<PAGE>   1
                                                                   EXHIBIT 10.18

                     [ALBERTA TREASURY BRANCHES LETTERHEAD]





April 24, 2001


Geocan Energy Inc.
800, 717 -- 7 Avenue SW
Calgary, AB
T2P 0Z3



Attn:    Wayne Wadley, President


Dear Sir:

We have completed our review of your credit facilities described in our
Commitment Letter dated September 13, 2000. We are pleased to continue those
credit facilities on the same terms subject to amendments in the Schedule of
Changes attached. All securities we presently hold will continue in full force
and effect.

If this offer is acceptable please return the enclosed duplicate of this letter,
signed as indicated below, by 4 p.m. on May 8, 2001. If you have any questions,
or concerns, please contact us.

We look forward to our continued business relationship.



Yours truly,                                          Yours truly,




/s/ PHIL BURNHAM                                      /s/ BRAD HAACK
Phil Burnham                                          Brad Haack
Relationship Manager                                  Account Manager
/fg



Encl.

Accepted this 24 day of April, 2001



GEOCAN ENERGY INC.



PER: /s/ [ILLEGIBLE]
    ---------------------------


PER: /s/ [ILLEGIBLE]
    ---------------------------


<PAGE>   2



                               SCHEDULE OF CHANGES





         Attached to letter dated September 30, 2001.

         Terms used or defined in the Outline of Credit will have the same
meaning when used here.


A)       DETAILS OF CREDIT FACILITIES:

         Revolving Production Loan Facility - $2,500,000.00

         1.       Increase in funds to be used for the general operating
                  purposes of Borrower which includes the acquisition of oil and
                  gas properties and the development of oil and gas properties.

                  I.       advances will be limited to the least of:

                           a)       the maximum principal of the loan facility;

                           b)       the Borrowing Base;

                                    the "Borrowing Base" means that amount which
                                    is determined by Lender from time to time,
                                    after assessing the economic evaluation
                                    report prepared by or audited by a Lender
                                    approved consulting engineer on the
                                    Borrower's total proved reserves using the
                                    Lender's current evaluation guidelines and
                                    oil and gas price forecasts.

         2.       an amount, as determined by Lender, without restriction, that
                  would otherwise be capable of being repaid within the one-half
                  life of the total proved economic reserves of the Borrower.

         3.       if requested by Borrower and approved by Lender, advances may
                  be made available in any combination of the following.

                  a)       direct borrowings by way of Demand Promissory Note
                           with interest calculated on daily outstanding
                           principal at 1.5% above Prime will be payable on the
                           last day of each month with principal advances and
                           repayments to be in the minimum sum of $25,000 or
                           multiple of it;

                  b)       Letters of Credit and/or Letters of Guarantee, for
                           terms not to exceed one (1) year, to an aggregate
                           maximum of $250,000 outstanding at any one time, and
                           Borrower will be assessed a fee of 2.0% with a
                           minimum fee of $200 plus out of pocket expenses.

                  c)       Corporate MasterCard to a maximum of $25,000.00

         4.       Loans may be repaid in whole or in part at any time, without
                  penalty.

         5.       This line of credit is subject to review, at least annually.
                  The next annual review date has been established as July 31,
                  2001 but may be changed at the sole discretion of the Lender.




<PAGE>   3



                               SCHEDULE OF CHANGES


B.       ADDITIONAL SECURITY DOCUMENTS:


         All Securities presently held by lender will continue in effect for all
         Credit Facilities.

         The Security Documents (whether now held or hereafter delivered) will
         secure all Credit Facilities unless and until otherwise agreed in
         writing by Lender.


         The following additional security is required:

                  a)       Solicitor prepared Supplemental Debenture to be drawn
                           in the amount of $5,000,000 at Prime plus 2.0%
                           providing a floating charge over all undertaking of
                           the corporation

                  b)       Revolving Line of Credit Agreement together with
                           supporting Promissory Note in the amount of
                           $2,500,000 priced at 1.5% above Prime in $25,000
                           multiples;

                  c)       Group Creditor's Life Insurance - application or
                           waiver;

                  d)       All other security deemed necessary by ATB or it's
                           solicitor


C.       ADDITIONAL FEE:

         1.)      Non-refundable commitment fee of $2,000 is payable on
                  acceptance of this offer


Acceptance of this offer will authorize Lender to prepare any additional
security documents and proceed with related matter.



