<PAGE>
                                                                    EXHIBIT 10.2

                                                        FINAL EXECUTION VERSION]

================================================================================




                              SUBSIDIARY GUARANTEE



                                     made by


                             each of the Guarantors
                         from time to time party hereto


                                   in favor of


                              the Several Creditors
                  from time to time party to the Loan Documents


                                       and


                              JPMORGAN CHASE BANK,
                             as Administrative Agent



                          Dated as of December 17, 2002



================================================================================


<PAGE>

                                TABLE OF CONTENTS

<Table>
<S>                                                                                                              <C>
SECTION 1 DEFINITIONS.............................................................................................2
   1.1      Defined Terms.........................................................................................2
SECTION 2 GUARANTEE...............................................................................................3
   2.1      Guarantee.............................................................................................3
   2.2      Right of Contribution.................................................................................4
   2.3      Right of Set-off......................................................................................4
   2.4      No Subrogation........................................................................................4
   2.5      Amendments, etc. with respect to the Obligations; Waiver of Rights....................................5
   2.6      Guarantee Absolute and Unconditional..................................................................5
   2.7      Reinstatement.........................................................................................6
   2.8      Payments..............................................................................................6
SECTION 3 REPRESENTATIONS AND WARRANTIES..........................................................................6
   3.1      Representations and Warranties........................................................................6
SECTION 4 COVENANTS...............................................................................................7
   4.1      Covenants.............................................................................................7
   4.2      Authority of Administrative Agent.....................................................................7
   4.3      Subordination of Indebtedness.........................................................................7
SECTION 5 MISCELLANEOUS...........................................................................................9
   5.1      Notices...............................................................................................9
   5.2      Counterparts..........................................................................................9
   5.3      Severability..........................................................................................9
   5.4      Integration...........................................................................................9
   5.5      Amendments in Writing; No Waiver; Cumulative Remedies.................................................9
   5.6      Loan Documents.......................................................................................10
   5.7      Section Headings.....................................................................................10
   5.8      Successors and Assigns...............................................................................10
   5.9      GOVERNING LAW........................................................................................10
   5.10     Submission to Jurisdiction; Waivers..................................................................10
   5.11     Acknowledgments......................................................................................11
   5.12     WAIVERS OF JURY TRIAL................................................................................11
   5.13     Additional Obligors..................................................................................11
   5.14     Release..............................................................................................11
</Table>

SCHEDULES
Schedule 1        Address for Notices
Schedule 2        Form of Assumption Agreement




                                        i

<PAGE>


                              SUBSIDIARY GUARANTEE

         SUBSIDIARY GUARANTEE, dated as of December 17, 2002, is made by each of
the entities that is a signatory hereto (each of the signatories hereto,
together with any other Restricted Subsidiary of the Borrower that becomes a
party hereto from time to time after the date hereof, the "Guarantors"), in
favor of JPMORGAN CHASE BANK, as administrative agent (in such capacity, the
"Administrative Agent") for the lenders (the "Lenders") parties to the Credit
Agreement and all other Creditors.

                                    RECITALS

         A. The Lenders have severally agreed to make Loans to and to
participate in Letters of Credit issued for the account of the Borrower upon the
terms and subject to the conditions set forth in the Credit Agreement dated as
of even date herewith (as such may be amended, supplemented or otherwise
modified from time to time, the "Credit Agreement"), among WESTPORT RESOURCES
CORPORATION, a Nevada corporation (the "Borrower"), the Lenders, the Syndication
Agent, the Documentation Agents and the Administrative Agent.

         B. Certain Creditors have entered, and may, in the future, enter into
one or more Interest Rate Protection Agreements, Commodity Price Risk Management
Agreements, foreign currency exchange agreements, commodity price protection
agreements or other interest or currency exchange rate or commodity price
hedging arrangements with the Borrower or any Guarantor (such agreements or
arrangements, while such Creditor or its Affiliate is a party to the Credit
Agreement, being "Hedging Agreements").

         C. The Borrower owns directly or indirectly all of the issued and
outstanding Capital Stock of each Guarantor.

         D. The proceeds of the Loans, Letters of Credit and the Hedging
Agreements will be used in part to enable the Borrower to make valuable
transfers to each Guarantor in connection with the operation of its business.

         E. The Borrower and the Guarantors are engaged in related businesses,
and each Guarantor will derive substantial direct and indirect benefit from the
making of the Loans, the issuance of the Letters of Credit and the execution of
the Hedging Agreements.

         F. The Loans, the Letters of Credit and Hedging Agreements are
necessary and convenient to the conduct, promotion and attainment of the
business of the Borrower and the Guarantors.

         G. To induce the Lenders to enter the Credit Agreement and to make the
Loans and participate in the Letters of Credit issued thereunder and to induce
the Creditors to enter into Hedging Agreements, the Guarantors have agreed to
guarantee the obligations of the Borrower under the Credit Agreement and of the
Loan Parties under the Hedging Agreements.

         H. Now, therefore, in consideration of the premises, the Guarantors
hereby agree with the Administrative Agent and the Creditors, as follows:




<PAGE>

                                    SECTION 1
                                   DEFINITIONS

         1.1 Defined Terms.

                  (a) Unless otherwise defined herein, each term defined in the
Credit Agreement and used herein shall have the meaning given to it in the
Credit Agreement.

