced
         hereby, including but not limited to the employment of independent
         counsel, the prosecution or defense of litigation, the compromise or
         discharge of any adverse claims made with respect to the





                                       9
<PAGE>   11
         Property, the purchase of any tax title and the removal of prior liens
         or security interests, and all expenditures so made of every kind and
         character shall be a demand obligation (which obligation Mortgagor
         hereby expressly promises to pay) owing by Mortgagor to Lender (as the
         case may be) and shall bear interest from the date expended until paid
         at the rate described in Section 2.3 hereof, and the party incurring
         such expenses shall be subrogated to all rights of the person
         receiving such payment.

                 (k)      Fees and Expenses; Indemnity.  Mortgagor will
         reimburse Mortgagee (for purposes of this paragraph, the term
         "Mortgagee" shall include the directors, officers, partners, employees
         and agents of Mortgagee and any persons or entities owned or
         controlled by or affiliated with Mortgagee) for all expenditures,
         including reasonable attorneys' fees and expenses, incurred or
         expended in connection with (i) the breach by Mortgagor of any
         covenant, agreement or condition contained herein or in any other Loan
         Document, (ii) the exercise of any rights and remedies hereunder or
         under any other Loan Document, and (iii) the protection of the
         Property and/or liens and security interests therein.  Mortgagor will
         indemnify and hold harmless Mortgagee from and against (and will
         reimburse Mortgagee for) all claims, demands, liabilities, losses,
         damages (including without limitation consequential damages), causes
         of action, judgments, penalties, costs and expenses (including without
         limitation reasonable attorneys' fees and expenses) which may be
         imposed upon, asserted against or incurred or paid by Mortgagee on
         account of, in connection with, or arising out of (A) any bodily
         injury or death or natural resource, human health or property damage
         occurring in, at, into, under or upon or in the vicinity of the
         Property through any cause whatsoever, (B) any act performed or
         omitted to be performed hereunder or the breach of any representation
         or warranty herein, (C) the exercise of any rights and remedies
         hereunder or under any other Loan Document, (D) any transaction, act,
         omission, event or circumstance arising out of or in any way connected
         with the Property or with this Mortgage or any other Loan Document,
         (E) any violation on or prior to the Release Date (as hereinafter
         defined) of any Applicable Environmental Law, (F) any act, omission,
         event or circumstance existing or occurring on or prior to the Release
         Date (including without limitation the presence on or under the
         Property or the Associated Property or release at, into, upon, under
         or from the Property or the Associated Property of hazardous
         substances or solid wastes disposed of or otherwise released)
         resulting from or in connection with the ownership, construction,
         occupancy, operation, use and/or maintenance of the Property or the
         Associated Property, regardless of whether the act, omission, event or
         circumstance constituted a violation of any Applicable Environmental
         Law at the time of its existence or occurrence, and (G) any and all
         claims or proceedings (whether brought by private party or
         governmental agencies) for human health, bodily injury, property
         damage, abatement or remediation, environmental damage, cleanup,
         mitigation, removal, natural resource damage or impairment or any
         other injury or damage resulting from or relating to any hazardous or
         toxic substance, solid waste or contaminated material located upon or
         migrating into, from or through the Property or the Associated
         Property (whether or not the release of such materials was caused by
         Mortgagor, a tenant or subtenant or a prior owner or tenant or
         subtenant on the Property or the Associated Property and whether or
         not the alleged liability is attributable to the use, treatment,
         handling, storage, generation, transportation, removal or disposal of
         such substance, waste or material or the mere presence of such
         substance, waste or material on or under the





                                       10
<PAGE>   12
         Property or the Associated Property), which the Mortgagee may have
         liability with respect to due to the making of the loan or loans
         evidenced by the Note, the granting of this Mortgage, the exercise of
         any rights under the Loan Documents, or otherwise.  Mortgagee shall
         have the right to compromise and adjust any such claims, actions and
         judgments, and in addition to the rights to be indemnified as herein
         provided, all amounts paid in compromise, satisfaction or discharge of
         any such claim, action or judgment, and all court costs, attorneys'
         fees and other expenses of every character expended by Mortgagee
         pursuant to the provisions of this section shall be a demand
         obligation (which obligation Mortgagor hereby expressly promises to
         pay) owing by Mortgagor to Mortgagee.  The "Release Date" as used
         herein shall mean the earlier of the following two dates:  (i) the
         date on which the indebtedness and obligations secured hereby have
         been paid and performed in full and this Mortgage has been released of
         record, or (ii) the date on which the lien of this Mortgage is
         foreclosed or a deed in lieu of such foreclosure is fully effective
         and recorded.  WITHOUT LIMITATION, IT IS THE INTENTION OF MORTGAGOR
         AND MORTGAGOR AGREES THAT THE FOREGOING INDEMNITIES SHALL APPLY TO
         EACH INDEMNIFIED PARTY WITH RESPECT TO CLAIMS, DEMANDS, LIABILITIES,
         LOSSES, DAMAGES, CAUSES OF ACTION, JUDGMENTS, PENALTIES, COSTS AND
         EXPENSES (INCLUDING WITHOUT LIMITATION REASONABLE ATTORNEYS' FEES)
         WHICH IN WHOLE OR IN PART ARE CAUSED BY OR ARISE OUT OF THE NEGLIGENCE
         OF SUCH (AND/OR ANY OTHER) INDEMNIFIED PARTY.  However, such
         indemnities shall not apply to any particular indemnified party (but
         shall apply to the other indemnified parties) to the extent the
         subject of the indemnification is caused by or arises out of the gross
         negligence or willful misconduct of such particular indemnified party.
         The foregoing indemnities shall not terminate upon the Release Date or
         upon the release, foreclosure or other termination of this Mortgage
         but will survive the Release Date, foreclosure of this Mortgage or
         conveyance in lieu of foreclosure, and the repayment of the secured
         indebtedness and the discharge and release of this Mortgage and the
         other documents evidencing and/or securing the secured indebtedness.
         Any amount to be paid hereunder by Mortgagor to Mortgagee shall be a
         demand obligation owing by Mortgagor to Mortgagee and shall be subject
         to and covered by the provisions of Section 2.3 hereof.

                 (l)      Insurance.  Mortgagor will carry insurance as
         provided in the Credit Agreement.  In the event of any loss under any
         insurance policies so carried by Mortgagor, Mortgagee shall have the
         right (but not the obligation) to make proof of loss and collect the
         same, and all amounts so received shall be applied toward costs,
         charges and expenses (including reasonable attorneys' fees), if any,
         incurred in the collection thereof, then to the payment, in the order
         determined by Mortgagee in its own discretion, of the secured
         indebtedness, and any balance remaining shall be subject to the order
         of Mortgagor.  Mortgagee is hereby authorized but not obligated to
         enforce in its name or in the name of Mortgagor payment of any or all
         of said policies or settle or compromise any claim in respect thereof,
         and to collect and make receipts for the proceeds thereof and
         Mortgagee is hereby appointed Mortgagor's agent and attorney-in-fact
         to endorse any check or draft payable to Mortgagor in order to collect
         the proceeds of insurance.  In the event of foreclosure of this
         Mortgage, or other transfer of title to the Property in extinguishment
         in whole or in part of the secured indebtedness, all right, title and
         interest of Mortgagor in and to such policies then in force concerning
         the Property and all proceeds payable thereunder shall thereupon vest
         in the purchaser at such foreclosure or other transferee in the event
         of such other transfer of title.





