EXHIBIT 10.12

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CANADIAN $54,799,500

AMENDED AND RESTATED CREDIT AGREEMENT

dated as of May 24, 2002,

among

MARKWEST RESOURCES CANADA CORP.,
as the Borrower,

and

CERTAIN FINANCIAL INSTITUTIONS,
as the Lenders,

and

BANK OF AMERICA, N.A. [acting though its Canadian Branch]
as the Canadian Administrative Agent for the Lenders

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BANC OF AMERICA SECURITIES LLC,
as Lead Arranger and Sole Book Manager

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TABLE OF CONTENTS

|              |  |                                                                                 |  | Page
|------------- |  | ------------------------------------------------------------------------------- |  | ----
|ARTICLE I     |  | DEFINITIONS AND ACCOUNTING TERMS                                                |  | 1   
|SECTION 1.1   |  | Defined Terms                                                                   |  | 1   
|SECTION 1.2   |  | Use of Defined Terms                                                            |  | 18  
|SECTION 1.3   |  | Cross-References                                                                |  | 18  
|SECTION 1.4   |  | Accounting and Financial Determinations                                         |  | 18  
|ARTICLE II    |  | REVOLVING LOAN COMMITMENTS, BORROWING PROCEDURES AND NOTES                      |  | 19  
|SECTION 2.1   |  | Revolving Loan Commitments                                                      |  | 19  
|SECTION 2.1.1 |  | Revolving Loan Commitment                                                       |  | 19  
|SECTION 2.1.2 |  | Commitment to Issue Letters of Credit                                           |  | 19  
|SECTION 2.1.4 |  | [Intentionally Blank]                                                           |  | 20  
|SECTION 2.1.5 |  | Lenders Not Required To Make Loans or Issue or Participate in Letters of Credit |  | 20  
|SECTION 2.1.6 |  | Increase in Revolving Loan Commitment Amount                                    |  | 21  
|SECTION 2.2   |  | Optional Reduction of Revolving Loan Commitment Amount                          |  | 22  
|SECTION 2.3   |  | Borrowing Procedure                                                             |  | 22  
|SECTION 2.4   |  | Continuation and Conversion Elections                                           |  | 23  
|SECTION 2.5   |  | Notes                                                                           |  | 23  
|SECTION 2.6   |  | Letters of Credit                                                               |  | 23  
|SECTION 2.6.1 |  | Issuance Requests                                                               |  | 23  
|SECTION 2.6.2 |  | Issuances and Extensions                                                        |  | 24  
|SECTION 2.6.3 |  | Other Lenders= Participation                                                    |  | 24  
|SECTION 2.6.4 |  | Disbursements                                                                   |  | 25  
|SECTION 2.6.5 |  | Reimbursement                                                                   |  | 25  
|SECTION 2.6.6 |  | Deemed Disbursements                                                            |  | 25  
|SECTION 2.6.7 |  | Nature of Reimbursement Obligations                                             |  | 26  
|SECTION 2.6.8 |  | Increased Costs; Indemnity                                                      |  | 26  
|ARTICLE III   |  | REPAYMENTS, PREPAYMENTS, INTEREST AND FEES                                      |  | 27  
|SECTION 3.1   |  | Repayments and Prepayments                                                      |  | 27  
|SECTION 3.1.1 |  | Optional Prepayment                                                             |  | 27  
|SECTION 3.1.2 |  | Mandatory Prepayment                                                            |  | 27  
|SECTION 3.1.3 |  | Mandatory Prepayment on Acceleration                                            |  | 28  
|SECTION 3.2   |  | Interest Provisions                                                             |  | 28  
|SECTION 3.2.1 |  | Rates                                                                           |  | 28  
|SECTION 3.2.2 |  | Default Rate                                                                    |  | 28  
|SECTION 3.2.3 |  | Payment Dates                                                                   |  | 28  
|SECTION 3.2.4 |  | [Intentionally Blank]                                                           |  | 29  
|SECTION 3.3   |  | Fees                                                                            |  | 29  
|SECTION 3.3.1 |  | Commitment Fee                                                                  |  | 29  
|SECTION 3.3.2 |  | Canadian Administrative Agent=s Fee                                             |  | 29  
|SECTION 3.3.3 |  | Letter of Credit Fees                                                           |  | 29  
|ARTICLE IV    |  | CERTAIN LIBO RATE AND OTHER PROVISIONS                                          |  | 29  
|SECTION 4.1   |  | Fixed Rate Lending Unlawful                                                     |  | 29  
|SECTION 4.2   |  | Deposits Unavailable                                                            |  | 30  
|SECTION 4.3   |  | Increased LIBO Rate Loan Costs, etc.                                            |  | 30  
|SECTION 4.4   |  | Funding Losses                                                                  |  | 30  
|SECTION 4.5   |  | Increased Capital Costs                                                         |  | 30  
|SECTION 4.6   |  | Taxes                                                                           |  | 31  