                  (b) As used herein, "Creditor" means the Agents, any Lender or
any Affiliate of a Lender party to any Hedging Agreement with a Loan Party while
such Lender is a party to the Credit Agreement.

                  (c) As used herein, "Obligations" means the collective
reference to the unpaid principal of and interest on the Loans, Letter of Credit
Outstandings and Hedging Agreements (regardless of whether such Hedging
Agreements were executed prior to or after the date hereof) and all other
obligations and liabilities of the Borrower or any other Loan Party (including,
without limitation, interest accruing at the then applicable rate provided in
the Credit Agreement after the maturity of the Loans and interest accruing at
the then applicable rate provided in the Credit Agreement after the filing of
any petition in bankruptcy, or the commencement of any insolvency,
reorganization or like proceeding, relating to the Borrower or any of its
Restricted Subsidiaries whether or not a claim for post-filing or post-petition
interest is allowed in such proceeding) to the Administrative Agent or any
Creditor, whether direct or indirect, absolute or contingent, due or to become
due, or now existing or hereafter incurred, which may arise under, out of, or in
connection with, the Credit Agreement, any Note, this Guarantee, any Hedging
Agreement, any other Loan Document or any other document made, delivered or
given in connection therewith, whether on account of principal, interest,
reimbursement obligations, fees, indemnities, costs, expenses or otherwise
(including, without limitation, all fees and disbursements of counsel to the
Administrative Agent or to the Creditors that are required to be paid by the
Borrower or any Guarantor pursuant to the terms of the Credit Agreement or this
Guarantee or any other Loan Document).

                  (d) As used herein, "Loan Document" means the Credit
Agreement, any Note, the Pledge Agreement, this Guarantee, the L/C Applications,
any Mortgage and any Hedging Agreement with a Creditor.

                  (e) As used herein, "Guarantor Claims" means all debts and
obligations of the Borrower or any other Guarantor to the Borrower or any other
Guarantor, as the case may be, whether such debts and obligations now exist or
are hereafter incurred or arise, or whether the obligation of the debtor thereon
be direct, contingent, primary, secondary, several, joint and several, or
otherwise, and irrespective of whether such debts or obligations be evidenced by
note, contract, open account, or otherwise, and irrespective of the Person or
Persons in whose favor such debts or obligations may, at their inception, have
been, or may hereafter be created, or the manner in which they have been or may
hereafter be acquired by.

                  (f) The words "hereof," "herein" and "hereunder" and words of
similar import when used in this Guarantee shall refer to this Guarantee as a
whole and not to any






                                      -2-
<PAGE>

particular provision of this Guarantee, and section and paragraph references are
to this Guarantee unless otherwise specified.

                  (g) The meanings given to terms defined herein shall be
equally applicable to both the singular and plural forms of such terms.

                                    SECTION 2
                                    GUARANTEE

         2.1 Guarantee.

                  (a) Subject to the provisions of subsection 2.1(b), each of
the Guarantors hereby, jointly and severally, unconditionally and irrevocably,
guarantees to the Administrative Agent and the Creditors and their respective
successors, indorsees, transferees and assigns, the prompt and complete payment
and performance by the Borrower when due (whether at the stated maturity, by
acceleration or otherwise) of the Obligations.

                  (b) Anything herein or in any other Loan Document to the
contrary notwithstanding, the maximum liability of each Guarantor hereunder and
under the other Loan Documents shall in no event exceed the amount which can be
guaranteed by such Guarantor under applicable federal and state laws relating to
the insolvency of debtors.

                  (c) Each Guarantor further agrees to pay any and all expenses
(including, without limitation, all reasonable fees and disbursements of
counsel) which may be paid or incurred by the Administrative Agent or any
Creditor in enforcing, or obtaining advice of counsel in respect of, any rights
with respect to, or collecting, any or all of the Obligations and/or enforcing
any rights with respect to, or collecting against, such Guarantor under this
Guarantee. This Guarantee shall remain in full force and effect until the
Obligations are paid in full and the Aggregate Commitments are terminated,
notwithstanding that from time to time prior thereto no amounts may be
outstanding under the Credit Agreement.

                  (d) Each Guarantor agrees that the Obligations may at any time
and from time to time exceed the amount of the liability of such Guarantor
hereunder without impairing this Guarantee or affecting the rights and remedies
of the Administrative Agent or any Creditor hereunder.

                  (e) No payment or payments made by the Borrower, the
Guarantor, any other guarantor or any other Person or received or collected by
the Administrative Agent or any Creditor from the Borrower, any Guarantor, any
other guarantor or any other Person by virtue of any action or proceeding or any
set-off or appropriation or application at any time or from time to time in
reduction of or in payment of the Obligations shall be deemed to modify, reduce,
release or otherwise affect the liability of any Guarantor hereunder which
shall, notwithstanding any such payment or payments (other than payments made by
the Borrower or such Guarantor in respect of the Obligations or payments
received or collected from such Guarantor in respect of the Obligations), remain
liable for the Obligations up to the maximum liability of such Guarantor
hereunder until the Obligations are paid in full and the Aggregate Commitments
are terminated.




                                      -3-
<PAGE>

                  (f) Each Guarantor agrees that whenever, at any time, or from
time to time, it shall make any payment to the Administrative Agent or any
Creditor on account of its liability hereunder, it will notify the
Administrative Agent in writing that such payment is made under this Guarantee
for such purpose.