                                       11
<PAGE>   13
                 (m)      Further Assurances.  Mortgagor will, on request of
         Mortgagee, (i) promptly correct any defect, error or omission which
         may be discovered in the contents of this Mortgage, or in any other
         Loan Document, or in the execution or acknowledgment of this Mortgage
         or any other Loan Document; (ii) execute, acknowledge, deliver and
         record and/or file such further instruments (including, without
         limitation, further mortgages, deeds of trust, security agreements,
         financing statements, continuation statements, and assignments of
         production, accounts, funds, contract rights, general intangibles, and
         proceeds) and do such further acts as may be necessary, desirable or
         proper to carry out more effectively the purposes of this Mortgage and
         the other Loan Documents and to more fully identify and subject to the
         liens and security interests hereof any property intended to be
         covered hereby, including specifically, but without limitation, any
         renewals, additions, substitutions, replacements, or appurtenances to
         the Property; and (iii) execute, acknowledge, deliver, and file and/or
         record any document or instrument (including specifically any
         financing statement) desired by Mortgagee to protect the lien or the
         security interest hereunder against the rights or interests of third
         persons.  Mortgagor shall pay all costs connected with any of the
         foregoing.

                 (n)      Name and Place of Business.  Mortgagor will not cause
         or permit any change to be made in its name, identity, or corporate or
         partnership structure, or its federal employer identification number
         unless Mortgagor shall have notified Mortgagee of such change at least
         thirty (30) days prior to the effective date of such change, and shall
         have first taken all action required by Mortgagee for the purpose of
         further perfecting or protecting the liens and security interests in
         the Property created hereby.  Mortgagor's principal place of business
         and chief executive office, and the place where Mortgagor keeps its
         books and records concerning the Property (including, particularly,
         the records with respect to "Production Proceeds", as defined in
         Section 3.1 hereof, from the Mortgaged Properties) has for the
         preceding four months, been, and will continue to be (unless Mortgagor
         notifies Mortgagee of any change in writing at least thirty (30) days
         prior to the date of such change), the address set forth opposite the
         signature of Mortgagor to this Mortgage.

                 (o)      Not a Foreign Person.  Mortgagor is not a "foreign
         person" within the meaning of the Internal Revenue Code of 1986, as
         amended, (hereinafter called the "Code"), Sections 1445 and 7701 (i.e.
         Mortgagor is not a non-resident alien, foreign corporation, foreign
         partnership, foreign trust or foreign estate as those terms are
         defined in the Code and any regulations promulgated thereunder).

         Section 2.2.  Compliance by Operator.  As to any part of the Mortgaged
Properties which is not a working interest, Mortgagor agrees to take all such
action and to exercise all rights and remedies as are available to Mortgagor to
cause the owner or owners of the working interest in such properties to comply
with the covenants and agreements contained herein; and as to any part of the
Mortgaged Properties which is a working interest but which is operated by a
party other than Mortgagor, Mortgagor agrees to take all such action and to
exercise all rights and remedies as are available to Mortgagor (including, but
not limited to, all rights under any operating agreement) to cause the party
who is the operator of such property to comply with the covenants and
agreements contained herein.





                                       12
<PAGE>   14
         Section 2.3.  Performance on Mortgagor's Behalf.  Mortgagor agrees
that, if Mortgagor fails to perform any act or to take any action which
hereunder Mortgagor is required to perform or take, or to pay any money which
hereunder Mortgagor is required to pay, Mortgagee, in Mortgagor's name or its
own name, may, but shall not be obligated to, perform or cause to be performed
such act or take such action or pay such money, and any expenses so incurred by
Mortgagee and any money so paid by Mortgagee shall be a demand obligation owing
by Mortgagor to Mortgagee (which obligation Mortgagor hereby expressly promises
to pay) and Mortgagee, upon making such payment, shall be subrogated to all of
the rights of the person, corporation or body politic receiving such payment.
Each amount due and owing by Mortgagor to Mortgagee pursuant to this Mortgage
shall bear interest each day, from the date of such expenditure or payment
until paid, at a rate equal to the rate as provided for past due principal
under the Note (provided that, should applicable law provide for a maximum
permissible rate of interest on such amounts, such rate shall not be greater
than such maximum permissible rate); all such amounts, together with such
interest thereon, shall be a part of the secured indebtedness and shall be
secured by this Mortgage.

                                  ARTICLE III.

                Assignment of Production, Accounts, and Proceeds

         Section 3.1.  Assignment of Production.  Mortgagor does hereby
absolutely and unconditionally assign, transfer and set over to Mortgagee all
Production which accrues to Mortgagor's interest in the Mortgaged Properties,
all proceeds of such Production and all Payments in Lieu of Production (herein
collectively referred to as the "Production Proceeds"), together with the
immediate and continuing right to collect and receive such Production Proceeds.
Mortgagor directs and instructs any and all purchasers of any Production to pay
to Mortgagee all of the Production Proceeds accruing to Mortgagor's interest
until such time as such purchasers have been furnished with evidence that all
secured indebtedness has been paid and that this Mortgage has been released.
Mortgagor agrees that no purchasers of the Production shall have any
responsibility for the application of any funds paid to Mortgagee.

         Section 3.2.  Effectuating Payment of Production Proceeds to
Mortgagee.  Independent of the foregoing provisions and authorities herein
granted, Mortgagor agrees to execute and deliver any and all transfer orders,
division orders and other instruments that may be requested by Mortgagee or
that may be required by any purchaser of any Production for the purpose of
effectuating payment of the Production Proceeds to Mortgagee.  If under any
existing sales agreements, other than division orders or transfer orders, any
Production Proceeds are required to be paid by the purchaser to Mortgagor so
that under such existing agreements payment cannot be made of such Production
Proceeds to Mortgagee, Mortgagor's interest in all Production Proceeds under
such sales agreements and in all other Production Proceeds which for any reason
may be paid to Mortgagor shall, when received by Mortgagor, constitute trust
funds in Mortgagor's hands and shall be immediately paid over to Mortgagee.
Without limitation upon any of the foregoing, Mortgagor hereby constitutes and
appoints Mortgagee as Mortgagor's special attorney-in-fact (with full power of
substitution, either generally or for such periods or purposes as Mortgagee may
from time to time prescribe) in the name, place and stead of Mortgagor to do
any and every act and exercise any and every power that Mortgagor might or
could do or exercise personally with respect to all Production and Production
Proceeds (the same having been assigned by Mortgagor to Mortgagee pursuant to
Section 3.1 hereof), expressly inclusive, but not limited to, the right, power
and authority to:





                                       13
<PAGE>   15
                 (a)      Execute and deliver in the name of Mortgagor any and
         all transfer orders, division orders, letters in lieu of transfer
         orders, indemnifications, certificates and other instruments of every
         nature that may be requested or required by any purchaser of
         Production from any of the Mortgaged Properties for the purposes of
         effectuating payment of the Production Proceeds to Mortgagee or which
         Mortgagee may otherwise deem necessary or appropriate to effect the
         intent and purposes of the assignment contained in Section 3.1; and

                 (b)      If under any product sales agreements other than
         division orders or transfer orders, any Production Proceeds are
         required to be paid by the purchaser to Mortgagor so that under such
         existing agreements payment cannot be made of such Production Proceeds
         to Mortgagee, to make, execute and enter into such sales agreements or
         other agreements as are necessary to direct Production Proceeds to be
         payable to Mortgagee;

giving and granting unto said attorney-in-fact full power and authority to do
and perform any and every act and thing whatsoever necessary and requisite to
be done as fully and to all intents and purposes, as Mortgagor might or could
do if personally present; and Mortgagor shall be bound thereby as fully and
effectively as if Mortgagor had personally executed, acknowledged and delivered
any of the foregoing certificates or documents.  The powers and authorities
herein conferred upon Mortgagee may be exercised by Mortgagee through any
person who, at the time of the execution of the particular instrument, is an
officer of Mortgagee.  The power of attorney herein conferred is granted for
valuable consideration and hence is coupled with an interest and is irrevocable
so long as the secured indebtedness, or any part thereof, shall remain unpaid.
All persons dealing with Mortgagee or any substitute shall be fully protected
in treating the powers and authorities conferred by this paragraph as
continuing in full force and effect until advised by Mortgagee that all the
secured indebtedness is fully and finally paid.  Mortgagee may, but shall not
be obligated to, take such action as it deems appropriate in an effort to
collect the Production Proceeds and any reasonable expenses (including
reasonable attorney's fees) so incurred by Mortgagee shall be a demand
obligation of Mortgagor and shall be part of the secured indebtedness, and
shall bear interest each day, from the date of such expenditure or payment
until paid, at the rate described in Section 2.3 hereof.

         Section 3.3.  Change of Purchaser.  To the extent a default has
occurred hereunder and is continuing, should any person now or hereafter
purchasing or taking Production fail to make payment promptly to Mortgagee of
the Production Proceeds, Mortgagee shall, subject to then-existing contractual
prohibitions, have the right to make, or to require Mortgagor to make, a change
of purchaser, and the right to designate or approve the new purchaser, and
Mortgagee shall have no liability or responsibility in connection therewith so
long as ordinary care is used in making such designation.

         Section 3.4.  Application of Production Proceeds.  So long as no
default has occurred hereunder, the Production Proceeds received by Mortgagee
during each calendar month shall on the first business day of the next
succeeding calendar month (or, at the option of Mortgagee, on any earlier date)
be applied by Mortgagee as follows:

                 FIRST, to the payment of all secured indebtedness then due and
         payable, in such manner and order as Mortgagee deems advisable;





                                       14
<PAGE>   16
                 SECOND, to the prepayment of the remainder of the secured
         indebtedness in such manner and order and to such extent as Mortgagee
         deems advisable; and

                 THIRD, the remainder, if any, of the Production Proceeds shall
         be paid over to Mortgagor or to Mortgagor's order or to such other
         parties as may be entitled thereto by law.

         After a default hereunder has occurred, all Production Proceeds from
time to time in the hands of Mortgagee shall be applied by it toward the
payment of all secured indebtedness (principal, interest, attorneys' fees and
other fees and expenses) at such times and in such manner and order and to such
extent as Mortgagee deems advisable.

         Section 3.5.  Release From Liability; Indemnification.  Mortgagee and
its successors and assigns are hereby released and absolved from all liability
for failure to enforce collection of the Production Proceeds and from all other
responsibility in connection therewith, except the responsibility of each to
account to Mortgagor for funds actually received by each.  Mortgagor agrees to
indemnify and hold harmless Mortgagee (for purposes of this paragraph, the term
"Mortgagee" shall include the directors, officers, partners, employees and
agents of Mortgagee and any persons or entities owned or controlled by or
affiliated with Mortgagee) from and against any and all claims, demands,
liabilities, losses, damages (including without limitation consequential
damages), causes of action, judgments, penalties, costs and expenses (including
without limitation reasonable attorneys' fees and expenses) imposed upon,
asserted against or incurred or paid by Mortgagee by reason of the assertion
that Mortgagee received, either before or after payment in full of the secured
indebtedness, funds from the production of oil, gas, other hydrocarbons or
other minerals claimed by third persons (and/or funds attributable to sales of
production which (i) were made at prices in excess of the maximum price
permitted by applicable law or (ii) were otherwise made in violation of laws,
rules, regulations and/or orders governing such sales), and Mortgagee shall
have the right to defend against any such claims or actions, employing
attorneys of its own selection, and if not furnished with indemnity
satisfactory to it, Mortgagee shall have the right to compromise and adjust any
such claims, actions and judgments, and in addition to the rights to be
indemnified as herein provided, all amounts paid by Mortgagee in compromise,
satisfaction or discharge of any such claim, action or judgment, and all court
costs, attorneys' fees and other expenses of every character expended by
Mortgagee pursuant to the provisions of this section shall be a demand
obligation (which obligation Mortgagor hereby expressly promises to pay) owing
by Mortgagor to Mortgagee and shall bear interest, from the date expended until
paid, at the rate described in Section 2.3 hereof.  The foregoing indemnities
shall not terminate upon the Release Date or upon the release, foreclosure or
other termination of this Mortgage but will survive the Release Date,
foreclosure of this Mortgage or conveyance in lieu of foreclosure, and the
repayment of the secured indebtedness and the discharge and release of this
Mortgage and the other documents evidencing and/or securing the secured
indebtedness.  WITHOUT LIMITATION, IT IS THE INTENTION OF MORTGAGOR AND
MORTGAGOR AGREES THAT THE FOREGOING RELEASES AND INDEMNITIES SHALL APPLY TO
EACH INDEMNIFIED PARTY WITH RESPECT TO ALL CLAIMS, DEMANDS, LIABILITIES,
LOSSES, DAMAGES (INCLUDING WITHOUT LIMITATION CONSEQUENTIAL DAMAGES), CAUSES OF
ACTION, JUDGMENTS, PENALTIES, COSTS AND EXPENSES (INCLUDING WITHOUT LIMITATION
REASONABLE ATTORNEYS' FEES AND EXPENSES) WHICH IN WHOLE OR IN PART ARE CAUSED
BY OR ARISE OUT OF THE NEGLIGENCE OF SUCH (AND/OR ANY OTHER) INDEMNIFIED
PARTY.However, such indemnities shall not apply to any particular indemnified
party (but shall apply to the other indemnified





                                       15
<PAGE>   17
parties) to the extent the subject of the indemnification is caused by or
arises out of the gross negligence or willful misconduct of such particular
indemnified party.