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|SECTION 4.7    |  | Payments, Computations, etc.                         |  | 31
|-------------- |  | ---------------------------------------------------- |  | --
|SECTION 4.8    |  | Sharing of Payments                                  |  | 32
|SECTION 4.9    |  | Setoff                                               |  | 32
|SECTION 4.10.  |  | Currency Conversion and Currency Indemnity           |  | 32
|ARTICLE V      |  | CONDITIONS TO EFFECTIVENESS                          |  | 33
|SECTION 5.1    |  | Conditions to Effectiveness and Initial Borrowing    |  | 33
|SECTION 5.1.1  |  | Resolutions, etc.                                    |  | 33
|SECTION 5.1.2  |  | Delivery of this Agreement;                          |  | 34
|SECTION 5.1.3  |  | Guaranty Agreements                                  |  | 34
|SECTION 5.1.4  |  | Collateral Documents                                 |  | 34
|SECTION 5.1.5  |  | Closing Certificate                                  |  | 34
|SECTION 5.1.6  |  | Opinions of Counsel                                  |  | 34
|SECTION 5.1.7  |  | Closing Fees, Expenses, etc.                         |  | 34
|SECTION 5.1.8  |  | Evidence of Insurance                                |  | 34
|SECTION 5.1.9  |  | [Intentionally Blank]                                |  | 34
|SECTION 5.1.10 |  | Hedging Policy                                       |  | 34
|SECTION 5.1.11 |  | Other                                                |  | 35
|SECTION 5.2    |  | All Borrowings                                       |  | 35
|SECTION 5.2.1  |  | Compliance with Warranties, No Default, etc.         |  | 35
|SECTION 5.2.2  |  | Borrowing Request                                    |  | 35
|SECTION 5.2.3  |  | Satisfactory Legal Form                              |  | 35
|ARTICLE VI     |  | REPRESENTATIONS AND WARRANTIES                       |  | 36
|SECTION 6.1    |  | Organization, etc.                                   |  | 36
|SECTION 6.2    |  | Due Authorization, Non-Contravention, etc.           |  | 36
|SECTION 6.3    |  | Government Approval, Regulation, etc.                |  | 36
|SECTION 6.4    |  | Validity, etc.                                       |  | 36
|SECTION 6.5    |  | Financial Information                                |  | 36
|SECTION 6.6    |  | No Material Adverse Change                           |  | 37
|SECTION 6.7    |  | Litigation, Labor Controversies, etc.                |  | 37
|SECTION 6.8    |  | Subsidiaries                                         |  | 37
|SECTION 6.9    |  | Ownership of Properties                              |  | 37
|SECTION 6.10   |  | Taxes                                                |  | 37
|SECTION 6.11   |  | [Intentionally Blank]                                |  | 37
|SECTION 6.12   |  | Compliance with Law                                  |  | 37
|SECTION 6.13   |  | Claims and Liabilities                               |  | 37
|SECTION 6.14   |  | No Prohibition on Perfection of Collateral Documents |  | 37
|SECTION 6.15   |  | Solvency                                             |  | 38
|SECTION 6.16   |  | Environmental Warranties                             |  | 38
|SECTION 6.17   |  | Regulations T, U and X                               |  | 39
|SECTION 6.18   |  | Accuracy of Information                              |  | 39
|SECTION 6.19   |  | Default                                              |  | 39
|SECTION 6.20   |  | [Intentionally Blank]                                |  | 39
|SECTION 6.21   |  | Oil and Gas Reserves                                 |  | 39
|SECTION 6.22   |  | Title Opinion                                        |  | 39
|ARTICLE VII    |  | COVENANTS                                            |  | 40
|SECTION 7.1    |  | Affirmative Covenants                                |  | 40
|SECTION 7.1.1  |  | Financial Information, Reports, Notices, etc.        |  | 40
|SECTION 7.1.2  |  | Compliance with Laws, etc.                           |  | 42
|SECTION 7.1.3  |  | Maintenance of Properties                            |  | 42
|SECTION 7.1.4  |  | Use of Proceeds                                      |  | 42

