<PAGE>
                                                                    EXHIBIT 10.9


[CANADIAN AGENT WILL ADVISE THE CANADIAN LENDERS OF THE DATE ON WHICH CANADIAN
BORROWER EXECUTES AND DELIVERS THIS AMENDMENT TO CANADIAN AGENT.]


                  FOURTH AMENDMENT TO CANADIAN CREDIT AGREEMENT


         The Offer for Extension set forth in this Fourth Amendment to Canadian
Credit Agreement (herein called this "Amendment") is made by Bank of America
Canada, individually and as administrative agent ("Canadian Agent"), and the
undersigned Canadian Lenders party to the Original Agreement defined below
("Canadian Lenders") and shall be open for acceptance by Northstar Energy
Corporation, an Alberta corporation ("Canadian Borrower") until (and including)
August 21, 2001.


                                   WITNESSETH:

         WHEREAS, Canadian Borrowers, Canadian Agent and Canadian Lenders have
entered into that certain Canadian Credit Agreement dated as of August 29, 2000
(as amended, supplemented, or restated to the date hereof, the "Original
Agreement"), for the purpose and consideration therein expressed, whereby
Canadian Lenders became obligated to make loans to Canadian Borrowers as therein
provided; and

         WHEREAS, on January 1, 2001 Northstar Energy, Devon Energy Canada
Holding Corporation (the successor by amalgamation to Devon Energy Canada) and
certain other Alberta corporations, all of which were Subsidiaries of US
Borrower, amalgamated under the name Northstar Energy Corporation (defined above
as the "Canadian Borrower") which is now the sole Canadian Borrower; and

         WHEREAS, pursuant to Section 1.6 of the Original Agreement, Canadian
Borrower has delivered to Canadian Agent a Request for Offer of Extension and a
copy thereof has been provided to all Canadian Lenders; and

         WHEREAS, all of the Canadian Lenders have agreed to accept such Request
for Offer of Extension; and

         WHEREAS, all of the Canadian Lenders have agreed to extend the Canadian
Revolving Period until the Conversion Date as described in Section 2.1 of this
Amendment and Canadian Agent hereby makes an Offer of Extension to Canadian
Borrower on such terms;

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements contained herein and in the Original Agreement, in
consideration of the loans which


                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>

may hereafter be made by Canadian Lenders to Canadian Borrower, and for other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto do hereby agree as follows:

                                   ARTICLE I.

                           Definitions and References

         Section 1.1. Terms Defined in the Original Agreement. Unless the
context otherwise requires or unless otherwise expressly defined herein, the
terms defined in the Original Agreement shall have the same meanings whenever
used in this Amendment.

         Section 1.2. Other Defined Terms. Unless the context otherwise
requires, the following terms when used in this Amendment shall have the
meanings assigned to them in this Section 1.2.

                  "Amendment" means this Fourth Amendment to Canadian Credit
         Agreement.

                  "Canadian Agreement" means the Original Agreement as amended
         hereby.


                                   ARTICLE II.

                        Amendments to Original Agreement

         Section 2.1. Defined Terms.

         (a) The definition of "Conversion Date" in Annex I of the Original
Agreement is hereby amended in its entirety to read as follows:

                           "'Conversion Date' means the date which is 364 days
                  after the date on which Canadian Borrower executes and
                  delivers to Canadian Agent the Fourth Amendment to Canadian
                  Credit Agreement among Canadian Borrower, Canadian Agent and
                  Canadian Lenders, or such later day to which the Conversion
                  Date is extended pursuant to Section 1.6 of the Canadian
                  Agreement."

         Section 2.2. Waiver of Notice. Each Canadian Lender hereby waives the
requirement under Section 1.6 of the Original Agreement that a Request for Offer
of Extension be made by a specific date prior to the current Conversion Date of
August 28, 2001.

         Section 2.3. Lenders Schedule. Annex II to this Amendment is hereby
substituted for Annex II to the Original Agreement.


                                       2


                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>

                                  ARTICLE III.

                           Conditions of Effectiveness

         Section 3.1. Effective Date. This Amendment shall become effective on
the date on which Canadian Borrower has executed and delivered this Amendment to
Canadian Agent (provided that Canadian Borrower shall have executed this
Amendment on or before August 21, 2001) and the following additional conditions
are satisfied:

         (a) Canadian Agent shall have received all of the following, at
Canadian Agent's office, duly executed and delivered and in form and substance
satisfactory to Canadian Agent, all of the following:

                  (i) this Amendment executed by Canadian Borrower, Canadian
         Agent and all Canadian Lenders.