         2.2 Right of Contribution. Each Guarantor hereby agrees that to the
extent that a Guarantor shall have paid more than its proportionate share of any
payment made hereunder, such Guarantor shall be entitled to seek and receive
contribution from and against any other Guarantor hereunder who has not paid its
proportionate share of such payment. Each Guarantor's right of contribution
shall be subject to the terms and conditions of subsection 2.4 hereof. The
provisions of this subsection shall in no respect limit the obligations and
liabilities of any Guarantor to the Administrative Agent and the Creditors, and
each Guarantor shall remain liable to the Administrative Agent and the Creditors
for the full amount guaranteed by such Guarantor hereunder.

         2.3 Right of Set-off. During the continuance of any Event of Default,
each Guarantor hereby irrevocably authorizes each Creditor at any time and from
time to time without notice to such Guarantor or any other Guarantor, any such
notice being expressly waived by each Guarantor, to set-off and appropriate and
apply any and all deposits (general or special, time or demand, provisional or
final, but excluding deposits held by such Guarantor as a fiduciary for others),
in any currency, and any other credits, indebtedness or claims, in any currency,
in each case whether direct or indirect, absolute or contingent, matured or
unmatured, at any time held or owing by such Creditor to or for the credit or
the account of such Guarantor, or any part thereof in such amounts as such
Creditor may elect, against and on account of the obligations and liabilities of
such Guarantor to such Creditor hereunder and claims of every nature and
description of such Creditor against such Guarantor, in any currency, whether
arising hereunder, under the Credit Agreement, any Note, any Loan Documents or
otherwise, as such Creditor may elect, whether or not the Administrative Agent
or any Creditor has made any demand for payment and although such obligations,
liabilities and claims may be contingent or unmatured. Such Creditor shall
notify such Guarantor and the Administrative Agent promptly of any such set-off
and the application made by such Creditor, provided that the failure to give
such notice shall not affect the validity of such set-off and application. The
rights of each Creditor under this subsection are in addition to other rights
and remedies (including, without limitation, other rights of set-off) which the
Administrative Agent or such Creditor may have.

         2.4 No Subrogation. Notwithstanding any payment or payments made by any
of the Guarantors hereunder or any set-off or application of funds of any of the
Guarantors by any Creditor, no Guarantor shall be entitled to be subrogated to
any of the rights of the Administrative Agent or any Creditor against the
Borrower or any other Guarantor or any collateral security or guarantee or right
of offset held by any Creditor for the payment of the Obligations until all
amounts owing to the Administrative Agent and the Creditors by the Borrower on
account of the Obligations are paid in full and the Aggregate Commitments are
terminated, nor shall any Guarantor seek or be entitled to seek any contribution
or reimbursement from the Borrower or any other Guarantor in respect of payments
made by such Guarantor hereunder until all amounts owing to the Administrative
Agent and the Creditors by the Borrower on account of the Obligations are paid
in full and the Aggregate Commitments are terminated. If any amount shall be
paid to any Guarantor on account of such subrogation rights






                                      -4-
<PAGE>

at any time when all of the Obligations shall not have been paid in full, such
amount shall be held by such Guarantor in trust for the Administrative Agent and
the Creditors, segregated from other funds of such Guarantor, and shall,
forthwith upon receipt by such Guarantor, be turned over to the Administrative
Agent in the exact form received by such Guarantor (duly indorsed by such
Guarantor to the Administrative Agent, if required), to be applied against the
Obligations, whether matured or unmatured, in such order as the Administrative
Agent may determine.

         2.5 Amendments, etc. with respect to the Obligations; Waiver of Rights.
Each Guarantor shall remain obligated hereunder notwithstanding that, without
any reservation of rights against any Guarantor and without notice to or further
assent by any Guarantor: (a) any demand for payment of any of the Obligations
made by the Administrative Agent or any Creditor may be rescinded by such party
and any of the Obligations continued; (b) the Obligations, or the liability of
any other party upon or for any part thereof, or any collateral security or
guarantee therefor or right of offset with respect thereto, may, from time to
time, in whole or in part, be renewed, extended, amended, modified, accelerated,
compromised, waived, surrendered or released by the Administrative Agent or any
Creditor (with the consent of the applicable Loan Parties where required by the
terms hereof or thereof); (c) the Credit Agreement, the Notes and the other Loan
Documents and any other documents executed and delivered in connection therewith
may be amended, modified, supplemented or terminated, in whole or in part, as
the Administrative Agent (or the Lenders or the Required Lenders, as the case
may be) and the applicable Loan Parties may deem advisable from time to time;
and (d) any collateral security, guarantee or right of offset at any time held
by the Administrative Agent or any Creditor for the payment of the Obligations
may be sold, exchanged, waived, surrendered or released. Neither the
Administrative Agent nor any Creditor shall have any obligation to protect,
secure, perfect or insure any Lien at any time held by it as security for the
Obligations or for this Guarantee or any property subject thereto. When making
any demand hereunder against any of the Guarantors, the Administrative Agent or
any Creditor may, but shall be under no obligation to, make a similar demand on
the Borrower or any other Guarantor or guarantor, and any failure by the
Administrative Agent or any Creditor to make any such demand or to collect any
payments from the Borrower or any such other Guarantor or guarantor or any
release of the Borrower or such other Guarantor or guarantor shall not relieve
any of the Guarantors in respect of which a demand or collection is not made or
any of the Guarantors not so released of their several obligations or
liabilities hereunder, and shall not impair or affect the rights and remedies,
express or implied, or as a matter of law, of the Administrative Agent or any
Creditor against any of the Guarantors. For the purposes hereof "demand" shall
include the commencement and continuance of any legal proceedings.