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|SECTION 7.1.5  |  | Insurance                                                     |  | 42
|-------------- |  | ------------------------------------------------------------- |  | --
|SECTION 7.1.6  |  | Books and Records                                             |  | 43
|SECTION 7.1.7  |  | Environmental Covenant                                        |  | 43
|SECTION 7.1.8  |  | Further Assurances; Additional Collateral; Recording of Liens |  | 44
|SECTION 7.1.9  |  | Compliance with Hedging Policy; Hedging Agreements            |  | 45
|SECTION 7.1.10 |  | Hedging Agreements                                            |  | 45
|SECTION 7.1.11 |  | Performance of Obligations                                    |  | 45
|SECTION 7.1.12 |  | Payment of Taxes and Claims                                   |  | 45
|SECTION 7.2    |  | Negative Covenants                                            |  | 46
|SECTION 7.2.1  |  | Business Activities; Changes In Hedging Policy                |  | 46
|SECTION 7.2.2  |  | Indebtedness                                                  |  | 46
|SECTION 7.2.3  |  | Liens                                                         |  | 47
|SECTION 7.2.4  |  | Financial Covenants                                           |  | 49
|SECTION 7.2.5  |  | Investments                                                   |  | 49
|SECTION 7.2.6  |  | Restricted Payments, etc.                                     |  | 49
|SECTION 7.2.7  |  | Rental Obligations                                            |  | 50
|SECTION 7.2.8  |  | Consolidation, Merger, etc.                                   |  | 50
|SECTION 7.2.9  |  | Asset Dispositions, etc.                                      |  | 50
|SECTION 7.2.10 |  | Subordinated Debt Documents                                   |  | 51
|SECTION 7.2.11 |  | Transactions with Affiliates                                  |  | 51
|SECTION 7.2.12 |  | Negative Pledges, Restrictive Agreements, etc.                |  | 51
|SECTION 7.2.13 |  | Limitation On Hedging Agreements                              |  | 52
|SECTION 7.2.14 |  | Use of Proceeds                                               |  | 52
|SECTION 7.2.15 |  | Gas Imbalances, Take-or-Pay or Other Prepayments              |  | 52
|ARTICLE VIII   |  | EVENTS OF DEFAULT                                             |  | 52
|SECTION 8.1    |  | Listing of Events of Default                                  |  | 52
|SECTION 8.1.1  |  | Non-Payment of Obligations                                    |  | 52
|SECTION 8.1.2  |  | Breach of Warranty                                            |  | 52
|SECTION 8.1.3  |  | Non-Performance of Certain Covenants and Obligations          |  | 53
|SECTION 8.1.4  |  | Non-Performance of Other Covenants and Obligations            |  | 53
|SECTION 8.1.5  |  | Default Under Other Indebtedness or U.S. Credit Agreement     |  | 53
|SECTION 8.1.6  |  | Judgments                                                     |  | 53
|SECTION 8.1.7  |  | Default under Parent Guaranty                                 |  | 53
|SECTION 8.1.8  |  | Control of the Borrower                                       |  | 53
|SECTION 8.1.9  |  | Bankruptcy, Insolvency, etc.                                  |  | 53
|SECTION 8.1.10 |  | Impairment of Security, etc.                                  |  | 54
|SECTION 8.1.11 |  | Default Under Material Agreement                              |  | 54
|SECTION 8.1.12 |  | Invalidity of Loan Documents                                  |  | 54
|SECTION 8.2    |  | Action if Bankruptcy                                          |  | 54
|SECTION 8.3    |  | Action if Other Event of Default                              |  | 54
|ARTICLE IX     |  | THE AGENT                                                     |  | 55
|SECTION 9.1    |  | Actions                                                       |  | 55
|SECTION 9.2    |  | Funding Reliance, etc.                                        |  | 55
|SECTION 9.3    |  | Exculpation                                                   |  | 56
|SECTION 9.4    |  | Successor                                                     |  | 56
|SECTION 9.5    |  | Loans by Bank of America, N.A                                 |  | 57
|SECTION 9.6    |  | Credit Decisions                                              |  | 57
|SECTION 9.7    |  | Copies, etc.                                                  |  | 57
|SECTION 9.8    |  | Default; Collateral                                           |  | 57
|SECTION 9.9    |  | Lender Hedging Agreements                                     |  | 58

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|ARTICLE X     |  | MISCELLANEOUS PROVISIONS                                                          |  | 59
|------------- |  | --------------------------------------------------------------------------------- |  | --
|SECTION 10.1  |  | Waivers, Amendments, Release of Collateral, etc.                                  |  | 59
|SECTION 10.2  |  | Notices                                                                           |  | 60
|SECTION 10.3  |  | Payment of Costs and Expenses                                                     |  | 60
|SECTION 10.4  |  | Indemnification                                                                   |  | 61
|SECTION 10.5  |  | Survival                                                                          |  | 61
|SECTION 10.6  |  | Severability                                                                      |  | 61
|SECTION 10.7  |  | Headings                                                                          |  | 62
|SECTION 10.8  |  | Execution in Counterparts                                                         |  | 62
|SECTION 10.9  |  | Governing Law; Submission to Process                                              |  | 62
|SECTION 10.10 |  | Successors and Assigns                                                            |  | 62
|SECTION 10.11 |  | Other Transactions                                                                |  | 64
|SECTION 10.12 |  | Forum Selection and Consent to Jurisdiction                                       |  | 64
|SECTION 10.13 |  | Waiver of Jury Trial                                                              |  | 64
|SECTION 10.14 |  | Confidentiality                                                                   |  | 65
|SECTION 10.15 |  | [Intentionally Blank]                                                             |  | 65
|SECTION 10.16 |  | Priority of Hedging Obligations                                                   |  | 65
|SECTION 10.17 |  | Certain Remedies                                                                  |  | 65
|SECTION 10.18 |  | Maximum Rate                                                                      |  | 65
|SECTION 10.19 |  | Entire Agreement                                                                  |  | 66
|SECTION 10.20 |  | Annual Rates of Interest                                                          |  | 66
|SECTION 10.21 |  | Waiver of Judgment Interest Act (Alberta                                          |  | 66
|SECTION 10.22 |  | Deemed Reinvestment Not Applicable                                                |  | 66
|SECTION 10.23 |  | Consent and Ratification of Collateral Documents                                  |  | 67
|SECTION 10.24 |  | Assignment                                                                        |  | 67
|SECTION 10.25 |  | Intercreditor Agreement; Agreement Regarding Collateral                           |  | 67
|SECTION 10.26 |  | Transfer of Assets to the MLP and Release of Liens and Guaranties Related Thereto |  | 67