<PAGE>   4



Principal Sum:  $2,500,000.00                               Date: April 24, 2001


For value received the undersigned (jointly and severally, if more than one)
promises to pay to Alberta Treasury Branches ("ATB") at 239 - 8 Avenue SW
Calgary, Alberta, in lawful money of Canada, the Principal Sum
together with interest on all amounts of the Principal Sum remaining unpaid
from time to time after Date, both before and after default, at a variable rate
per annum of 1.5% above the Prime Lending Rate of ATB in effect from time to
time (the "Interest Rate"). Interest will be calculated daily and, prior to
demand, will be payable on the last day of each month. The Prime Lending Rate of
ATH in effect on this Date is ________ % per annum.




On this Date the Interest Rate is ____________%




                                      GEOCAN ENERGY INC.


                                       /s/ [ILLEGIBLE]
                                      ------------------------------------------
                                      Per:


                                       /s/ [ILLEGIBLE]
                                      ------------------------------------------
                                      Per:



<PAGE>   5



                       REVOLVING LINE OF CREDIT AGREEMENT


                      TO: Alberta Treasury Branches ("ATB")

                     239 - 8 Avenue SW, Calgary, AB T2P  1B9
                                (Branch Domicile)


                   RE: Revolving Line Of Credit (the "Credit")


                           Credit Limit $2,500,000.00


In consideration of ATB agreeing to provide the Credit to the undersigned on the
following terms, the undersigned (jointly and severally if more than one) agrees
as follows:

1.       ATB is authorized to advance or readvance (in either case, an
         "advance") funds under the Credit from time to time on a revolving
         basis by credit to account number 1131338-24 ("the Current Account") in
         the name of GEOCAN ENERGY INC. at the above branch.

         Each advance, if made, will be in the minimum amount of $25,000.00 (or
         such lesser sum as ATB may permit) or a multiple of it and will be made
         as required to meet directions to pay on or other withdrawals or
         payments from the Account.

2.       ATB may, without restriction:

         (a)      refuse to make any further advance on the Credit if the amount
                  of such advance, when added to the amount then outstanding on
                  the Credit, would exceed the Credit Limit; provided that this
                  agreement will apply to the Credit even if the amount advanced
                  or outstanding on it exceeds the Credit Limit;

         (b)      on oral or written notice to the undersigned, temporarily or
                  permanently reduce the Credit Limit; provided that, without
                  notice to the undersigned and for so long as ATB thinks fit,
                  ATB may reduce the Credit Limit by an amount equal to ATB's
                  liability (as determined by ATB) on Letters of Guarantee
                  issued by ATB at the request of the undersigned;

         (c)      on oral or written notice to the undersigned, terminate the
                  Credit, in which case no further advances will be available
                  and all amounts then outstanding on the Credit will become
                  immediately payable.

3.       ATB is authorized to debit the Account from time to time to pay
         interest, principal, costs, or other monies owing to ATB in respect of
         the Credit, provided that ATB will not be obliged to do so at any time.

4.       The undersigned promises to pay interest to ATB on the aggregate of all
         advances from time to time outstanding under the Credit at the rate(s)
         set out below. Interest in all cases will be calculated daily and,
         prior to demand, will be payable on the last day of each month. The
         interest rate applicable to the amount outstanding on the Credit at any
         time will be:

         (a)      as to the first $2,500,000, a variable rate per annum equal to
                  1.5% above the Prime Lending Rate of ATB; and

         (b)      as to the balance (if any), a variable rate per annum equal to
                  n/a% above the Prime Lending Rate of ATB.