         2.6 Guarantee Absolute and Unconditional. Each Guarantor waives any and
all notice of the creation, renewal, extension or accrual of any of the
Obligations and notice of or proof of reliance by the Administrative Agent or
any Creditor upon this Guarantee or acceptance of this Guarantee, the
Obligations, and any of them, shall conclusively be deemed to have been created,
contracted or incurred, or renewed, extended, amended or waived, in reliance
upon this Guarantee. All dealings between the Borrower and any of the
Guarantors, on the one hand, and the Administrative Agent and the Creditors, on
the other hand, likewise shall be conclusively presumed to have been had or
consummated in reliance upon this Guarantee. Each Guarantor waives diligence,
presentment, protest, demand for payment and notice of default or nonpayment to
or upon the Borrower or any of the Guarantors with respect to the Obligations.
Each






                                      -5-
<PAGE>

Guarantor understands and agrees that this Guarantee shall be construed as a
continuing, absolute and unconditional guarantee of payment without regard to
(a) the validity, regularity or enforceability of the Credit Agreement, any Note
or any other Loan Document, any of the Obligations or any other collateral
security therefor or guarantee or right of offset with respect thereto at any
time or from time to time held by the Administrative Agent or any Creditor, (b)
any defense, set-off or counterclaim (other than a defense of payment or
performance) which may at any time be available to or be asserted by the
Borrower against the Administrative Agent or any Creditor, or (c) any other
circumstance whatsoever (with or without notice to or knowledge of the Borrower
or such Guarantor) which constitutes, or might be construed to constitute, an
equitable or legal discharge of the Borrower for the Obligations, or of such
Guarantor under this Guarantee, in bankruptcy or in any other instance. When
pursuing its rights and remedies hereunder against any Guarantor, the
Administrative Agent and any Creditor may, but shall be under no obligation to,
pursue such rights and remedies as it may have against the Borrower or any other
Person or against any collateral security or guarantee for the Obligations or
any right of offset with respect thereto, and any failure by the Administrative
Agent or any Creditor to pursue such other rights or remedies or to collect any
payments from the Borrower or any such other Person or to realize upon any such
collateral security or guarantee or to exercise any such right of offset, or any
release of the Borrower or any such other Person or any such collateral
security, guarantee or right of offset, shall not relieve such Guarantor of any
liability hereunder, and shall not impair or affect the rights and remedies,
whether express, implied or available as a matter of law, of the Administrative
Agent and the Creditors against such Guarantor. This Guarantee shall remain in
full force and effect and be binding in accordance with and to the extent of its
terms upon each Guarantor and the successors and assigns thereof, and shall
inure to the benefit of the Administrative Agent and the Creditors, and their
respective successors, indorsees, transferees and assigns, until all the
Obligations and the obligations of each Guarantor under this Guarantee shall
have been satisfied by payment in full and the Aggregate Commitments shall be
terminated, notwithstanding that from time to time during the term of the Credit
Agreement no amounts may be outstanding under the Credit Agreement.

         2.7 Reinstatement. This Guarantee shall continue to be effective, or be
reinstated, as the case may be, if at any time payment, or any part thereof, of
any of the Obligations is rescinded or must otherwise be restored or returned by
the Administrative Agent or any Creditor upon the insolvency, bankruptcy,
dissolution, liquidation or reorganization of the Borrower or any Guarantor, or
upon or as a result of the appointment of a receiver, intervenor or conservator
of, or trustee or similar officer for, the Borrower or any Guarantor or any
substantial part of its property, or otherwise, all as though such payments had
not been made.

         2.8 Payments. Each Guarantor hereby guarantees that payments hereunder
will be paid to the Administrative Agent without set-off or counterclaim in U.S.
Dollars at the office of the Administrative Agent located at 270 Park Avenue,
New York, New York 10017.

                                    SECTION 3
                         REPRESENTATIONS AND WARRANTIES

         3.1 Representations and Warranties. Each Guarantor hereby represents
and warrants that, in the case of such Guarantor, the representations and
warranties set forth in Section 5 of the Credit Agreement as they relate to such
Guarantor or to the other Loan Documents to which such






                                      -6-
<PAGE>

Guarantor is a party, each of which is hereby incorporated herein by reference,
are true and correct, and the Administrative Agent and each Creditor shall be
entitled to rely on each of them as if they were fully set forth herein,
provided that each reference in each such representation and warranty to the
Borrower's knowledge shall, for the purposes of this Section 3, be deemed to be
a reference to such Guarantor's knowledge.

         Each Guarantor agrees that the foregoing representations and warranties
shall be deemed to have been made by such Guarantor on the date of (a) each Loan
or (b) the issuance of any Letter of Credit under the Credit Agreement or (c)
each Hedging Agreement on and as of such date as though made hereunder on and as
of such date (except to the extent that such representations and warranties are
expressly made only as of an earlier date, in which case such representations
and warranties shall have been true and correct on and as of such earlier date).