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|SCHEDULES:      |  |   |  |                                                     
|--------------- |  | - |  | ----------------------------------------------------
|Schedule 1.1(a) |  |   |  | Disclosure Schedule                                 
|Schedule 1.1(b) |  |   |  | Lender Revolving Loan Commitments                   
|Schedule 5.1.4  |  |   |  | Collateral Documents to Be Delivered                
|Schedule 7.1.9  |  |   |  | Canadian Hedge Agreements                           
|Schedule 10.23  |  |   |  | Existing Collateral Documents                       
|EXHIBITS:       |  |   |  |                                                     
|Exhibit A       |  |  |  | Form of Note                                        
|Exhibit B       |  |  |  | Form of Borrowing Request                           
|Exhibit C       |  |  |  | Form of Continuation/Conversion Notice              
|Exhibit D       |  |  |  | Form of Lender Assignment Agreement                 
|Exhibit E-1     |  |  |  | Form of Legal Opinion of Davis, Graham & Stubbs LLP 
|Exhibit E-2     |  |  |  | Form of Legal Opinion of Fraser Milner Casgrain LLP 
|Exhibit E-3     |  |  |  | Form of Legal Opinion of Barry Spector              
|Exhibit F       |  |  |  | Form of Compliance Certificate                      
|Exhibit G-1     |  |  |  | Form of Parent Guaranty                             
|Exhibit G-2     |  |  |  | Form of Canadian Company Guaranty                   
|Exhibit H-1     |  |  |  | Form of General Security Agreement                  
|Exhibit H-2     |  |  |  | Form of Security Pledge Agreement                   
|Exhibit H-3     |  |  |  | Form of Amended and Restated Fixed Charge Mortgage  
|Exhibit I-      |  |  |  | Form of Issuance Request                            
|Exhibit J       |  |  |  | Form of Amended and Restated Intercreditor Agreement
|Exhibit K       |  |  |  | Form of Agreement Regarding Collateral              

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AMENDED AND RESTATED CREDIT AGREEMENT

THIS AMENDED AND RESTATED CREDIT AGREEMENT dated as of May 24, 2002, among MARKWEST RESOURCES CANADA CORP., an Alberta corporation (the
"Borrower"), the various financial institutions as are or may become parties hereto (collectively, the
"Lenders"), and BANK OF AMERICA, N.A. [acting through its Canadian Branch] ("BofA
Canada"), as Canadian administrative agent for the Lenders (in such capacity, the "Canadian Administrative Agent").

W I T N E S S E T H:

WHEREAS, the Borrower is engaged in the business of oil and gas exploration, production and development and activities related or ancillary thereto, natural gas,
natural gas liquid and crude oil marketing, and the acquisition, ownership, operation, leasing and construction of natural gas processing and treating plants, fractionation facilities and pipelines,
and natural gas, natural gas liquids and crude oil storage, transportation and terminalling, and activities related or ancillary to the foregoing;

WHEREAS,
pursuant to that certain Credit Agreement dated as of October 12, 2001 as amended by First Amendment to Credit Agreement dated (the "First
Amendment) dated as of March 29, 2002 (the "Existing Credit Agreement"), among Borrower, certain financial institutions
(the "Existing Lenders") and the Administrative Agent, the Existing Lenders agreed to make revolving loans (the "Existing
Loans") and Bank of America, N.A. as issuer agreed to issue letters of credit;

WHEREAS,
concurrently herewith, MarkWest Hydrocarbon, Inc., a Delaware corporation (the "Parent"), certain financial institutions
(the "U.S. Lenders") and Bank of America, N.A., as Administrative Agent, are entering into that certain U.S. Credit Agreement (defined below), pursuant
to which the U.S. Lenders agree to make loans in an amount up to U.S. $25,000,000;

WHEREAS,
concurrently herewith, certain lenders (the "MarkWest OLLC Lenders"), are providing financing to MarkWest OLLC (as defined
herein) pursuant to that certain MarkWest OLLC Credit Agreement (as defined herein);

WHEREAS,
in order to, among other things (i) take into account certain aspects of the MarkWest OLLC Credit Agreement, and (ii) to incorporate the amendments made to the
Existing Credit Agreement by the First Amendment, the Borrower, the Lenders, and the Administrative Agent hereby
make further amendments to the Existing Credit Agreement and restate the Existing Credit Agreement, as amended by the First Amendment; and

WHEREAS,
upon and subject to the terms and conditions of this Agreement, the Lenders are willing to extend such credit to the Borrower.

NOW,
THEREFORE, the parties hereto agree as follows:

ARTICLE I
DEFINITIONS AND ACCOUNTING TERMS

SECTION
1.1Defined Terms.    The following terms (whether or not underscored) when used in this Agreement,
including its preamble and recitals, shall, except where the context otherwise requires, have the following meanings (such meanings to be equally applicable to the singular and plural forms thereof):

"Acquisition" means any transaction or series of related transactions for the purpose of or resulting, directly or indirectly, in
(a) the acquisition of all or substantially all of the assets of a Person, or of any business or division of a Person, (b) the acquisition of in excess of 50% of the capital stock,
partnership interests, membership interests or equity of any Person, or otherwise causing any Person to become a Subsidiary, or (c) an amalgamation, merger or consolidation or any other
combination of the Borrower or a Subsidiary with another Person (other than a Person that is a Subsidiary).

"Administrative Agent" means Bank of America, N.A., in its capacity as agent for the Lenders appointed pursuant to Section 9.1, to act in accordance with the terms
of this Agreement and the

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Intercreditor Agreement, and includes each other Person as shall have subsequently been appointed as the successor Administrative Agent pursuant to Section 9.4.

"Administrative Questionnaire" means an Administrative Details Form in a form supplied by the Administrative Agent.

"Affiliate" of any Person means any other Person which, directly or indirectly, controls, is controlled by or is under common control with
such Person. A Person shall be deemed to be "controlled by" any other Person if such other Person possesses, directly or indirectly, power (a) to vote 10% or more of the securities (on a fully
diluted basis) having ordinary voting power for the election of directors or managing general partners; or (b) to direct or cause the direction of the management and policies of such Person
whether by contract or otherwise.

"Agent" means each of the Canadian Administrative Agent and the Administrative Agent, and
"Agents" means the Canadian Administrative Agent and the Administrative Agent, collectively.