                  (ii) a certificate of the Chairman of the Board, President, or
         Vice President - Finance of Canadian Borrower dated the date of this
         Amendment certifying: (i) that all of the representations and
         warranties set forth in Article IV hereof are true and correct at and
         as of such date, and (ii) that no Default exists at and as of such
         date.

         (b) Canadian Borrower shall have paid, in connection with such Canadian
Loan Documents, all fees and reimbursements to be paid to Canadian Agent and
Canadian Lenders pursuant to any Canadian Loan Documents, or otherwise due
Canadian Agent or Canadian Lenders and including fees and disbursements of
Canadian Agent's attorneys.

         Section 3.2. Offer to Extend. The Offer to Extend set forth herein
shall be withdrawn and this Amendment shall be null and void if it is not
executed and delivered by Canadian Borrower on or before August 21, 2001.


                                   ARTICLE IV.

                         Representations and Warranties

         Section 4.1. Representations and Warranties of Canadian Borrower. In
order to induce each Canadian Lender to enter into this Amendment, Canadian
Borrower represents and warrants to each Canadian Lender that:

         (a) The representations and warranties contained in Article V of the
Original Agreement are true and correct at and as of the time of the
effectiveness hereof, except to the extent that the facts on which such
representations and warranties are based have been changed by the extension of
credit under the Canadian Agreement.


                                       3


                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>

         (b) Canadian Borrower is duly authorized to execute and deliver this
Amendment and is and will continue to be duly authorized to borrow monies and to
perform its obligations under the Canadian Agreement. Canadian Borrower has duly
taken all corporate action necessary to authorize the execution and delivery of
this Amendment and to authorize the performance of the obligations of Canadian
Borrower hereunder.

         (c) The execution and delivery by Canadian Borrower of this Amendment,
the performance by Canadian Borrower of its obligations hereunder and the
consummation of the transactions contemplated hereby do not and will not (i)
conflict with any provision of (A) any Law, (B) the organizational documents of
Canadian Borrower, or (C) any agreement, judgment, license, order or permit
applicable to or binding upon Canadian Borrower unless such conflict would not
reasonably be expected to have a Material Adverse Effect, or (ii) result in or
require the creation of any Lien upon any assets or properties of Canadian
Borrower which would reasonably be expected to have a Material Adverse Effect,
except as expressly contemplated or permitted in the Loan Documents. Except as
expressly contemplated in the Loan Documents no consent, approval, authorization
or order of, and no notice to or filing with, any Tribunal or third party is
required in connection with the execution, delivery or performance by Canadian
Borrower of this Amendment or to consummate any transactions contemplated by
this Amendment, unless failure to obtain such consent would not reasonably be
expected to have a Material Adverse Effect.

         (d) When duly executed and delivered, each of this Amendment and the
Canadian Agreement will be a legal and binding obligation of Canadian Borrower,
enforceable in accordance with its terms, except as limited by bankruptcy,
insolvency or similar laws of general application relating to the enforcement of
creditors' rights and by equitable principles of general application.

         (e) The audited annual Consolidated financial statements of US Borrower
dated as of December 31, 2000 and the unaudited quarterly Consolidated financial
statements of US Borrower dated as of March 31, 2001 fairly present the
Consolidated financial position at such dates and the Consolidated statement of
operations and the changes in Consolidated financial position for the periods
ending on such dates for US Borrower. Copies of such financial statements have
heretofore been delivered to each Canadian Lender. Since such dates no material
adverse change has occurred in the Consolidated financial condition or
businesses of US Borrower.


                                   ARTICLE V.

                                  Miscellaneous

         Section 5.1. Ratification of Agreements. The Original Agreement as
hereby amended are hereby ratified and confirmed in all respects. The Canadian
Loan Documents, as they may be amended or affected by this Amendment, are hereby
ratified and confirmed in all respects. Any reference to the Canadian Agreement
in any Loan Document shall be deemed to be a reference to


                                       4


                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>

the Original Agreement as hereby amended. The execution, delivery and
effectiveness of this Amendment shall not, except as expressly provided herein,
operate as a waiver of any right, power or remedy of Canadian Lenders under the
Canadian Agreement or any other Canadian Loan Document nor constitute a waiver
of any provision of the Canadian Agreement or any other Canadian Loan Document.

         Section 5.2. Survival of Agreements. All representations, warranties,
covenants and agreements of Canadian Borrower herein shall survive the execution
and delivery of this Amendment and the performance hereof, including without
limitation the making or granting of the Loans, and shall further survive until
all of the Obligations are paid in full. All statements and agreements contained
in any certificate or instrument delivered by Canadian Borrower or any
Restricted Person hereunder or under the Canadian Agreement to any Canadian
Lender shall be deemed to constitute representations and warranties by, and/or
agreements and covenants of, Canadian Borrower under this Amendment and under
the Canadian Agreement.