         Section 3.6.  Absolute Obligation to Pay Note.  Nothing herein
contained shall detract from or limit the obligation to make prompt payment of
the Note, and any and all other secured indebtedness, at the time and in the
manner provided herein and in the Loan Documents, regardless of whether the
Production and Production Proceeds herein assigned are sufficient to pay same,
and the rights under this Article III shall be cumulative of all other rights
under the Loan Documents.

         Section 3.7      Rights Under Oklahoma Oil and Gas Owners' Lien Act.
Mortgagor hereby grants, sells, assigns and sets over unto Lender during the
term hereof, all of Mortgagor's rights and interests pursuant to the provisions
of the Oil and Gas Owners' Lien Act (OKLA. STAT. tit. 52, Sections 548.1-548.6
(the "Oklahoma Act"), hereby vesting in Lender all of Mortgagor's rights as an
interest owner to the continuing security interest in and lien upon the oil or
gas severed or the proceeds of sale.  Lender may, at its option, file the
verified notice of lien in order to perfect such lien, but shall not be
obligated to make such filing and shall not be held liable to Mortgagor for any
act or omission pursuant to the Oklahoma Act.


                                  ARTICLE IV.

                             Remedies Upon Default

         Section 4.1.  Default.  The term "default" as used in this Mortgage
shall mean the occurrence of an "Event of Default" as defined in the Credit
Agreement.

         Section 4.2.  Acceleration of Secured Indebtedness.  Upon the
occurrence of a default, Mortgagee at any time and from time to time may
without notice to Mortgagor or any other person declare any or all of the
secured indebtedness immediately due and payable and all such secured
indebtedness shall thereupon be immediately due and payable, without
presentment, demand, protest, notice of protest, declaration or notice of
acceleration or intention to accelerate, putting the Mortgagor in default,
dishonor, notice of dishonor or any other notice or declaration of any kind,
all of which are hereby expressly waived by Mortgagor, and the liens evidenced
hereby shall be subject to foreclosure in any manner provided for herein or
provided for by law as Mortgagee may elect. The secured indebtedness may be
(and in certain circumstances shall automatically be) accelerated as provided
in the Credit Agreement.

         Section 4.3.  Pre-Foreclosure Remedies.  Upon the occurrence of a
default, or any event or circumstance which, with the lapse of time or the
giving of notice, or both, would constitute a default hereunder, Mortgagee is
authorized, prior or subsequent to the institution of any foreclosure
proceedings, to enter upon the Property, or any part thereof, and to take
possession of the Property and all books and records relating thereto, and to
exercise without interference from Mortgagor any and all rights which Mortgagor
has with respect to the management, possession, operation, protection or
preservation of the Property.  If necessary to obtain the possession provided
for above, Mortgagee may invoke any and all remedies to dispossess Mortgagor.
All costs, expenses and liabilities of every character incurred by Mortgagee in
managing, operating, maintaining, protecting or preserving the Property shall
constitute a demand obligation (which obligation Mortgagor hereby expressly
promises to pay) owing by Mortgagor to Mortgagee and shall bear interest from
date of expenditure until paid at the rate described in Section 2.3 hereof,





                                       16
<PAGE>   18
all of which shall constitute a portion of the secured indebtedness and shall
be secured by this Mortgage and by any other instrument securing the secured
indebtedness.  In connection with any action taken by Mortgagee pursuant to
this Section 4.3, MORTGAGEE SHALL NOT BE LIABLE FOR ANY LOSS SUSTAINED BY
MORTGAGOR RESULTING FROM ANY ACT OR OMISSION OF MORTGAGEE (INCLUDING
MORTGAGEE'S OWN NEGLIGENCE) IN MANAGING THE PROPERTY UNLESS SUCH LOSS IS CAUSED
BY THE WILLFUL MISCONDUCT AND BAD FAITH OF MORTGAGEE, nor shall Mortgagee be
obligated to perform or discharge any obligation, duty or liability of
Mortgagor arising under any agreement forming a part of the Property or arising
under any Permitted Encumbrance or otherwise arising.  Mortgagor hereby assents
to, ratifies and confirms any and all actions of Mortgagee with respect to the
Property taken under this Section 4.3.

         Section 4.4.  Foreclosure.

         (a)     Upon the occurrence of a default, this Mortgage may be
foreclosed as to the Mortgaged Properties, or any part thereof, in any manner
permitted by applicable law.  Cumulative of the foregoing and the other
provisions of this Section 4.4:

         A POWER OF SALE HAS BEEN GRANTED IN THIS MORTGAGE.  A POWER OF SALE
MAY ALLOW MORTGAGEE TO TAKE THE MORTGAGED PROPERTIES AND SELL THEM WITHOUT
GOING TO COURT IN A FORECLOSURE ACTION UPON DEFAULT BY MORTGAGOR UNDER THIS
MORTGAGE.

         (b)     Upon the occurrence of a default, Mortgagee may exercise its
rights of enforcement with respect to the Collateral under the Uniform
Commercial Code or any other statute in force in any state to the extent the
same is applicable law.  Cumulative of the foregoing and the other provisions
of this Section 4.4:

                 (i)      Mortgagee may enter upon the Mortgaged Properties or
         otherwise upon Mortgagor's premises to take possession of, assemble
         and collect the Collateral or to render it unusable; and

                 (ii)     Mortgagee may require Mortgagor to assemble the
         Collateral and make it available at a place Mortgagee designates which
         is mutually convenient to allow Mortgagee to take possession or
         dispose of the Collateral; and

                 (iii)    written notice mailed to Mortgagor as provided herein
         at least ten (10) days prior to the date of public sale of the
         Collateral or prior to the date after which private sale of the
         Collateral will be made shall constitute reasonable notice; and

                 (iv)     in the event of a foreclosure of the liens and/or
         security interests evidenced hereby, the Collateral, or any part
         thereof, and the Mortgaged Properties, or any part thereof, may, at
         the option of Mortgagee, be sold, as a whole or in parts, together or
         separately (including, without limitation, where a portion of the
         Mortgaged Properties is sold, the Collateral related thereto may be
         sold in connection therewith); and

                 (v)      the expenses of sale provided for in clause FIRST of
         Section 4.6 shall include the reasonable expenses of retaking the
         Collateral, or any part thereof, holding the same and preparing the
         same for sale or other disposition; and

                 (vi)     should, under this subsection, the Collateral be
         disposed of other than by sale, any proceeds of such disposition shall
         be treated under Section 4.6 as if the same were sales proceeds;