                                    SECTION 4
                                    COVENANTS

         4.1 Covenants. Each Guarantor hereby covenants and agrees with the
Administrative Agent and each Creditor that, from and after the date of this
Guarantee until the Obligations are paid in full and the Aggregate Commitments
and Hedge Agreements with a Creditor are terminated, such Guarantor shall take,
or shall refrain from taking, as the case may be, each action that is necessary
to be taken or not taken, as the case may be, so that no Default or Event of
Default is caused by the failure to take such action or to refrain from taking
such action by such Guarantor or any of its Subsidiaries.

         4.2 Authority of Administrative Agent. Each Guarantor acknowledges that
the rights and responsibilities of the Administrative Agent under this Guarantee
with respect to any action taken by the Administrative Agent or the exercise or
non-exercise by the Administrative Agent of any option, right, request, judgment
or other right or remedy provided for herein or resulting or arising out of this
Guarantee shall, as between the Administrative Agent and the other Creditors, be
governed by the Credit Agreement and by such other agreements with respect
thereto as may exist from time to time among them, but, as between the
Administrative Agent and such Guarantor, the Administrative Agent shall be
conclusively presumed to be acting as agent for the Creditors with full and
valid authority so to act or refrain from acting in the manner set forth in
Section 10 of the Credit Agreement, and no Guarantor shall be under any
obligation, or entitlement, to make any inquiry respecting such authority.

         4.3 Subordination of Indebtedness.

                  (a) Subordination of All Guarantor Claims. After and during
the continuation of an Event of Default, no Guarantor shall receive or collect,
directly or indirectly, from any obligor in respect thereof any amount upon the
Guarantor Claims.

                  (b) Claims in Bankruptcy. In the event of receivership,
bankruptcy, reorganization, arrangement, debtor's relief, or other insolvency
proceedings involving any Guarantor, the Administrative Agent on behalf of the
Administrative Agent and the Creditors shall have the right to prove their claim
in any proceeding, so as to establish their rights hereunder and receive
directly from the receiver, trustee or other court custodian, dividends and




                                      -7-
<PAGE>

payments which would otherwise be payable upon Guarantor Claims. Each Guarantor
hereby assigns such dividends and payments to the Administrative Agent for the
benefit of the Administrative Agent and the Creditors for application against
the Obligations in such order as the Administrative Agent may elect or the
Required Lenders may direct. Should any Agent or Creditor receive, for
application upon the Obligations, any such dividend or payment which is
otherwise payable to any Guarantor, and which, as between such Guarantors, shall
constitute a credit upon the Guarantor Claims, then upon payment in full in cash
of the Obligations, the expiration of all Letters of Credit outstanding under
the Credit Agreement and the termination of all of the Commitments, the intended
recipient shall become subrogated to the rights of the Administrative Agent and
the Creditors to the extent that such payments to the Administrative Agent and
the Creditors on the Guarantor Claims have contributed toward the liquidation of
the Obligations, and such subrogation shall be with respect to that proportion
of the Obligations which would have been unpaid if the Administrative Agent and
the Creditors had not received dividends or payments upon the Guarantor Claims.

                  (c) Payments Held in Trust. In the event that, notwithstanding
subsection 4.3(a) and subsection 4.3(b), any Guarantor should receive any funds,
payments, claims or distributions which are prohibited by such subsections, then
it agrees: (i) to hold in trust for the Administrative Agent and the Creditors
an amount equal to the amount of all funds, payments, claims or distributions so
received, and (ii) that it shall have absolutely no dominion over the amount of
such funds, payments, claims or distributions except to pay them promptly to the
Administrative Agent, for the benefit of the Creditors; and each Guarantor
covenants promptly to pay the same to the Administrative Agent.

                  (d) Liens Subordinate. Each Guarantor agrees that, until the
Obligations are paid in full in cash, no Letter of Credit shall be outstanding
and the termination of the Aggregate Commitments and Hedge Agreements with a
Creditor, any Liens securing payment of the Guarantor Claims shall be and remain
inferior and subordinate to any Liens securing payment of the Obligations,
regardless of whether such encumbrances in favor of such Guarantor, the
Administrative Agent or any Creditor presently exist or are hereafter created or
attach. Without the prior written consent of the Administrative Agent, no
Guarantor, during the period in which any of the Obligations are outstanding or
the Commitments are in effect, shall (i) exercise or enforce any creditor's
right it may have against any debtor in respect of the Guarantor Claims, or (ii)
foreclose, repossess, sequester or otherwise take steps or institute any action
or proceeding (judicial or otherwise, including without limitation the
commencement of or joinder in any liquidation, bankruptcy, rearrangement,
debtor's relief or insolvency proceeding) to enforce any Lien held by it in
respect of Guarantor Claims.

                  (e) Notation of Records. Upon the request of the
Administrative Agent, all promissory notes and all accounts receivable ledgers
or other evidence of the Guarantor Claims accepted by or held by any Guarantor
shall contain a specific written notice thereon that the indebtedness evidenced
thereby is subordinated under the terms of this Agreement.