"Agreement" means, on any date, this Amended and Restated Credit Agreement as originally in effect on the Effective Date and as thereafter
from time to time amended, supplemented, amended and restated, or otherwise modified and in effect on such date.

"Agreement Regarding Collateral" means the Agreement Regarding Collateral dated as of even date herewith substantially in the form
attached hereto asExhibit K, as amended, supplemented, restated or otherwise modified from time to time.

"Appalachia" means MarkWest Energy Appalachia, L.L.C., a Delaware limited liability company.

"Applicable Margin" means, with respect to any Loan of any type or any Letter of Credit, and at such time as the Leverage Ratio is in one
of the following ranges, the number of basis points ("b.p.")per annumfor the relevant type of Loan,
Commitment Fee or Letter of Credit and the relevant range set forth below:

|Pricing
Level |  | Leverage Ratio                                      |  | Applicable Margin:
LIBO Rate Loan |  | Letter of
Credit |  | Applicable
Margin:
Canadian
Prime Rate
Loan |  | Commitment Fee
|------------- |  | --------------------------------------------------- |  | --------------------------------- |  | ---------------- |  | ------------------------------------------- |  | --------------
|1             |  | Less than or equal to 1.0X                          |  | 175.0 b.p.                        |  | 175.0 b.p.       |  | 37.5 b.p.                                   |  | 25.0 b.p.     
|2             |  | Greater than 1.0X, but less than or equal to 2.0X   |  | 200.0 b.p.                        |  | 200.0 b.p.       |  | 62.5 b.p.                                   |  | 30.0 b.p.     
|3             |  | Greater than 2.0X, but less than or equal to 2.75X  |  | 225.0 b.p.                        |  | 225.0 b.p.       |  | 87.5 b.p.                                   |  | 37.5 b.p.     
|4             |  | Greater than 2.75X, but less than or equal to 3.25X |  | 250.0 b.p.                        |  | 250.0 b.p.       |  | 112.5 b.p.                                  |  | 50.0 b.p.     
|5             |  | Greater than 3.25X                                  |  | 275.0 b.p.                        |  | 275.0 b.p.       |  | 137.5 b.p.                                  |  | 50.0 b.p.     

The
Leverage Ratio shall be determined from the then most recent quarterly financial statements delivered by the Borrower pursuant to Section 7.1.1and any changes in Applicable Margin shall become
effective the first day of the third month following the date such financial
statements are dated. In the event that the Borrower shall at any time fail to furnish the Lenders such financial statements required to be delivered under Section 7.1.1, the maximum Applicable
Margin and Commitment Fee as set forth above shall apply until such time as such financial statements are
so delivered. Changes in the
Applicable Margin and Commitment Fee as a result of a change in the Leverage Ratio will occur automatically as aforesaid without notice.

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The
Applicable Margin shall be set at Pricing Level 4 for the period beginning on the Effective Date and ending on June 30, 2002, unless during such period the Leverage Ratio
falls within Pricing Level 5, in which case Pricing Level 5 will apply.

"Approved Fund" means any Fund that is administered or managed by (a) a Lender, (b) an Affiliate of a Lender or
(c) an entity or an Affiliate of an entity that administers or manages a Lender.

"Assignment and Assumption" means an assignment and assumption entered into by a Lender and an Eligible Assignee (with the consent of any
party whose consent is required bySection 10.10), and accepted by the Administrative Agent, in substantially the form of Exhibit D.

"Authorized Officer" means, relative to any Obligor, those of its officers whose signatures and incumbency shall have been certified to
the Canadian Administrative Agent and the Lenders pursuant toSection 5.1.1.

"Available Borrowing Base" means, at the particular time in question, the Canadian Borrowing Base in effect minus the Canadian Effective
Amount at such time.

"Bankruptcy and Insolvency Act (Canada)" means theBankruptcy and Insolvency Act, S.C.
1992, c. 27, including the regulations made and, from time to time, in force, under that Act.

"Basin" means Basin Pipeline L.L.C., a Michigan limited liability company.

"BofA Canada" is defined in thepreamble.

"Borrower" is defined in thepreamble.

"Borrowing" means the Loans of the same type and, in the case of LIBO Rate Loans, having the same Interest Period made by all Lenders on
the same Business Day and pursuant to the same Borrowing Request in accordance withSection 2.1.

"Borrowing Request" means a loan request and certificate duly executed by an Authorized Officer of the Borrower, substantially in the form
ofExhibit Bhereto.

"Business Day" means (a) any day which is neither a Saturday or Sunday nor a legal holiday on which banks are authorized or
required to be closed in Dallas, Texas, Denver, Colorado, Toronto, Ontario, or Calgary, Alberta; and (b) relative to the making, continuing, prepaying or repaying of any LIBO Rate Loans, any
day on which dealings in Dollars are carried on in the interbank eurodollar market.

"Canadian Administrative Agent" is defined in thepreambleand includes each other Person
as shall have subsequently been appointed as the successor Canadian Administrative Agent pursuant toSection 9.4.

"Canadian Borrowing Base" means, if the U.S. Credit Agreement is effective, the Canadian Dollar Equivalent of the amount of the Global
Semi-Annual Borrowing Base allocated to the credit facilities hereunder pursuant toSections 2.1.3(a)(i) and 2.1.3(b)(i), or, if the
U.S. Credit Agreement is not effective, the amount determined pursuant toSections 2.1.3(a)(ii) and 2.1.3(b)(ii), provided,however, in no event shall the Canadian Borrowing Base ever exceed the Revolving Loan
Commitment Amount.