                                       17
<PAGE>   19
         (c)     To the extent permitted by applicable law, the sale hereunder
of less than the whole of the Property shall not exhaust the powers of sale
herein granted or the right to judicial foreclosure, and successive sale or
sales may be made until the whole of the Property shall be sold and, if the
proceeds of such sale of less than the whole of the Property shall be less than
the aggregate of the indebtedness secured hereby and the expense of conducting
such sale, this Mortgage and the liens and security interests hereof shall
remain in full force and effect as to the unsold portion of the Property just
as though no sale had been made; provided, however, that Mortgagor shall never
have any right to require the sale of less than the whole of the Property.  In
the event any sale hereunder is not completed or is defective in the opinion of
Mortgagee, such sale shall not exhaust the powers of sale hereunder or the
right to judicial foreclosure, and Mortgagee shall have the right to cause a
subsequent sale or sales to be made.  Any sale may be adjourned by announcement
at the time and place appointed for such sale without further notice except as
may be required by law.  Mortgagee acting under power of sale may appoint or
delegate any one or more persons as agent to perform any act or acts necessary
or incident to any sale held by it (including, without limitation, the posting
of notices and the conduct of sale), and such appointment need not be in
writing or recorded.  Any and all statements of fact or other recitals made in
any deed or deeds, or other instruments of transfer, given in connection with a
sale as to nonpayment of the secured indebtedness or as to the occurrence of
any default, or as to all of the secured indebtedness having been declared to
be due and payable, or as to the request to sell, or as to notice of time,
place and terms of sale and the properties to be sold having been duly given,
or as to any other act or thing having been duly done, shall be taken as prima
facie evidence of the truth of the facts so stated and recited.  With respect
to any sale held in foreclosure of the liens and/or security interests covered
hereby, it shall not be necessary for the Mortgagee, any public officer acting
under execution or order of the court or any other party to have physically
present or constructively in his/her or its possession, either at the time of
or prior to such sale, the Property or any part thereof.

         Section 4.5.   As to Other Mortgaged Properties located in the State
of Oklahoma, Mortgagor hereby confers on Lender the power to sell the Mortgaged
Properties in accordance with the Oklahoma Power of Sale Mortgage Foreclosure
Act (OKLA. STAT. tit. 46, Sections 41-49), as the same may be amended from time
to time.  Mortgagor hereby represents and warrants that this Mortgage
transaction does not involve a consumer loan as said term is defined in Section
3-104 of Title 14A of the Oklahoma Statutes, that this Mortgage does not secure
an extension of credit made primarily for agricultural purposes as defined in
paragraph 4 of Section 1-301 of Title 14A of the Oklahoma Statutes, and that
this Mortgage is not a mortgage on the Mortgagor's homestead.

         Section 4.6.  Receiver.  In addition to all other remedies herein
provided for, Mortgagor agrees that, upon the occurrence of a default or any
event or circumstance which, with the lapse of time or the giving of notice, or
both, would constitute a default hereunder, Mortgagee shall as a matter of
right be entitled to the appointment of a receiver or receivers for all or any
part of the Property, whether such receivership be incident to a proposed sale
(or sales) of such property or otherwise, and without regard to the value of
the Property or the solvency of any person or persons liable for the payment of
the indebtedness secured hereby, and Mortgagor does hereby consent to the
appointment of such receiver or receivers, waives any and all defenses to such
appointment, and agrees not to oppose any application therefor by Mortgagee,
and agrees that such appointment shall in no manner impair, prejudice or
otherwise affect the rights of Mortgagee under Article III hereof.  Mortgagor
expressly waives notice of a hearing for





                                       18
<PAGE>   20
appointment of a receiver and the necessity for bond or an accounting by the
receiver.  Nothing herein is to be construed to deprive Mortgagee of any other
right, remedy or privilege it may now or hereafter have under the law to have a
receiver appointed.  Any money advanced by Mortgagee in connection with any
such receivership shall be a demand obligation (which obligation Mortgagor
hereby expressly promises to pay) owing by Mortgagor to Mortgagee and shall
bear interest, from the date of making such advancement by Mortgagee until
paid, at the rate described in Section 2.3 hereof.

         Section 4.7.  Proceeds of Foreclosure.  The proceeds of any sale held
in foreclosure of the liens and/or security interests evidenced hereby shall be
applied:

                 FIRST, to the payment of all necessary costs and expenses
         incident to such foreclosure sale, including but not limited to all
         court costs and charges of every character in the event foreclosed by
         suit;

                 SECOND, to the payment of the secured indebtedness in such
         manner and order as Mortgagee may elect; and

                 THIRD, the remainder, if any there shall be, shall be paid to
         Mortgagor, or to Mortgagor's heirs, devisees, representatives,
         successors or assigns, or such other persons as may be entitled
         thereto by law.

         Section 4.8.  Mortgagee as Purchaser.  Any party constituting
Mortgagee shall have the right to become the purchaser at any sale held in
foreclosure of the liens and/or security interests evidenced hereby, and any
party constituting Mortgagee which is purchasing at any such sale shall have
the right to credit upon the amount of the bid made therefor, to the extent
necessary to satisfy such bid, the secured indebtedness owing to such party, or
if such party holds less than all of such indebtedness, the pro rata part
thereof owing to such party, accounting to all other parties constituting
Mortgagee who are not joining in such bid in cash for the portion of such bid
or bids apportionable to such non-bidding parties.

         Section 4.9.  Foreclosure as to Matured Debt.  Upon the occurrence of
a default, Mortgagee shall have the right to proceed with foreclosure of the
liens and/or security interests evidenced hereby without declaring the entire
secured indebtedness due, and in such event, any such foreclosure sale may be
made subject to the unmatured part of the secured indebtedness and shall not in
any manner affect the unmatured part of the secured indebtedness, but as to
such unmatured part, this Mortgage shall remain in full force and effect just
as though no sale had been made.  The proceeds of such sale shall be applied as
provided in Section 4.6 except that the amount paid under clause SECOND thereof
shall be only the matured portion of the secured indebtedness and any proceeds
of such sale in excess of those provided for in clauses FIRST and SECOND
(modified as provided above) shall be applied as provided in clause SECOND and
THIRD of Section 3.4 hereof.  Several sales may be made hereunder without
exhausting the right of sale for any unmatured part of the secured
indebtedness.

         Section 4.10.  Remedies Cumulative.  All remedies herein provided for
are cumulative of each other and of all other remedies existing at law or in
equity and are cumulative of any and all other remedies provided for in any
other Loan Document, and, in addition to the remedies herein provided, there
shall continue to be available all such other remedies as may now or hereafter
exist at law or in equity for the collection of the secured indebtedness and
the enforcement of the covenants herein and the foreclosure of the liens and/or
security interests evidenced hereby, and the





                                       19
<PAGE>   21
resort to any remedy provided for hereunder or under any such other Loan
Document or provided for by law shall not prevent the concurrent or subsequent
employment of any other appropriate remedy or remedies.

         Section 4.11.  Discretion as to Security.  Mortgagee may resort to any
security given by this Mortgage or to any other security now existing or
hereafter given to secure the payment of the secured indebtedness, in whole or
in part, and in such portions and in such order as may seem best to Mortgagee
in its sole and uncontrolled discretion, and any such action shall not in any
way be considered as a waiver of any of the rights, benefits, liens or security
interests evidenced by this Mortgage.