                                      -8-
<PAGE>

                                    SECTION 5
                                  MISCELLANEOUS

         5.1 Notices. All notices, requests and demands to or upon the
Administrative Agent or any Guarantor to be effective shall be in writing
(including by facsimile transmission) and, unless otherwise expressly provided
herein, shall be deemed to have been duly given or made (a) in the case of
delivery by hand or by courier service, when delivered, (b) in the case of
delivery by mail, three Business Days after being deposited in the mails,
postage prepaid, or (c) in the case of delivery by facsimile transmission, when
sent and receipt has been confirmed, addressed (x) if to the Administrative
Agent, at its address or transmission number for notices provided in subsection
11.2 of the Credit Agreement and (y) if to any Guarantor, at its address or
transmission number for notices set forth on Schedule 1 hereto. The
Administrative Agent and any Guarantor may change its address and transmission
numbers for notices by notice in the manner provided in this subsection 5.1.

         5.2 Counterparts. This Guarantee may be executed by one or more of the
Guarantors on any number of separate counterparts, and all of said counterparts
taken together shall be deemed to constitute one and the same instrument. A set
of the counterparts of this Guarantee signed by all the Guarantors shall be
lodged with the Administrative Agent.

         5.3 Severability. Any provision of this Guarantee which is prohibited
or unenforceable in any jurisdiction shall, as to such jurisdiction, be
ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render
unenforceable such provision in any other jurisdiction.

         5.4 Integration. This Guarantee represents the agreement of each
Guarantor with respect to the subject matter hereof and there are no promises,
undertakings, representations or warranties by the Administrative Agent or any
Creditor relative to the subject matter hereof not reflected herein.

         5.5 Amendments in Writing; No Waiver; Cumulative Remedies.

                  (a) None of the terms or provisions of this Guarantee may be
waived, amended, supplemented or otherwise modified except by a written
instrument executed by each Guarantor and the Administrative Agent in accordance
with subsection 11.1 of the Credit Agreement.

                  (b) Neither the Administrative Agent nor any Creditor shall by
any act (except by a written instrument pursuant to subsection 5.5(a) hereof),
delay, indulgence, omission or otherwise be deemed to have waived any right or
remedy hereunder or to have acquiesced in any Default or Event of Default or in
any breach of any of the terms and conditions hereof. No failure to exercise and
no delay in exercising, on the part of the Administrative Agent or any Creditor,
any right, remedy, power or privilege hereunder shall operate as a waiver
thereof; nor shall any single or partial exercise of any right, remedy, power or
privilege hereunder preclude any other or further exercise thereof or the
exercise of any other right, remedy, power or privilege. A waiver by the
Administrative Agent or any Creditor of any right or remedy






                                      -9-
<PAGE>

hereunder on any one occasion shall not be construed as a bar to any right or
remedy which the Administrative Agent or such Creditor would otherwise have on
any future occasion.

                  (c) The rights and remedies herein provided are cumulative and
not exclusive of any other rights, remedies, powers and privileges provided by
law.

         5.6 Loan Documents. Each Guarantor agrees that this Guarantee shall
constitute a "Loan Document" under the Credit Agreement and that they shall be
deemed to be "Loan Parties", as such term is defined in the Credit Agreement.

         5.7 Section Headings. The section headings used in this Guarantee are
for convenience of reference only and are not to affect the construction hereof
or be taken into consideration in the interpretation hereof.

         5.8 Successors and Assigns. This Guarantee shall be binding upon the
successors and assigns of each Guarantor and shall inure to the benefit of the
Administrative Agent and the Creditors and their successors and assigns.

         5.9 GOVERNING LAW. THIS GUARANTEE AND THE RIGHTS AND OBLIGATIONS OF THE
PARTIES HEREUNDER SHALL BE GOVERNED BY, AND CONSTRUED AND INTERPRETED IN
ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK, WITHOUT REGARD TO CONFLICTS
OF LAW PRINCIPLES THAT WOULD RESULT IN THE APPLICATION OF THE LAWS OF A
DIFFERENT JURISDICTION.

         5.10 Submission to Jurisdiction; Waivers. Each Guarantor hereby
irrevocably and unconditionally:

                  (a) submits for itself and its Property in any legal action or
proceeding relating to this Agreement and the other Loan Documents to which it
is a party, or for recognition and enforcement of any judgment in respect
thereof, to the non-exclusive general jurisdiction of the Courts of the State of
New York, the courts of the United States of America for the Southern District
of New York, and appellate courts from any thereof;

                  (b) consents that any such action or proceeding may be brought
in such courts and waives any objection that it may now or hereafter have to the
venue of any such action or proceeding in any such court or that such action or
proceeding was brought in an inconvenient court and agrees not to plead or claim
the same;

                  (c) agrees that service of process in any such action or
proceeding may be effected by mailing a copy thereof by registered or certified
mail (or any substantially similar form of mail), postage prepaid, to the
Guarantor at its address set forth in Schedule 1 hereto or at such other address
of which the Administrative Agent shall have been notified pursuant to
subsection 5.1;

                  (d) agrees that nothing herein shall affect the right to
effect service of process in any other manner permitted by law or shall limit
the right to sue in any other jurisdiction; and




                                      -10-
<PAGE>

                  (e) waives, to the maximum extent not prohibited by law, any
right it may have to claim or recover in any legal action or proceeding referred
to in this subsection any special, exemplary, punitive or consequential damages.