         Section 5.3. Canadian Loan Documents. This Amendment is a Canadian Loan
Document, and all provisions in the Canadian Agreement pertaining to Canadian
Loan Documents apply hereto.

         Section 5.4. Governing Law. This Amendment shall be governed by and
construed in accordance the laws of the Province of Alberta and any applicable
laws of Canada in all respects, including construction, validity and
performance.

         Section 5.5. Counterparts; Fax. This Amendment may be separately
executed in counterparts and by the different parties hereto in separate
counterparts, each of which when so executed shall be deemed to constitute one
and the same Amendment. This Amendment may be validly executed by facsimile or
other electronic transmission.

         THIS AMENDMENT AND THE OTHER CANADIAN 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 OF THE PARTIES.


         [The remainder of this page has been intentionally left blank.]


                                       5


                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>

         IN WITNESS WHEREOF, this Amendment is executed by Canadian Borrower as
of August 13, 2001.



                                           NORTHSTAR ENERGY CORPORATION
                                           Canadian Borrower

                                           By:      /s/  Paul Brereton
                                                    ----------------------------
                                                    Paul Brereton
                                                    Vice President - Finance



                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>

         IN WITNESS WHEREOF, this Amendment is executed by Canadian Agent and
Canadian Lenders.



                                   BANK OF AMERICA CANADA
                                   Administrative Agent, Canadian LC Issuer and
                                   Lender

                                   By:    /s/  Nelson Liam
                                          --------------------------------------
                                          Name:   Nelson Liam
                                          Title:  Vice President

                                   ABN AMRO BANK CANADA
                                   Lender

                                   By:    /s/  Teresa Wu
                                          --------------------------------------
                                          Name:   Teresa Wu
                                          Title:  Vice President

                                   By:    /s/  Mark Bohn
                                          --------------------------------------
                                          Name:   Mark Bohn
                                          Title:  Group Vice President

                                   BANCFIRST
                                   Lender

                                   By:    /s/  Arthur B. Hobbs
                                          --------------------------------------
                                          Name:   Arthur B. Hobbs
                                          Title:  Vice President

                                   BANK OF TOKYO - MITSUBISHI (CANADA)
                                   Lender

                                   By:    /s/  Davis J. Stewart
                                          --------------------------------------
                                          Name:   Davis J. Stewart
                                          Title:  Vice President

                                   BANK ONE, NA CANADA BRANCH
                                   Lender

                                   By:    /s/  Ronald L. Dierker
                                          --------------------------------------
                                          Name:   Ronald L. Dierker
                                          Title:  Director, Capital Markets



                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>

                              BAYERISCHE LANDESBANK
                              GIROZENTRALE, TORONTO BRANCH
                              Lender

                              By:    /s/ Eckhart Mehler
                                     -------------------------------------------
                                     Name:   Eckhart Mehler
                                     Title:  Senior Vice President & Principal
                                             Officer

                              By:    /s/  Bernd Erpenbeck
                                     -------------------------------------------
                                     Name:   Bernd Erpenbeck
                                     Title:  Second Vice President

                              CANADIAN IMPERIAL BANK OF COMMERCE
                              Lender

                              By:    /s/  Joelle Schellenberg
                                     -------------------------------------------
                                     Name:   Joelle Schellenberg
                                     Title:  Director

                              By:    /s/  Chris A. Perks
                                     -------------------------------------------
                                     Name:   Chris A. Perks
                                     Title:  Executive Director

                              CITIBANK CANADA
                              Lender

                              By:    /s/  James K. G. Campbell
                                     -------------------------------------------
                                     Name:   James K. G. Campbell
                                     Title:  Vice President

                              CREDIT LYONNAIS NEW YORK BRANCH
                              Lender

                              By:    /s/  Philippe Soustra
                                     -------------------------------------------
                                     Name:   Philippe Soustra
                                     Title:  Executive Vice President


                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>



                                   CREDIT SUISSE FIRST BOSTON CANADA
                                   Lender

                                   By:    /s/  Peter Chauvin
                                          --------------------------------------
                                          Name:      Peter Chauvin
                                          Title:     Vice President

                                   By:    /s/  Bill McFarland
                                          --------------------------------------
                                          Name:      Bill McFarland
                                          Title:     Vice President

                                   DEUTSCHE BANK AG NEW YORK BRANCH
                                   AND/OR CAYMAN ISLANDS BRANCH
                                   Lender