         Section 4.12.  Mortgagor's Waiver of Certain Rights.  To the full
extent Mortgagor may do so, Mortgagor agrees that Mortgagor will not at any
time insist upon, plead, claim or take the benefit or advantage of any law now
or hereafter in force providing for any appraisement, valuation, stay,
extension or redemption, and Mortgagor, for Mortgagor, Mortgagor's heirs,
devisees, representatives, successors and assigns, and for any and all persons
ever claiming any interest in the Property, to the extent permitted by
applicable law, hereby waives and releases all rights of appraisement,
valuation, stay of execution, redemption, notice of intention to mature or
declare due the whole of the secured indebtedness, notice of election to mature
or declare due the whole of the secured indebtedness and all rights to a
marshaling of assets of Mortgagor, including the Property, or to a sale in
inverse order of alienation in the event of foreclosure of the liens and/or
security interests hereby created.  Mortgagor shall not have or assert any
right under any statute or rule of law pertaining to the marshaling of assets,
sale in inverse order of alienation, the exemption of homestead, the
administration of estates of decedents, or other matters whatever to defeat,
reduce or affect the right under the terms of this Mortgage to a sale of the
Property for the collection of the secured indebtedness without any prior or
different resort for collection, or the right under the terms of this Mortgage
to the payment of the secured indebtedness out of the proceeds of sale of the
Property in preference to every other claimant whatever.  If any law referred
to in this section and now in force, of which Mortgagor or Mortgagor's heirs,
devisees, representatives, successors or assigns or any other persons claiming
any interest in the Mortgaged Properties or the Collateral might take advantage
despite this section, shall hereafter be repealed or cease to be in force, such
law shall not thereafter be deemed to preclude the application of this section.

         Section 4.13.  Mortgagor as Tenant Post-Foreclosure.  In the event
there is a foreclosure sale hereunder and at the time of such sale Mortgagor or
Mortgagor's heirs, devisees, representatives, successors or assigns or any
other persons claiming any interest in the Property by, through or under
Mortgagor are occupying or using the Property, or any part thereof, each and
all shall immediately become the tenant of the purchaser at such sale, which
tenancy shall be a tenancy from day to day, terminable at the will of either
landlord or tenant, at a reasonable rental per day based upon the value of the
property occupied, such rental to be due daily to the purchaser.  To the extent
permitted by applicable law, the purchaser at such sale shall, notwithstanding
any language herein apparently to the contrary, have the sole option to demand
immediate possession following the sale or to permit the occupants to remain as
tenants at will.  In the event the tenant fails to surrender possession of said
property upon demand, the purchaser shall be entitled to institute and maintain
a summary action for possession of the property (such as an action for forcible
entry and detainer) in any court having jurisdiction.





                                       20
<PAGE>   22
         Section 4.14.  Waiver of Oklahoma Appraisement.  As to Property
situated in or otherwise subject to the laws of the State of Oklahoma,
appraisement of the Property is hereby waived (or not) at the option of Lender,
such option to be exercised at the time judgment is rendered in any foreclosure
hereof or at any time prior thereto.


                                   ARTICLE V.

                                 Miscellaneous

         Section 5.1.  Scope of Mortgage.  This Mortgage is a mortgage of both
real/immovable and personal/movable property, a security agreement, a financing
statement and an assignment, and also covers proceeds and fixtures.

         Section 5.2.  Effective as a Financing Statement.  This Mortgage
covers goods which are or are to become fixtures on the real property described
herein, and this Mortgage shall be effective as a financing statement filed as
a fixture filing with respect to all fixtures included within the Property.
This Mortgage shall also be effective as a financing statement, filed as a
fixture filing, covering minerals and other substances of value which may be
extracted from the earth (including without limitation oil and gas), and
accounts related thereto, which will be financed at the wellhead or minehead of
the wells or mines located on the Mortgaged Properties.  This Mortgage is to be
filed for record in the real/immovable property records of each county where
any part of the Mortgaged Properties is situated or which lies shoreward of any
Mortgaged Property (i.e., to the extent a Mortgaged Property lies offshore
within the projected seaward extension of the relevant county boundaries), and
may also be filed in the offices of the Bureau of Land Management or the
Minerals Management Service or any relevant state agency (or any successor
agencies).  This Mortgage shall also be effective as a financing statement
covering any other Property and may be filed in any other appropriate filing or
recording office.  The mailing address of Mortgagor is the address of Mortgagor
set forth at the end of this Mortgage and the address of Mortgagee from which
information concerning the security interests hereunder may be obtained is the
address of Mortgagee set forth at the end of this Mortgage.

         Section 5.3.  Reproduction of Mortgage as Financing Statement.  A
carbon, photographic, facsimile or other reproduction of this Mortgage or of
any financing statement relating to this Mortgage shall be sufficient as a
financing statement for any of the purposes referred to in Section 5.2.

         Section 5.4.  Notice to Account Debtors.  In addition to, but without
limitation of, the rights granted in Article III hereof, Mortgagee may, at any
time after a default has occurred that is continuing, notify the account
debtors or obligors of any accounts, chattel paper, negotiable instruments or
other evidences of indebtedness included in the Collateral to pay Mortgagee
directly.

         Section 5.5.  Waivers.  Mortgagee may at any time and from time to
time in writing waive compliance by Mortgagor with any covenant herein made by
Mortgagor to the extent and in the manner specified in such writing, or consent
to Mortgagor's doing any act which hereunder Mortgagor is prohibited from
doing, or to Mortgagor's failing to do any act which hereunder Mortgagor is
required to do, to the extent and in the manner specified in such writing, or
release any part of the Property or any interest therein or any Production
Proceeds from the lien and security interest of this Mortgage.  Any party
liable, either directly or indirectly, for the secured indebtedness or for any
covenant herein or in any other Loan Document may be released from all or any
part





                                       21
<PAGE>   23
of such obligations without impairing or releasing the liability of any other
party.  No such act shall in any way impair any rights or powers hereunder
except to the extent specifically agreed to in such writing.

         Section 5.6.  No Impairment of Security.  The lien, security interest
and other security rights hereunder shall not be impaired by any indulgence,
moratorium or release which may be granted including, but not limited to, any
renewal, extension or modification which may be granted with respect to any
secured indebtedness, or any surrender, compromise, release, renewal,
extension, exchange or substitution which may be granted in respect of the
Property (including without limitation Production Proceeds), or any part
thereof or any interest therein, or any release or indulgence granted to any
endorser, guarantor or surety of any secured indebtedness.

         Section 5.7.  Acts Not Constituting Waiver.  Any default may be waived
without waiving any other prior or subsequent default.  Any default may be
remedied without waiving the default remedied.  Neither failure to exercise,
nor delay in exercising, any right, power or remedy upon any default shall be
construed as a waiver of such default or as a waiver of the right to exercise
any such right, power or remedy at a later date.  No single or partial exercise
of any right, power or remedy hereunder shall exhaust the same or shall
preclude any other or further exercise thereof, and every such right, power or
remedy hereunder may be exercised at any time and from time to time.  No
modification or waiver of any provision hereof nor consent to any departure by
Mortgagor therefrom shall in any event be effective unless the same shall be in
writing and signed by Mortgagee and then such waiver or consent shall be
effective only in the specific instances, for the purpose for which given and
to the extent therein specified.  No notice to nor demand on Mortgagor in any
case shall of itself entitle Mortgagor to any other or further notice or demand
in similar or other circumstances.  Acceptance of any payment in an amount less
than the amount then due on any secured indebtedness shall be deemed an
acceptance on account only and shall not in any way excuse the existence of a
default hereunder.