         The undersigned will execute and deliver (or has executed and
         delivered) to ATB demand promissory note(s) (or promise(s) to pay) for
         (or totalling) the amount of the Credit Limit at the applicable
         interest rate(s), to be held at ATB as further evidence of and security
         for the obligation of the undersigned to pay to ATB ON DEMAND, the
         interest, principal, costs and other monies owing to ATB from time to
         time in respect to the Credit.

6.       ATB's written statement of the amount owing under the Credit and the
         interest rate(s) applicable to it at any particular time will, in the
         absence of obvious error, be conclusively binding on the undersigned
         for all purposes. Such statement may be included with the consolidated
         statement of the Account from time to time.

7.       It is understood that additional agreements may from time to time exist
         between ATB and the undersigned relating to the Credit and in the event
         of a conflict between this agreement and other agreement relating to
         the Credit such other agreement will prevail; if there is no conflict,
         this agreement and such other agreement will be read in conjunction
         with and as supplementary to each other.


The undersigned has executed this agreement this 24 day of April, 2001.


                                       GEOCAN ENERGY INC.


                                       /s/ [ILLEGIBLE]
                                       -----------------------------------------
                                       Per:


                                       /s/ [ILLEGIBLE]
                                       -----------------------------------------
                                       Per:

<PAGE>   6
                          FIRST SUPPLEMENTAL DEBENTURE


    THIS FIRST SUPPLEMENTAL DEBENTURE made as of the 27th day of April, 2001


BETWEEN:


                 GEOCAN ENERGY INC. (THE "CORPORATION"), having an office at
                 Calgary, Alberta

                                     - and -

                 ALBERTA TREASURY BRANCHES, with an office at Calgary, Alberta
                 ("Treasury Branches")



                 The Corporation issued to and in favour of Treasury Branches a
Floating Charge Demand Debenture dated November 18, 1998 (the "Principal
Debenture"), in which the Corporation, for value received, acknowledged itself
indebted and promised to pay on demand to Treasury Branches the Principal Sum of
TWO MILLION DOLLARS ($2,000,000.00) and interest thereon at an annual rate equal
to Two per cent (2.0%) above the Prime Lending Rate established from time to
time by Treasury Branches, calculated monthly.

                 The Corporation and Treasury Branches wish to amend the
Principal Debenture to Increase the Principal Sum of the Principal Debenture to
FIVE MILLION DOLLARS ($5,000,000.00).

                 For good and valuable consideration (the receipt and
sufficiency of which is hereby acknowledged) the parties agree as follows:

1.       The capitalized terms used in this First Supplemental Debenture,
         including the recitals, unless otherwise expressly provided shall have
         the respective meanings as are given to the same terms in the Principal
         Debenture.

2.       This First Supplemental Debenture and the Principal Debenture shall
         have effect, so far as practicable, as though all of the provisions
         hereof and thereof were contained in one instrument. Any reference in
         the Principal Debenture to itself shall be deemed to be a reference to
         the Principal Debenture as amended by this First Supplemental
         Debenture.

<PAGE>   7

                                       -2-

3.       The Principal Sum be increased from TWO MILLION DOLLARS ($2,000,000.00)
         to FIVE MILLION DOLLARS ($5,000,000.00).

4.       The Principal Debenture as amended and supplemented by this First
         Supplemental Debenture, and the grant, assignment, mortgage, pledge,
         charge and hypothec created and provided for in the Principal Debenture
         are in all respects confirmed, ratified and preserved.

5.       The First Supplemental Debenture shall be governed by and construed in
         accordance with the laws of the Province of Alberta and the laws of
         Canada applicable therein.

6.       Except as provided herein, the provisions of the Principal Debenture
         remain in full force and effect, unamended.

7.       The First Supplemental Debenture and everything herein contained will
         enure to the benefit of Treasury Branches and its successors and
         assigns, and be binding upon the Corporation and its successors and
         permitted assigns.

8.       The First Supplemental Debenture will not prejudice any rights which
         Treasury Branches may have under the Principal Debenture. It will not
         create any merger or alter or prejudice the rights of Treasury Branches
         as regards any other security held by Treasury Branches or as regards
         any surety or subsequent encumbrance of any person or company not a
         party hereto, liable to pay the amount of any indebtedness of the
         Corporation to Treasury Branches, or interested in the property, assets
         or undertaking of the Corporation, all of which rights are hereby
         preserved.