                                   By:    /s/  Michael E. Keating
                                          --------------------------------------
                                          Name:      Michael E. Keating
                                          Title:     Managing Director

                                   By:    /s/  Joel Makowsky
                                          --------------------------------------
                                          Name:      Joel Makowsky
                                          Title:     Vice President

                                   FIRST UNION NATIONAL BANK
                                   Lender

                                   By:    /s/  David E. Humphreys
                                          --------------------------------------
                                          Name:      David E. Humphreys
                                          Title:     Vice President

                                   ROYAL BANK OF CANADA
                                   Lender

                                   By:    /s/  Lorne Gartner
                                          --------------------------------------
                                          Name:      Lorne Gartner
                                          Title:     Vice President

                                   SUNTRUST BANK, ATLANTA
                                   Lender

                                   By:    /s/  David J. Edge
                                          --------------------------------------
                                          Name:      David J.Edge
                                          Title:     Director


                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>


                              THE BANK OF NEW YORK
                              Lender

                              By:    /s/  Raymond J. Palmer
                                     -------------------------------------------
                                     Name:      Raymond J. Palmer
                                     Title:     Vice President

                              THE CHASE MANHATTAN BANK, TORONTO BRANCH
                              Lender

                              By:    /s/  Drew McDonald
                                     -------------------------------------------
                                     Name:      Drew McDonald
                                     Title:     Authorized Representative

                              By:    /s/  Christine Chan
                                     -------------------------------------------
                                     Name:      Christine Chan
                                     Title:     Authorized Representative

                              THE FUJI BANK, LIMITED
                              Lender

                              By:    /s/  Jacques Azagury
                                     -------------------------------------------
                                     Name:      Jacques Azagury
                                     Title:     Senior Vice President & Manager

                              UBS AG, STAMFORD BRANCH
                              Lender

                              By:    /s/  Susan Brunner
                                     -------------------------------------------
                                     Name:      Susan Brunner
                                     Title:     Associate Director

                              By:    /s/  Patricia O'Kicki
                                     -------------------------------------------
                                     Name:      Patricia O'Kicki
                                     Title:     Director

                              UMB BANK
                              Lender

                              By:    /s/  Derek K. Duncan
                                     -------------------------------------------
                                     Name:      Derek K. Duncan
                                     Title:     Vice President


                                   Fourth Amendment to Canadian Credit Agreement

<PAGE>

                                                                        ANNEX II


                                LENDERS SCHEDULE





                                   Fourth Amendment to Canadian Credit Agreement
<PAGE>

                                                                Fourth Amendment


                              CONSENT AND AGREEMENT


         Devon Energy Corporation, a Delaware corporation ("Canadian
Guarantor"), hereby (i) consents to the provisions of this Amendment and the
transactions contemplated herein, (ii) ratifies and confirms the Guaranty dated
as of August 29, 2000 made by it for the benefit of Canadian Agent and Lenders
executed pursuant to the Credit Agreement and the other Canadian Loan Documents,
(iii) agrees that all of its respective obligations and covenants thereunder
shall remain unimpaired by the execution and delivery of this Amendment and the
other documents and instruments executed in connection herewith, and (iv) agrees
that the Canadian Guaranty and such other Canadian Loan Documents shall remain
in full force and effect.



                                             DEVON ENERGY CORPORATION



                                             By:  /s/ Dale T. Wilson
                                                  ------------------------------
                                                  Dale T. Wilson
                                                  Treasurer

<PAGE>
                             COMPLIANCE CERTIFICATE

                          NORTHSTAR ENERGY CORPORATION


         Reference is made to that certain Fourth Amendment to Canadian Credit
Agreement dated as of August 13, 2001 (the "Fourth Amendment") among Northstar
Energy Corporation, ("Northstar"), Bank of America Canada, individually and as
administrative agent ("Canadian Agent"), and certain financial institutions
("Lenders"). Terms which are defined in the Fourth Amendment and which are used
but not defined herein shall have the meanings given them in the Fourth
Amendment. The undersigned, Paul F. Brereton, does hereby certify that he has
made a thorough inquiry into all matters certified herein and, based upon such
inquiry, experience, and the advice of counsel, does hereby further certify
that:

         1.       He is the duly elected, qualified, and acting Vice
                  President-Finance of Northstar.

         2.       All representations and warranties made by any Restricted
                  Person in any Canadian Loan Document delivered on or before
                  the date hereof are true on and as of the date hereof (except
                  to the extent that the facts upon which such representations
                  are based have been changed by the transactions contemplated
                  in the Fourth Amendment) as if such representations and
                  warranties had been made as of the date hereof.