"Canadian Commitment Portion" means at any time during the Revolving Loan Availability Period, the Revolving Loan Commitment Amount in
effect at such time.

"Canadian Cost of Funds Rate" means a rate per annum equal to the cost of funds of the Canadian Administrative Agent as established by the
Canadian Administrative Agent based on its customary practice.

"Canadian Dollar Equivalent" with respect to an amount denominated in U.S. Dollars (a) means, for all purposes other than the
definition of "Canadian Borrowing Base' andSection 2.1.3, the amount

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of the Cdn. Dollars which would be required to purchase the relevant stated amount of U.S. Dollars based on an exchange rate equal to 1.5657, and (b) means, for purposes of a Global
Semi-Annual Borrowing Base determination pursuant toSection 2.1.3(a)of the U.S. Credit Agreement, and for the purposes of the
definition of "Canadian Borrowing Base,' the amount of Cdn. Dollars which would be required to purchase the relevant stated amount of U.S. Dollars based on the Noon Rate in effect on the effective
date of the applicable Reserve Report.

"Canadian Effective Amount" means, on any date, the aggregate outstanding principal amount of all Loans after giving effect to any
prepayments or repayments of Loans occurring on such dateplusthe Letter of Credit Outstandings.

"Canadian Prime Rate" means on any day a fluctuating rate of interest per annum equal to the rate of interest per annum most recently
announced by the Canadian Administrative Agent as its reference rate for Canadian Dollar commercial loans made to a Person in Canada. The Canadian Prime Rate plusthe Applicable Margin charged by any
Person shall never exceed the Highest Lawful Rate.

"Canadian Prime Rate Loan" means a Loan that bears interest at the Canadian Prime Rate plusthe Applicable Margin.

"Canadian Ratio" means at any time, an amount equal to (a) the Canadian Commitment Portion in effect at such time divided by(b) an amount equal to the sum of
(i) the U.S. Commitment Portion in effect at such time plus(ii) the Canadian Commitment Portion in effect at such time.

"Canadian Resident Lender" means each Lender identified as such on the signature pages to this Agreement or any Lender Assignment
Agreement executed by a new Lender, each being a Person whose Canadian business income is not treated as income of a non-resident of Canada for the purposes of the Income Tax Act(Canada).

"Capitalized Lease Liabilities" of a Person means all monetary obligations of such Person or any of its Subsidiaries under any leasing or
similar arrangement which, in accordance with GAAP, would be classified as capitalized leases, and, for purposes of this Agreement and each other Loan Document, the amount of such obligations shall be
the capitalized amount thereof, determined in accordance with GAAP, and the stated maturity thereof shall be the date of the last payment of rent or any other amount due under such lease prior to the
first date upon which such lease may be terminated by the lessee without payment of a penalty.

"Cash Collateralize" means to pledge and deposit with or deliver to the Canadian Administrative Agent, for the benefit of the Issuer and
the Lenders, as collateral for the Obligations in respect of Letters of Credit, cash or deposit account balances pursuant to documentation in form and substance satisfactory to the Canadian
Administrative Agent and the Issuer (which documents are hereby consented to by the Lenders). Derivatives of such term shall have corresponding meaning. The Borrower hereby grants the Canadian
Administrative Agent, for the benefit of the Issuer and the Lenders, a Lien on all such cash and deposit account balances. Cash collateral shall be maintained in blocked, non-interest
bearing deposit accounts at Canadian Administrative Agent or other institutions satisfactory to it.

"Cash Equivalent Investment" means, at any time: (a) any evidence of Indebtedness, maturing not more than one year after such time,
issued or guaranteed by the governments of the United States or Canada; (b) commercial paper, maturing not more than nine months from the date of issue, which is issued by (i) a
corporation (other than an Affiliate of any Obligor) organized under the laws of any state of the United States or of the District of Columbia, or under the laws of any province of Canada, and rated
A-l by Standard & Poor's Corporation or P-l by Moody's Investors Service, Inc., or (ii) any Lender (or its holding company); (c) any certificate of
deposit or bankers acceptance, maturing not more than one year after such time, which is issued by either (i) a commercial banking institution that

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is a member of the U.S. Federal Reserve System or is organized under the laws of Canada, or any province thereof, and in each case has a combined capital and surplus and undivided profits of not less
than the Canadian Dollar Equivalent of U.S. $250,000,000, or (ii) any Lender or an Affiliate thereof; (d) any repurchase agreement entered into with any Lender or an Affiliate thereof
(or other commercial banking institution of the stature referred to inclause (c)(i)) which (i) is secured by a fully perfected security
interest in any obligation of the type described in any ofclauses (a)through(c)); and (ii) has
a market value at the time such repurchase agreement is entered into of not less than 100% of the repurchase obligation of such Lender or Affiliate (or other commercial banking institution)
thereunder; (e) obligations of any state within the United States of America or any province of Canada, any nonprofit corporation or any instrumentality of the foregoing, provided,thatat the time of their purchase, such obligations are rated in one of the two highest
letter rating categories (e.g. in the case of Standard & Poor's Corporation, either its AAA or AA category) by a nationally recognized securities credit rating agency; (f) obligations
issued by political subdivisions or municipalities of any state within the United States of America or province within Canada, any nonprofit corporation or any instrumentality of the foregoing, provided,thatat the time of their purchase, such obligations are rated in one of the two highest
letter rating categories (e.g., in the case of Standard & Poor's Corporation, either its AAA or AA category) by a nationally recognized securities credit rating agency; or (g) eurodollar
deposits with the overseas branch of (i) any commercial banking institution that is a member of the Federal Reserve System or is organized under the laws of Canada, or any province thereof, and
in each case has a combined capital and surplus and undivided profits of not less than the Canadian Dollar Equivalent of U.S. $250,000,000, or (ii) any Lender or an Affiliate thereof.