         Section 5.8.  Mortgagor's Successors.  In the event the ownership of
the Property or any part thereof becomes vested in a person other than
Mortgagor, then, without notice to Mortgagor, such successor or successors in
interest may be dealt with, with reference to this Mortgage and to the
indebtedness secured hereby, in the same manner as with Mortgagor, without in
any way vitiating or discharging Mortgagor's liability hereunder or for the
payment of the indebtedness or performance of the obligations secured hereby.
No transfer of the Property, no forbearance, and no extension of the time for
the payment of the indebtedness secured hereby, shall operate to release,
discharge, modify, change or affect, in whole or in part, the liability of
Mortgagor hereunder or for the payment of the indebtedness or performance of
the obligations secured hereby or the liability of any other person hereunder
or for the payment of the indebtedness secured hereby.

         Section 5.9.  Place of Payment.  All secured indebtedness which may be
owing hereunder at any time by Mortgagor shall be payable at the place
designated in the Credit Agreement (or if no such designation is made, at the
address of Mortgagee indicated at the end of this Mortgage), or at such other
place as Mortgagee may designate in writing.

         Section 5.10.  Subrogation to Existing Liens.  To the extent that
proceeds of the  secured indebtedness are used to pay indebtedness secured by
any outstanding lien, security interest, charge or prior encumbrance against
the Property, such proceeds have been advanced at Mortgagor's request, and the
party or parties





                                       22
<PAGE>   24
advancing the same shall be subrogated to any and all rights, security
interests and liens owned by any owner or holder of such outstanding liens,
security interests, charges or encumbrances, irrespective of whether said
liens, security interests, charges or encumbrances are released, and it is
expressly understood that, in consideration of the payment of such
indebtedness, Mortgagor hereby waives and releases all demands and causes of
action for offsets and payments to, upon and in connection with the said
indebtedness.

         Section 5.11.  Application of Payments to Certain Indebtedness.  If
any part of the secured indebtedness cannot be lawfully secured by this
Mortgage or if any part of the Property cannot be lawfully subject to the lien
and security interest hereof to the full extent of such indebtedness, then all
payments made shall be applied on said indebtedness first in discharge of that
portion thereof which is not secured by this Mortgage.

         Section 5.12.  Compliance With Usury Laws.  It is the intent of
Mortgagor, Mortgagee and all other parties to the Loan Documents to contract in
strict compliance with applicable usury law from time to time in effect.  In
furtherance thereof, it is stipulated and agreed that none of the terms and
provisions contained herein shall ever be construed to create a contract to
pay, for the use, forbearance or detention of money, interest in excess of the
maximum amount of interest permitted to be charged by applicable law from time
to time in effect.

         Section 5.13.  Release of Mortgage.  If all of the secured
indebtedness be paid as the same becomes due and payable and all of the
covenants, warranties, undertakings and agreements made in this Mortgage are
kept and performed and no further obligation shall exist to provide credit or
advance funds to Mortgagor or the maker of any promissory note (or other
obligor with respect to other indebtedness) secured hereby, then, at
Mortgagor's request, this Mortgage shall be released, in due form and at
Mortgagor's cost; provided, however, that, notwithstanding such release,
certain indemnifications, and other rights, which are provided herein to
continue following the release hereof shall continue in effect unaffected by
such release; and provided further that if any payment to Mortgagee is held to
constitute a preference or a voidable transfer under applicable state or
federal laws or if for any other reason Mortgagee is required to refund such
payment to the payor thereof or to pay the amount thereof to any third party,
this Mortgage shall be reinstated to the extent of such payment or payments.

         Section 5.14.  Notices.  All notices, requests, consents, demands and
other communications required or permitted hereunder shall be in writing and
shall be deemed sufficiently given or furnished if delivered by personal
delivery, by telecopy, by delivery service with proof of delivery, or by
registered or certified United States mail, postage prepaid, at the addresses
specified at the end of this Mortgage (unless changed by similar notice in
writing given by the particular party whose address is to be changed).  Any
such notice or communication shall be deemed to have been given (a) in the case
of personal delivery or delivery service, as of the date of first attempted
delivery at the address and in the manner provided herein, (b) in the case of
telecopy, upon receipt, and (c) in the case of registered or certified United
States mail, three days after deposit in the mail.  Notwithstanding the
foregoing, or anything else in the Loan Documents which may appear to the
contrary, any notice given in connection with a foreclosure of the liens and/or
security interests created hereunder, or otherwise in connection with the
exercise by Mortgagee of its rights hereunder or under any other Loan Document,
which is given in a manner permitted by applicable law shall constitute proper
notice; without limitation of the foregoing, notice given in a form required or
permitted by statute shall (as to the portion of the Property to which such
statute is applicable) constitute proper notice.





                                       23
<PAGE>   25
         Section 5.15.  Invalidity of Certain Provisions.  A determination that
any provision of this Mortgage is unenforceable or invalid shall not affect the
enforceability or validity of any other provision and the determination that
the application of any provision of this Mortgage to any person or circumstance
is illegal or unenforceable shall not affect the enforceability or validity of
such provision as it may apply to other persons or circumstances.

         Section 5.16.  Gender; Titles.  Within this Mortgage, words of any
gender shall be held and construed to include any other gender, and words in
the singular number shall be held and construed to include the plural, unless
the context otherwise requires.  Titles appearing at the beginning of any
subdivisions hereof are for convenience only, do not constitute any part of
such subdivisions, and shall be disregarded in construing the language
contained in such subdivisions.

         Section 5.17.  Recording.  Mortgagor will cause this Mortgage and all
amendments and supplements thereto and substitutions therefor and all financing
statements and continuation statements relating thereto to be recorded, filed,
re-recorded and refiled in such manner and in such places as Mortgagee shall
reasonably request and will pay all such recording, filing, re-recording and
refiling taxes, fees and other charges.

         Section 5.18.  Reporting Compliance.  Mortgagor agrees to comply with
any and all reporting requirements applicable to the transaction evidenced by
the Note and secured by this Mortgage which are set forth in any law, statute,
ordinance, rule, regulation, order or determination of any governmental
authority, and further agrees upon request of Mortgagee to furnish Mortgagee
with evidence of such compliance.

         Section 5.19.  Certain Consents.  Except where otherwise expressly
provided herein, in any instance hereunder where the approval, consent or the
exercise of judgment of Mortgagee is required, the granting or denial of such
approval or consent and the exercise of such judgment shall be within the sole
discretion of Mortgagee, and Mortgagee shall not, for any reason or to any
extent, be required to grant such approval or consent or exercise such judgment
in any particular manner, regardless of the reasonableness of either the
request or Mortgagee's judgment.