         5.11 Acknowledgments. Each Guarantor hereby acknowledges that:

                  (a) it has been advised by counsel in the negotiation,
execution and delivery of this Agreement and the other Loan Documents;

                  (b) no Agent nor any Creditor has any fiduciary relationship
with or duty to such Guarantor arising out of or in connection with this
Agreement or any of the other Loan Documents, and the relationship between the
Agents and the Creditors, on one hand, and such Guarantor, on the other hand, in
connection herewith or therewith is solely that of guarantor and creditor; and

                  (c) no joint venture is created hereby or by the other Loan
Documents or otherwise exists by virtue of the transactions contemplated hereby
among the Agents and the other Creditors or among the Borrower, the Agents and
the other Creditors.

         5.12 WAIVERS OF JURY TRIAL. THE PARTIES HERETO HEREBY KNOWINGLY AND
INTENTIONALLY, IRREVOCABLY AND UNCONDITIONALLY WAIVE TRIAL BY JURY IN ANY LEGAL
ACTION OR PROCEEDING RELATING TO THIS AGREEMENT OR ANY OTHER LOAN DOCUMENT AND
FOR ANY COUNTERCLAIM THEREIN.

         5.13 Additional Obligors. Each Restricted Subsidiary of the Borrower
that is required to become a party to this Guarantee pursuant to subsection
7.9(c) of the Credit Agreement shall become a Guarantor for all purposes of this
Guarantee upon execution and delivery by such Subsidiary of an assumption
agreement in the form of Schedule 2 hereto (each an "Assumption Agreement").

         5.14 Release. At the request and sole expense of the Borrower, a
Guarantor shall be released from its obligations hereunder in the event that all
the capital stock of such Guarantor shall be sold, transferred or otherwise
disposed of in a transaction permitted by the Credit Agreement; provided that
the Borrower shall have delivered to the Administrative Agent, at least five
Business Days prior to the date of the proposed release, a written request for
release identifying the relevant Guarantor and the terms of the sale or other
disposition in reasonable detail, including the price thereof and any expenses
in connection therewith, together with a certification by the Borrower stating
that such transaction is in compliance with the Credit Agreement and the other
Loan Documents.




                                      -11-
<PAGE>



IN WITNESS WHEREOF, the undersigned has caused this Agreement to be duly
executed and delivered as of the date first above written.

                             WESTPORT FINANCE CO.


                             By:      /s/ LON MCCAIN
                                      ------------------------------------------
                                      Lon McCain, Treasurer


                             WHL, INC.


                             By:      /s/ LON MCCAIN
                                      ------------------------------------------
                                      Lon McCain, Vice President, Treasurer and
                                      Chief Financial Officer


                             WHG, INC.


                             By:      /s/ LON MCCAIN
                                      ------------------------------------------
                                      Lon McCain, Vice President, Treasurer and
                                      Chief Financial Officer


                             WESTPORT OIL AND GAS COMPANY, L.P.
                                 by WHG, Inc., its sole general partner


                             By:      /s/ LON MCCAIN
                                      ------------------------------------------
                                      Lon McCain, Vice President, Treasurer and
                                      Chief Financial Officer

                             WESTPORT CANADA LLC
                                 by Westport Oil and Gas Company, L.P.,
                                   its sole member, a Delaware general
                                     partnership by WHG, Inc. its sole
                                       general partner


                                 By:     /s/ LON MCCAIN
                                         ---------------------------------------
                                           Lon McCain, Vice President,
                                           Treasurer and Chief Financial Officer


                      Signature Page - Subsidiary Guarantee


<PAGE>
                       JERRY CHAMBERS EXPLORATION COMPANY
                           by Westport Oil and Gas Company, L.P.,
                             its sole member, a Delaware general partnership
                               by WHG, Inc. its general partner


                              By:      /s/ LON MCCAIN
                                       -----------------------------------------
                                       Lon McCain, Vice President, Treasurer
                                       and Chief Financial Officer


                       WESTPORT ARGENTINA LLC


                       By:         /s/ DONALD D. WOLF
                                   ---------------------------------------------
                                   Donald D. Wolf, Manager


                       WESTPORT OVERRIDING ROYALTY
                           LLC by Westport Oil and Gas Company, L.P.,
                             its sole member, a Delaware limited partnership
                               by WHG, Inc. its sole general partner


                              By:     /s/ LON MCCAIN
                                      ------------------------------------------
                                      Lon McCain, Vice President, Treasurer
                                      and Chief Financial Officer


                       HORSE CREEK TRADING & COMPRESSION LLC
                           by Westport Oil and Gas Company, L.P.,
                             its sole member and manager,
                               a Delaware limited partnership
                                by WHG, Inc. its sole general partner



                              By:     /s/ LON MCCAIN
                                      ------------------------------------------
                                      Lon McCain, Vice President, Treasurer
                                      and Chief Financial Officer




                      Signature Page - Subsidiary Guarantee


<PAGE>



                       WESTPORT FIELD SERVICES, LLC
                           by Westport Resources Corporation,
                             its sole member and manager


                             By: /s/ LON MCCAIN
                                 ------------------------------------------
                                 Lon McCain, Vice President, Treasurer and
                                 Chief Financial Officer