"Change in Control (Parent)" means (a) the acquisition by any Person, or two or more Persons acting in concert (other than John Fox
and members of his family), of beneficial ownership (within the meaning of Rule 13d-3 of the Securities and Exchange Commission under the Securities Exchange Act of 1934) of 30% or
more of the outstanding shares of voting stock of the Parent; or (b) the failure of John Fox and members of his family to own, free and clear of all Liens or other encumbrances, at least 25% of
the outstanding shares of voting stock of the Parent on a fully diluted basis.

"Change in Control (Canadian Borrower)" means the failure of Parent to directly or indirectly own all of the stock or other equity
interests in the Borrower.

"Collateral" means all of the items and types of property described in now existing or hereafter created Collateral Documents and cash and
non-cash proceeds thereof.

"Collateral Documents" means each guaranty, pledge agreement, security agreement, mortgage, assignment, and all other security agreements,
deeds of trust, mortgages, chattel mortgages, assignments, pledges, guaranties, financing statements, continuation statements, extension agreements and other agreements or instruments previously
delivered or now or hereafter delivered by Borrower, Parent or any of the Subsidiaries of the Borrower or the MarkWest Inc. Subsidiaries to the Canadian Administrative Agent or the
Administrative Agent on behalf of the Lenders or to the Lenders in connection with this Agreement or any transaction contemplated hereby to secure or guarantee the payment of any part of the
Obligations or the performance of any other duties and obligations of Borrower under the Loan Documents, whenever made or delivered.

"Commitment Fee" means, on any date, a per annum fee equal to the commitment fee indicated in the pricing grid set forth in the definition
of Applicable Margin on such date.

"Commitment Termination Event" means (a) the occurrence of any Default described inclauses
(a)through(d)ofSection 8.1.9; or (b) the occurrence and
continuance of any other Event of Default and either (i) the declaration of the Loans and other Obligations to be due and payable pursuant to Section 8.3, or (ii) in the absence of such
declaration, the giving of notice by the Canadian Administrative Agent, acting at the
direction of the Required Lenders, to the Borrower that the Revolving Loan Commitments have been terminated.

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"Companies' Creditors Arrangement Act (Canada)" means theCompanies' Creditors Arrangement
Act, R.S.C. 1985, c. C-36, including the regulations made and from time to time in force under that Act.

"Consolidated Net Income" of the Parent means, for any period, the aggregate net income (or net loss, as the case may be) of the Parent
and its Subsidiaries for such period on a consolidated basis, determined in accordance with GAAP;provided, thatthere shall be excluded therefrom, without
duplication, (a) items classified as extraordinary (other than the tax benefit of the utilization
of net operating loss carry-forwards and alternative minimum tax credits); (b) any gain or loss, net of taxes, on the sale or other disposition of assets (including the capital stock or other
equity ownership of any other person, but excluding the sale of oil and gas inventories in the ordinary course of business); (c) any gain or loss, net of taxes, realized on the termination of
any employee pension benefit plan; (d) any adjustments of a deferred tax liability or asset pursuant to Statement of Financial Accounting Standards No. 109 which result from changes in
enacted tax laws or rates; (e) the cumulative effect of a change in accounting principles; and (f) impairment losses on oil and gas properties.

"Contingent Liability" means any agreement, undertaking or arrangement by which any Person guarantees, endorses or otherwise becomes or is
contingently liable upon (by direct or indirect agreement, contingent or otherwise, to provide funds for payment, to supply funds to, or otherwise to invest in, a debtor, or otherwise to assure a
creditor against loss) the indebtedness, obligation or any other liability of any other Person (other than by endorsements of instruments for deposit and/or in the
course of collection), or guarantees the payment of dividends or other distributions upon the shares of any other Person;provided, however, that
notwithstanding the foregoing, the definition of "Contingent Liability" shall not include (a) the Guaranty by each of the Parent
and the General Partner of the MLP dated March 26, 2002, given to Equitable Production Company in respect of Gas Processing Agreement (Maytown), the Pipeline Lease Agreement and the Equipment
Lease Agreement, each with Equitable Production Company and each dated as of May 28, 1999, and (b) any contingent payments owing by Parent or any of its Subsidiaries in connection with Section 2of the West Shore/Basin Purchase Agreement. The amount of any Person's obligation under any Contingent Liability shall (subject to any
limitation set forth therein) be deemed to be the outstanding principal amount (or maximum principal amount, if larger) of the debt, obligation or other liability guaranteed thereby.

"Continuation/Conversion Notice" means a notice of continuation or conversion and certificate duly executed by an Authorized Officer of
the Borrower, substantially in the form ofExhibit Chereto.

"Current Ratio" means the Current Ratio as defined in the U.S. Credit Agreement.

"Default" means any Event of Default or any condition, occurrence or event which, after notice or lapse of time or both, would constitute
an Event of Default.

"Default Rate" means the rate of interest set forth inSection 3.2.2.

"Disclosure Schedule" means the Disclosure Schedule attached hereto as Schedule 1.1(a), as it may be amended, supplemented or otherwise modified from time to time
by the Borrower with the written consent of the
Canadian Administrative Agent and the Required Lenders.