         IN WITNESS WHEREOF the parties hereto have executed and delivered this
First Supplemental Debenture as of the date first above written.



                                      GEOCAN ENERGY INC.


                                      Per: /s/ [ILLEGIBLE]
                                           -----------------------

                                      Per: /s/ WAYNE WEDLEY
                                           -----------------------

<PAGE>   8


                      SECOND PLEDGE AGREEMENT OF DEBENTURE

SECOND PLEDGE AGREEMENT made as of the 27 day of April, 2001

         GEOCAN ENERGY INC. (the "Corporation") having lodged and deposited with
the ALBERTA TREASURY BRANCHES (the "Treasury Branches") a Debenture of the
Corporation dated November 18, 1998 (the "Principal Debenture"), as amended and
supplemented by the First Supplemental Debenture made as of April 27, 2001 (the
Principal Debenture as amended and supplemented by the First Supplemental
Debenture made as of April 27, 2001 is called the "Debenture") payable to the
Treasury Branches in the Principal Amount of FIVE MILLION DOLLARS
($5,000,000.00) for valuable consideration, agrees with the Treasury Branches as
follows:

1.       The Debenture is hereby assigned, transferred, pledged and hypothecated
to and in favour of the Treasury Branches as general and continuing collateral
security for the payment and fulfilment of all debts, liabilities and
obligations, present and future, direct or indirect, matured or not, of the
Corporation to the Treasury Branches of whatsoever nature and kind and whether
arising from any agreement or dealings between the Treasury Branches and the
Corporation or from any agreement or dealings between the Treasury Branches and
any third party by which the Treasury Branches may be or become in any manner
whatsoever a creditor of the Corporation or howsoever otherwise arising and
whether the Corporation be bound alone or with another or others and whether as
principal or surety.

2.       If the security constituted by the Debenture shall become enforceable
in accordance with the terms thereof, then the Treasury Branches or its nominee
shall be entitled to sell at a public or private sale or otherwise realize upon
the security of the Debenture and to otherwise exercise and enforce all the
rights and remedies of a holder of the Debenture free from any control of the
Corporation; provided, however, the Treasury Branches shall not be bound to deal
with the Debenture in any way or to exercise any rights or remedies as aforesaid
and shall not be liable for any loss that may be occasioned by any failure to do
so.

3.       The Treasury Branches may grant extensions of time and other
indulgences, take and give up securities, accept compositions, grant releases
and discharges and otherwise deal with the Corporation and all other parties and
securities as the Treasury Branches may see fit, all without prejudice to the
debts, liabilities and obligations of the Corporation under the Debenture, or
the Treasury Branches's rights in respect of the Debenture and the security
thereby and hereby constituted.

4.       The Debenture and the security hereby constituted are in addition to
and not in substitution for any other security now or hereafter held by the
Treasury Branches and shall not operate as a merger of any simple contract debt
or suspend the fulfilment of, or affect the rights, remedies or powers of the
Treasury Branches in respect of any present or future debts, liabilities or
obligations of the Corporation to the Treasury Branches or any securities now
or hereafter held by the Treasury Branches for the payment or fulfilment
thereof.


<PAGE>   9


                                      -2-

5.       Payment by the Corporation to the Treasury Branches of interest for any
period in respect of the debts, liabilities and obligations of the Corporation
to the Treasury Branches shall be deemed to be payment in full satisfaction of
the interest payment for the same period provided for under the terms of the
Debenture.

6.       This Agreement shall be binding upon the Corporation and its successors
and assigns and shall enure to the benefit of the Treasury Branches and its
successors and assigns.

         The Corporation has caused this Agreement to be executed on the 27 day
of April, 2001.


                                      GEOCAN ENERGY, INC.


                                      Per: /s/ [ILLEGIBLE]
                                           -----------------------

                                      Per: /s/ WAYNE WEDLEY
                                           -----------------------