                      Signature Page - Subsidiary Guarantee


<PAGE>

                                   SCHEDULE 1
                               ADDRESS FOR NOTICES

<Table>
<S>                                                          <C>
Westport Finance Co.                                         WHL, Inc.
1670 Broadway Street, Suite 2800                             1670 Broadway Street, Suite 2800
Denver, Colorado 80202                                       Denver, Colorado 80202
Phone:   303-573-5404                                        Phone: 303-573-5404
Fax:  303-5735609                                            Fax:  303-5735609
Attention:  Lon McCain                                       Attention:  Lon McCain

WHG, Inc.                                                    Westport Oil and Gas Company, L.P.
1670 Broadway Street, Suite 2800                             1670 Broadway Street, Suite 2800
Denver, Colorado 80202                                       Denver, Colorado 80202
Phone:   303-573-5404                                        Phone:   303-573-5404
Fax:  303-5735609                                            Fax:  303-5735609
Attention:  Lon McCain                                       Attention:  Lon McCain

Jerry Chambers Exploration Company                           Westport Canada LLC
Denver, Colorado 80202                                       1670 Broadway Street, Suite 2800
1670 Broadway Street, Suite 2800                             Denver, Colorado 80202
Denver, Colorado 80202                                       Phone:   303-573-5404
Phone:   303-573-5404                                        Fax:  303-5735609
Fax:  303-5735609                                            Attention:  Lon McCain
Attention:  Lon McCain

Westport Argentina LLC                                       Westport Overriding Royalty LLC
1670 Broadway Street, Suite 2800                             1670 Broadway Street, Suite 2800
Denver, Colorado 80202                                       Denver, Colorado 80202
Phone:   303-573-5404                                        Phone:   303-573-5404
Fax:  303-5735609                                            Fax:  303-5735609
Attention:  Lon McCain                                       Attention:  Lon McCain

Horse Creek Trading & Compression LLC                        Westport Field Services, LLC
1670 Broadway Street, Suite 2800                             1670 Broadway Street, Suite 2800
Denver, Colorado 80202                                       Denver, Colorado 80202
Phone:   303-573-5404                                        Phone:   303-573-5404
Fax:  303-5735609                                            Fax:  303-5735609
Attention:  Lon McCain                                       Attention:  Lon McCain
</Table>


                                  Schedule 1-1

<PAGE>


                                   SCHEDULE 2
                                  TO GUARANTEE

                          FORM OF ASSUMPTION AGREEMENT

         ASSUMPTION AGREEMENT, dated as of ________________, 200__, is made by
______________________________, a ______________ (the "Additional Obligor"), in
favor of JPMORGAN CHASE BANK as administrative agent (in such capacity, the
"Administrative Agent") for the banks and other financial institutions (the
"Lenders") parties to the Credit Agreement referred to below and all other
Creditors. All capitalized terms not defined herein shall have the meaning
ascribed to them in the Guarantee referred to below.

                                    RECITALS

         A. Westport Resources Corporation, a Nevada corporation (the
"Borrower"), the Administrative Agent, the Syndication Agent, the Documentation
Agents, and the Lenders have entered into a Credit Agreement, dated as of
December 17, 2002 (as amended, supplemented or otherwise modified from time to
time, the "Credit Agreement").

         B. In connection with the Credit Agreement, certain Restricted
Subsidiaries (other than the Additional Obligor) have entered into the
Subsidiary Guarantee, dated as of even date with the Credit Agreement (as
amended, supplemented or otherwise modified from time to time, the "Guarantee")
in favor of the Administrative Agent and the Creditors.

         C. The Credit Agreement requires the Additional Obligor to become a
party to the Guarantee.

         D. The Additional Obligor has agreed to execute and deliver this
Assumption Agreement in order to become a party to the Guarantee.

         E. Now, therefore, it is agreed:

         1. Guarantee. By executing and delivering this Assumption Agreement,
the Additional Obligor, as provided in subsection 5.13 of the Guarantee, hereby
becomes a party to the Guarantee as a Guarantor thereunder with the same force
and effect as if originally named therein as a Guarantor and, without limiting
the generality of the foregoing, hereby expressly assumes all obligations and
liabilities of a Guarantor thereunder and expressly guarantees, jointly and
severally, to the Creditors the Obligations. The Additional Obligor hereby
represents and warrants that each of the representations and warranties
contained in Section 3 of the Guarantee is true and correct on and as of the
date hereof (after giving effect to this Assumption Agreement) as if made on and
as of such date.

         2. GOVERNING LAW. THIS ASSUMPTION AGREEMENT AND THE RIGHTS AND
OBLIGATIONS OF THE PARTIES HEREUNDER SHALL BE GOVERNED BY, AND CONSTRUED AND
INTERPRETED IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK, WITHOUT REGARD
TO CONFLICTS OF LAW PRINCIPLES THAT WOULD RESULT IN THE APPLICATION OF THE LAWS
OF A DIFFERENT JURISDICTION.


                                  Schedule 2-1
<PAGE>

         IN WITNESS WHEREOF, the undersigned has caused this Assumption
Agreement to be duly executed and delivered as of the date first above written.

                                          [ADDITIONAL OBLIGOR]



                                          By:
                                             ----------------------------------
                                            Name:
                                                 ------------------------------
                                            Title:
                                                  -----------------------------




                                  Schedule 2-2