         3.       No Default exists on the date hereof.

         4.       Each Restricted Person has performed and complied with all
                  agreements and conditions required in the Canadian Loan
                  Documents to be performed or complied with by it on or prior
                  to the date hereof.

         IN WITNESS WHEREOF, this instrument is executed by the undersigned as
of August 13, 2001.



                                             NORTHSTAR ENERGY CORPORATION



                                             By: /s/  Paul F. Brereton
                                                --------------------------------
                                                      Paul F. Brereton
                                                      Vice President-Finance
<PAGE>
                            ASSIGNMENT AND ACCEPTANCE
                           (Canadian Credit Agreement)


         Reference is made to the Canadian Credit Agreement dated as of August
29, 2000 (as amended, supplemented or otherwise modified from time to time, the
"Credit Agreement") among Northstar Energy Corporation, an Alberta corporation
(the "Canadian Borrower"), the Canadian Lenders (as defined in the Credit
Agreement) and Bank of America Canada, individually and as administrative agent
for the Lenders (the "Canadian Agent"). Terms defined in the Credit Agreement
are used herein with the same meaning.

         Each of the "Assignors" and the "Assignees" referred to on Schedule 1
agree as follows:

         1. Each Assignor hereby sells and assigns to the Assignees the portion
of its Canadian Maximum Credit Amount specified opposite its name on Schedule 1
hereto and the related Canadian Rights and Obligations (as hereinafter defined),
without recourse and without representation or warranty except as expressly set
forth herein, and each Assignee hereby purchases and assumes from the Assignors
the portion of the Canadian Maximum Credit Amount specified opposite its name on
Schedule 1 hereto and the related Canadian Rights and Obligations. After giving
effect to such sale and assignment, each Assignor's Canadian Maximum Credit
Amount and the amount of Canadian Loans owing to each Assignor will be as set
forth on Schedule 1 and each Assignee's Canadian Maximum Credit Amount and the
amount of Canadian Loans owing to each Assignee will be as set forth on Schedule
1. As used herein, "Canadian Rights and Obligations" means all outstanding
rights and obligations under the Credit Agreement and the other Canadian Loan
Documents relating to the Canadian Loans and the Canadian Maximum Credit Amount.
This Assignment and Acceptance is subject to Section 1.12 of the Credit
Agreement. On the Effective Date under such Section 1.12, the amount allocated
to the Canadian Maximum Credit Amount is $275,000,000 and the amount allocated
to the Tranche B Maximum Credit Amount is $525,000,000.

         2. Each Assignor (i) represents and warrants that it is the legal and
beneficial owner of the interest being assigned by it hereunder and that such
interest is free and clear of any adverse claim; (ii) makes no representation or
warranty and assumes no responsibility with respect to any statements,
warranties or representations made in or in connection with the Canadian Loan
Documents or the execution, legality, validity, enforceability, genuineness,
sufficiency or value of the Canadian Loan Documents or any other instrument or
document furnished pursuant thereto; (iii) makes no representation or warranty
and assumes no responsibility with respect to the financial condition of any
Restricted Person or the performance or observance by any Restricted Person of
any of its obligations under the Canadian Loan Documents or any other instrument
or document furnished pursuant thereto; and (iv) is delivering to Canadian Agent
its Canadian Note and requests that Canadian Agent exchange such Canadian Note
for a new Canadian Note payable to the order of such Assignor in an amount equal
to the Canadian Maximum Credit Amount retained by such Assignor as specified on
Schedule 1 and a new Canadian Note payable to the order of the relevant Assignee
in an amount equal to the Canadian Maximum Credit Amount of such Assignee
specified in Schedule 1.


<PAGE>

         3. Each Assignee (i) confirms that it has received a copy of the Credit
Agreement, together with copies of the financial statements referred to in
Section 6.2 thereof and such other documents and information as it has deemed
appropriate to make its own credit analysis and decision to enter into this
Assignment and Acceptance; (ii) agrees that it will, independently and without
reliance upon Canadian Agent, the Assignors or any other Lender and based on
such documents and information as it shall deem appropriate at the time,
continue to make its own credit decisions in taking or not taking action under
the Credit Agreement; (iii) confirms that it is an Eligible Transferee; (iv)
appoints and authorizes Canadian Agent to take such action as Canadian Agent on
its behalf and to exercise such powers and discretion under the Credit Agreement
as are delegated to Canadian Agent by the terms thereof, together with such
powers and discretion as are reasonably incidental thereto; (v) agrees that it
will perform in accordance with their terms all of the obligations that by the
terms of the Credit Agreement are required to be performed by it as a Lender.