         Section 5.20.  Certain Obligations of Mortgagor.  Without limiting
Mortgagor's obligations hereunder, Mortgagor's liability hereunder shall extend
to and include all post petition interest, expenses, and other duties and
liabilities with respect to Mortgagor's obligations hereunder which would be
owed but for the fact that the same may be unenforceable due to the existence
of a bankruptcy, reorganization or similar proceeding.

         Section 5.21.  Agent and Lenders.  On the date hereof, ING is both the
"Agent" under the Credit Agreement and the only Lender thereunder.  It is
hereby contemplated that additional persons shall or may hereafter become
Lenders under the Credit Agreement, and in such event: (a) all references
herein to indebtedness, obligations, or promissory notes owing to Mortgagee
shall refer to indebtedness, obligations, or promissory notes owing to any
person included within the definition of Lenders, as used in the Credit
Agreement, and (b) in its capacity as Agent under the Credit Agreement, ING
together with its successors in such capacity, shall have all authority,
without the need to secure the consent or joinder of any other parties
constituting Lenders under the Credit Agreement, to perform any acts and/or
enforce any remedies afforded Mortgagee hereunder, including without limitation
any remedies





                                       24
<PAGE>   26
afforded Mortgagee under Article IV hereof, and to receive any notices or
payments (including without limitation payment of Production Proceeds pursuant
to Article III hereof), on behalf of the parties constituting Lenders under the
Credit Agreement, and (c) any rights, titles, liens and security interests in
or relating to the Property shall be automatically held, upon and subject to
the terms of the Credit Agreement, by ING, as Agent, for the benefit of all
parties constituting Lenders under the Credit Agreement, and any rights and
remedies afforded Mortgagee hereunder (including without limitation any of same
relating to indemnities) shall be automatically held and exercised, upon and
subject to the terms of the Credit Agreement, by ING as Agent for all parties
constituting Lenders under the Credit Agreement.

         Section 5.22.  Counterparts.  This Mortgage may be executed in several
counterparts, all of which are identical, except that, to facilitate
recordation, certain counterparts hereof may include only those portions of the
Exhibits hereto which contain descriptions of the properties located in (or
otherwise subject to the recording or filing requirements and/or protections of
the recording or filing acts or regulations of) the recording jurisdiction in
which the particular counterpart is to be recorded, and other portions of such
Exhibits shall be included in such counterparts by reference only.  All of such
counterparts together shall constitute one and the same instrument.  Complete
copies of this Mortgage containing the entirety of the Exhibits hereto  have
been retained by Mortgagor and Mortgagee.

         Section 5.23.  Successors and Assigns.  The terms, provisions,
covenants, representations, indemnifications and conditions hereof shall be
binding upon Mortgagor, and the successors and assigns of Mortgagor, and shall
inure to the benefit of Mortgagee and the successors and assigns of Mortgagee,
and shall constitute covenants running with the Mortgaged Properties.  All
references in this Mortgage to Mortgagor or Mortgagee shall be deemed to
include all such successors and assigns.

         SECTION 5.24.  FINAL AGREEMENT OF THE PARTIES.  THE WRITTEN LOAN
DOCUMENTS REPRESENT THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE
CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL
AGREEMENTS OF THE PARTIES.  THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE
PARTIES.

         SECTION 5.25.  CHOICE OF LAW.  WITHOUT REGARD TO PRINCIPLES OF
CONFLICTS OF LAW, THIS MORTGAGE SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE
WITH AND GOVERNED BY THE LAWS OF THE STATE OF NEW YORK APPLICABLE TO CONTRACTS
MADE AND TO BE PERFORMED ENTIRELY WITHIN SUCH STATE AND THE LAWS OF THE UNITED
STATES OF AMERICA, EXCEPT THAT TO THE EXTENT THAT THE LAW OF A STATE IN WHICH A
PORTION OF THE PROPERTY IS LOCATED (OR WHICH IS OTHERWISE APPLICABLE TO A
PORTION OF THE PROPERTY) NECESSARILY OR, IN THE SOLE DISCRETION OF MORTGAGEE,
APPROPRIATELY GOVERNS WITH RESPECT TO PROCEDURAL AND SUBSTANTIVE MATTERS
RELATING TO THE CREATION, PERFECTION AND ENFORCEMENT OF THE LIENS, SECURITY
INTERESTS AND OTHER RIGHTS AND REMEDIES OF THE MORTGAGEE GRANTED HEREIN, THE
LAW OF SUCH STATE SHALL APPLY AS TO THAT PORTION OF THE PROPERTY LOCATED IN (OR
WHICH IS OTHERWISE SUBJECT TO THE LAWS OF) SUCH STATE.





                                       25
<PAGE>   27
         IN WITNESS WHEREOF, this instrument is executed by Mortgagor this 15th
day of  May, 1998.

                                   MORTGAGOR:

                                   PERFORMANCE PETROLEUM CO.


                                   By: /s/ BRUCE D. BENSON
                                       ---------------------------------------
                                       Bruce D. Benson
                                       President and Chief Executive Officer


                                   UNITED STATES GAS GATHERING CO., INC.


                                   By: /s/ BRUCE D. BENSON
                                       ---------------------------------------
                                       Bruce D. Benson
                                       President and Chief Executive Officer


                                   PACIFIC OSAGE, INC.


                                   By: /s/ BRUCE D. BENSON
                                       ---------------------------------------
                                       Bruce D. Benson
                                       President and Chief Executive Officer


The address of Mortgagee is:           The address of Mortgagor is:

135 E. 57th Street                     1560 Broadway, Suite 1900
New York, New York 10022               Denver, Colorado  80202





                                       26
<PAGE>   28
                                ACKNOWLEDGMENTS

STATE OF TEXAS            )
                          )
COUNTY OF TARRANT         )


         The foregoing instrument was acknowledged before me on this 15th day
of May, 1998, by Bruce D. Benson, President and Chief Executive Officer of
Performance Petroleum Co., a Colorado corporation, on behalf of such
corporation.

                                                       /s/
                                        -------------------------------------
                                        NOTARY PUBLIC, State of Texas        

         [SEAL]




STATE OF TEXAS            )
                          )
COUNTY OF TARRANT         )


         The foregoing instrument was acknowledged before me on this 15th day
of May, 1998, by Bruce D. Benson, President and Chief Executive Officer of
United States Gas Gathering Co., Inc., a Delaware corporation, on behalf of
such corporation.


                                                       /s/
                                        -------------------------------------
                                        NOTARY PUBLIC, State of Texas        

         [SEAL]



STATE OF TEXAS            )
                          )
COUNTY OF TARRANT         )


         The foregoing instrument was acknowledged before me on this 15th day
of May, 1998, by Bruce D. Benson, President and Chief Executive Officer of
Pacific Osage, Inc., an Oklahoma corporation, on behalf of such corporation.


                                                       /s/     
                                        -------------------------------------
                                        NOTARY PUBLIC, State of Texas        

         [SEAL]





                                       27