         4. Following the execution of this Assignment and Acceptance, it will
be delivered to Canadian Agent for acceptance and recording by Canadian Agent.
The effective date for this Assignment and Acceptance (the "Effective Date")
shall be August 9, 2001.

         5. Upon such acceptance and recording by Canadian Agent, as of the
Effective Date, (i) the Assignees shall be parties to the Credit Agreement and,
to the extent provided in this Assignment and Acceptance, have the rights and
obligations of Canadian Lenders thereunder and (ii) the Assignors shall, to the
extent provided in this Assignment and Acceptance, relinquish their rights and
be released from their obligations under the Credit Agreement.

         6. Upon such acceptance and recording by Canadian Agent, from and after
the Effective Date, Canadian Agent shall make all payments under the Credit
Agreement and the Canadian Notes in respect of the interest assigned hereby
(including, without limitation, all payments of principal, interest and
commitment fees with respect thereto) to the appropriate Assignees, except that
BAs outstanding on the Effective Date shall settle on the expiration date
thereof in accordance with the interests therein held by Assignors on the
Effective Date. The Assignors and Assignees shall make all appropriate
adjustments in payments under the Credit Agreement and the Canadian Notes for
periods prior to the Effective Date directly between themselves.

         7. This Assignment and Acceptance shall be governed by, and construed
in accordance with, the Laws of the Province of Alberta, Canada.

         8. This Assignment and Acceptance may be executed in any number of
counterparts and by different parties hereto in separate counterparts, each of
which when so executed shall be deemed to be an original and all of which taken
together shall constitute one and the same agreement. Delivery of an executed
counterpart of this Assignment and Acceptance by telecopier shall be effective
as delivery of a manually executed counterpart of this Assignment and
Acceptance.

<PAGE>

         IN WITNESS WHEREOF, the Assignors and the Assignees have caused this
Assignment and Acceptance to be executed by their officers thereunto duly
authorized as of August 9, 2001.



ASSIGNORS:                       BANK OF AMERICA CANADA, as Assignor



                                 By:    /s/  Nelson Lam
                                        ----------------------------------------
                                        Name:      Nelson Lam
                                        Title:     Vice President


                                 ABN AMRO BANK CANADA, as Assignor


                                 By:    /s/  Mark Bohn
                                        ----------------------------------------
                                        Name:      Mark Bohn
                                        Title:     Group Vice President

                                 By:    /s/  Teresa Wu
                                        ----------------------------------------
                                        Name:      Teresa Wu
                                        Title:     Vice President


                                 BANK ONE, NA, CANADA BRANCH,
                                 as Assignor


                                 By:    /s/  Ronald L. Dierker
                                        ----------------------------------------
                                        Name:      Ronald L. Dierker
                                        Title:     Director, Capital Markets


                                 CITIBANK CANADA, as Assignor


                                 By:    /s/  James K. G. Campbell
                                        ----------------------------------------
                                        Name:      James K. G. Campbell
                                        Title:     Vice President


                           Assignment and Acceptance (Canadian Credit Agreement)
<PAGE>


                                 FIRST UNION NATIONAL BANK,
                                 as Assignor


                                 By:    /s/  David E. Humphreys
                                        ----------------------------------------
                                        Name:      David E. Humphreys
                                        Title:     Vice President


                                 SUNTRUST BANK, ATLANTA,
                                 as Assignor


                                 By:    /s/  David J. Edge
                                        ----------------------------------------
                                        Name:      David J. Edge
                                        Title:     Director


                                 THE CHASE MANHATTAN BANK,
                                 TORONTO BRANCH, as Assignor


                                 By:    /s/  Drew McDonald
                                        ----------------------------------------
                                        Name:      Drew McDonald
                                        Title:     Authorized Representative

                                 By:    /s/  Christine Chan
                                        ----------------------------------------
                                        Name:      Christine Chan
                                        Title:     Authorized Representative


                                 UMB BANK, as Assignor


                                 By:    /s/  Derek K. Duncan
                                        ----------------------------------------
                                        Name:      Derek K. Duncan
                                        Title:     Vice President


                           Assignment and Acceptance (Canadian Credit Agreement)
<PAGE>

                                 WESTDEUTSCHE LANDESBANK
                                 GIROZENTRALE, as Assignor


                                 By:    /s/  Salvatore Battinelli
                                        ----------------------------------------
                                        Name:      Salvatore Battinelli
                                        Title:     Managing Director

                                 By:    /s/  Walter T. Duffy III
                                        ----------------------------------------
                                        Name:      Walter T. Duffy III
                                        Title:     Associate Director





ASSIGNEES:                       BANCFIRST, as Assignee


                                 By:    /s/  Arthur B. Hobbs
                                        ----------------------------------------
                                        Name:      Arthur B. Hobbs
                                        Title:     Vice President


                                 BANK OF TOKYO - MITSUBISHI
                                 (CANADA), as Assignee


                                 By:    /s/  Davis J. Stewart
                                        ----------------------------------------
                                        Name:      Davis J. Stewart
                                        Title:     Vice President


                           Assignment and Acceptance (Canadian Credit Agreement)
<PAGE>


                                  BAYERISCHE LANDESBANK
                                  GIROZENTRALE, TORONTO  BRANCH,
                                  as Assignee


                                  By:    /s/  Eckhart Mehler
                                         ---------------------------------------
                                         Name:      Eckhart Mehler
                                         Title:     Senior Vice President &
                                                    Principal Officer

                                  By:    /s/  Bernd Erpenbeck
                                         ---------------------------------------
                                         Name:      Bernd Erpenbeck
                                         Title:     Second Vice President


                                  CANADIAN IMPERIAL BANK OF
                                  COMMERCE, as Assignee


                                  By:    /s/  Joelle Schellenberg
                                         ---------------------------------------
                                         Name:      Joelle Schellenberg
                                         Title:     Director


                                  CREDIT LYONNAIS NEW YORK
                                  BRANCH, as Assignee


                                  By:    /s/  Philippe Soustra
                                         ---------------------------------------
                                         Name:      Philippe Soustra
                                         Title:     Executive Vice President


                                  CREDIT SUISSE FIRST BOSTON,
                                  as Assignee


                                  By:    /s/  Peter Chauvin
                                         ---------------------------------------
                                         Name:      Peter Chauvin
                                         Title:     Vice President

                                  By:    /s/  Bill McFarland
                                         ---------------------------------------
                                         Name:      Bill McFarland
                                         Title:     Vice President


                           Assignment and Acceptance (Canadian Credit Agreement)
<PAGE>


                                  DEUTSCHE BANK AG NEW YORK
                                  BRANCH AND/OR CAYMAN ISLANDS
                                  BRANCH, as Assignee


                                  By:    /s/  Michael E. Keating
                                         ---------------------------------------
                                         Name:   Michael E. Keating
                                         Title:  Managing Director

                                  By:    /s/  Joel Makowsky
                                         ---------------------------------------
                                         Name:   Joel Makowsky
                                         Title:  Vice President


                                  ROYAL BANK OF CANADA, as Assignee


                                  By:    /s/  Lorne Gartner
                                         ---------------------------------------
                                         Name:   Lorne Gartner
                                         Title:  Vice President


                                  THE BANK OF NEW YORK, as Assignee


                                  By:    /s/  Raymond J. Palmer
                                         ---------------------------------------
                                         Name:   Raymond J. Palmer
                                         Title:  Vice President


                                  THE FUJI BANK, LIMITED, as Assignee


                                  By:    /s/  Jacques Azagury
                                         ---------------------------------------
                                         Name:   Jacques Azagury
                                         Title:  Senior Vice President & Manager


                           Assignment and Acceptance (Canadian Credit Agreement)
<PAGE>


                                  UBS AG, STAMFORD BRANCH,
                                  as Assignee


                                  By:    /s/  Wilfred V. Saint
                                         ---------------------------------------
                                         Name:      Wilfred S. Saint
                                         Title:     Associate Director
                                                    Banking Products Services US

                                  By:    /s/  Patricia O'Kicki
                                         ---------------------------------------
                                         Name:      Patricia O'Kicki
                                         Title:     Director
                                                    Banking Products Services




ACCEPTED AND APPROVED,
as of the 9th day of August, 2001:

BANK OF AMERICA, CANADA



By: /s/  Nelson Lam
    ---------------------------------------
    Name:  Nelson Lam
    Title: Vice President



APPROVED as of the 9th day of August, 2001:

NORTHSTAR ENERGY CORPORATION



By: /s/  John Richels
    ---------------------------------------
    Name:  John Richels
    Title: Chief Executive Officer


                           Assignment and Acceptance (Canadian Credit Agreement)
<PAGE>


                                   SCHEDULE 1
                                       TO
                            ASSIGNMENT AND ACCEPTANCE
                           (CANADIAN CREDIT AGREEMENT)















                                                         Page 1 of Schedule 1 to
                           Assignment and Acceptance (Canadian Credit Agreement)

<PAGE>


<Table>
<Caption>
                                                                                                                MAXIMUM AGGREGATE
                                                    NEW CANADIAN CREDIT                        OUTSTANDING     COMMITMENT UNDER U.S.
                               AMOUNT OF CANADIAN      MAXIMUM AMOUNT      PERCENTAGE SHARE      CANADIAN      CREDIT AGREEMENT AND
                                 MAXIMUM CREDIT     AFTER ASSIGNMENT AND  UNDER THE CANADIAN    LOANS AFTER       CANADIAN CREDIT
                                 AMOUNT ASSIGNED    CANADIAN NOTE AMOUNT   CREDIT AGREEMENT      ASSIGNMENT          AGREEMENT
          BANK NAME             (IN US DOLLARS)      (IN U.S. DOLLARS)     AFTER ASSIGNMENT   (IN US DOLLARS)    (IN U.S. DOLLARS)
          ---------            ------------------   --------------------  ------------------  ---------------  ---------------------
<S>                            <C>                  <C>                   <C>                 <C>              <C>
 ASSIGNORS:

 Bank of America Canada            5,156,250              28,125,000            7.500%          5,897,853.46       60,000,000.00

 ABN AMRO Bank Canada              3,750,000              23,437,500            6.250%          4,914,877.89       50,000,000.00

 Bank One, NA, Canada Branch       5,156,250              28,125,000            7.500%          5,897,853.46       60,000,000.00

 Citibank Canada                   3,750,000              23,437,500            6.250%          4,914,877.89       50,000,000.00

 First Union National Bank         5,156,250              28,125,000            7.500%          5,897,853.46       60,000,000.00

 SunTrust Bank                     1,562,500               7,031,250            1.875%          1,474,463.37       15,000,000.00

 The Chase Manhattan Bank,        20,625,000              28,125,000            7.500%          5,897,853.46       60,000,000.00
 Toronto Branch

 UMB Bank                            468,750               7,031,250            1.875%          1,474,463.37       15,000,000.00

 Westdeutsche Landesbank          20,625,000                       0                0                      0                   0
</Table>


                                                         Page 2 of Schedule 1 to
                           Assignment and Acceptance (Canadian Credit Agreement)

<PAGE>

<Table>
<Caption>
                                                                                                                MAXIMUM AGGREGATE
                                                    NEW CANADIAN CREDIT                        OUTSTANDING     COMMITMENT UNDER U.S.
                               AMOUNT OF CANADIAN      MAXIMUM AMOUNT      PERCENTAGE SHARE      CANADIAN      CREDIT AGREEMENT AND
                                 MAXIMUM CREDIT     AFTER ASSIGNMENT AND  UNDER THE CANADIAN    LOANS AFTER       CANADIAN CREDIT
                                 AMOUNT ASSIGNED    CANADIAN NOTE AMOUNT   CREDIT AGREEMENT      ASSIGNMENT          AGREEMENT
          BANK NAME             (IN US DOLLARS)      (IN U.S. DOLLARS)     AFTER ASSIGNMENT   (IN US DOLLARS)    (IN U.S. DOLLARS)
          ---------            ------------------   --------------------  ------------------  ---------------  ---------------------
<S>                            <C>                  <C>                   <C>                 <C>              <C>
ASSIGNEES:

BancFirst                            4,687,500            4,687,500            1.250%             982,463.37        10,000,000.00

Bank of Tokyo - Mitsubishi           7,968,750           18,750,000            5.000%           3,931,902.31        40,000,000.00
Canada

Bayerische                             937,500           18,750,000            5.000%           3,931,902.31        40,000,000.00
Landesbank
Girozentrale,
Toronto Branch

Canadian Imperial Bank of              937,500           11,718,750            3.125%           2,457,438.94        25,000,000.00
Commerce

Credit Lyonnais                        937,500           18,750,000            5.000%           3,931,902.31        40,000,000.00

Credit Suisse First Boston          23,437,500           23,437,500            6.250%           4,914,877.89        50,000,000.00

Deutsche Bank AG                     4,375,000           23,437,500            6.250%           4,914,877.89        50,000,000.00

Royal Bank of Canada                 7,500,000           28,125,000            7.500%           5,897,853.46        60,000,000.00

The Bank of New York                   468,750           21,093,750            5.625%           4,423,390.10        45,000,000.00

The Fuji Bank, Limited               3,281,250           21,093,750            5.625%           4,423,390.10        45,000,000.00
(Mizuho)

UBS AG                              11,718,750           11,718,750            3.125%           2,457,438.94        25,000,000.00
</Table>


                                                         Page 3 of Schedule 1 to
                           Assignment and Acceptance (Canadian Credit Agreement)