"Dollar" and "Cdn. Dollar" and the sign "Cdn. $" and "$" mean lawful money of Canada.

"Domestic" means, with respect to an entity, that such entity is incorporated, organized or formed under the laws of Canada, or any
province thereof.

"Domestic Office" means, relative to any Lender, the office of such Lender designated as such on in the Administrative Questionnaire
delivered to the Canadian Administrative Agent or designated in the Lender Assignment Agreement or such other office of a Lender (or any successor or assign of such Lender) within Canada as may be
designated from time to time by notice from such Lender, as the case may be, to each other Person party hereto.

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"EBITDA" means net earnings (excluding extraordinary items, gains and losses on sales and retirement of assets, non-cash write
downs and charges resulting from accounting convention changes) before deduction for federal and state income taxes, Interest Expense, net earnings attributable to minority interests, depreciation,
depletion and amortization expense and other non-cash charges and expenses, including, without limitation, non-cash charges and expenses relating to Hedging Agreements, of the
Parent and its Subsidiaries on a consolidated basis, all determined in accordance with GAAP. For purposes of calculating the Fixed Charge Coverage Ratio and the Leverage Ratio, EBITDA shall be
adjusted on a pro forma basis for any assets sold or acquired after the beginning of any four-Fiscal Quarter period being measured with respect to such ratios as if such assets had been
sold or acquired at the beginning of such four-Fiscal Quarter period,provided,however,
that (i) if during any consecutive twelve (12) month period the Purchase Price for Acquisitions by the Parent and its Subsidiaries equals or exceeds $5,000,000 in the aggregate, then pro
forma EBITDA attributable to Acquisitions in excess of $5,000,000 shall be taken into account only if and to the extent permitted by the Required Lenders and (ii) if during any consecutive
twelve (12) month period the sales price for assets sold by the Parent and its Subsidiaries equals or exceeds $5,000,000 in the aggregate, then pro forma EBITDA attributable to sales in excess
of $5,000,000 shall be taken into account only if and to the extent permitted by the Required Lenders.

"Effective Date" means the first date all conditions precedent inSection 5.1are
satisfied or waived in accordance withSection 10.1.

"Eligible Assignee" means (a) a Lender; (b) an Affiliate of a Lender; (c) an Approved Fund; and (d) any other
Person (other than a natural person) approved by (i) the Administrative Agent, (ii) in the case of any assignment of a Revolving Loan Commitment, the Letter of Credit issuing lender, and
(iii) unless an Event of Default has occurred and is continuing, the Borrower (each such approval not to be unreasonably withheld or delayed); providedthat notwithstanding the foregoing, "Eligible
Assignee" shall not include the Borrower or any of the Borrower's Affiliates or Subsidiaries.

"Environmental Laws" means all applicable federal, provincial, municipal, state or local statutes, laws, common law duties, ordinances,
codes, rules, regulations and guidelines (including consent decrees, administrative orders, directed duties, licenses and permits) relating to environmental, health, safety and land use matters.

"Event of Default" is defined inSection 8.1.

"Excluded MLP Entities" means the MLP, MarkWest OLLC, and their Subsidiaries.

"Existing Collateral Documents" has the meaning set forth inSection 10.23.

"Existing Credit Agreement" is defined in the second recital.

"Existing Lenders" is defined in the second recital.

"Existing Loans" is defined in the second recital.

"Existing Mortgages" means the deeds of trust and mortgages listed on Schedule 10.23hereto.

"Federal Funds Rate" means, for any day, a fluctuating interest rate per annum (rounded upwards to the nearest 1/100 of 1%) equal to
(a) the weighted average of the rates on overnight federal funds transactions with members of the U.S. Federal Reserve System arranged by federal funds brokers, as published for such day (or,
if such day is not a Business Day, for the next preceding Business Day as so published on the next succeeding Business Day) by the Federal Reserve Bank of New York; or (b) if such rate is not
so published on the next succeeding Business Day, the Federal Funds Rate for such day shall be the average rate charged to the Canadian Administrative Agent on such day on such transactions as
determined by the Canadian Administrative Agent.

"Fiscal Quarter" means any quarter of a Fiscal Year.

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"Fiscal Year" means any period of twelve consecutive calendar months ending on December 31; references to a Fiscal Year with a
number corresponding to any calendar year (e.g., the "2000 Fiscal Year") refer to the Fiscal Year ending on December 31 during such calendar
year.

"Fixed Charges" for any period ending on a calculation date means the sum of (a) Interest Expense for such period, plus(b) dividends paid, declared or
required to be paid in such period in respect of common and preferred stock.

"Fixed Charge Coverage Ratio" as of a date means the ratio of (a) EBITDA for the four Fiscal Quarters ended on such date to
(b) Fixed Charges for such four-Fiscal Quarter period.

"F.R.S. Board" means the Board of Governors of the Federal Reserve System or any successor thereto.

"Fund" means any Person (other than a natural person) that is (or will be) engaged in making, purchasing, holding or otherwise investing
in commercial loans and similar extensions of credit in the ordinary course of its business.

"GAAP" is defined inSection 1.4.

"Global Lenders" has the meaning set forth in the U.S. Credit Agreement.

"Global Semi-Annual Borrowing Base" means, at the particular time in question, the amount provided for in Section 2.1.3,provided,however, in no event
shall the Global Semi-Annual Borrowing Base ever exceed the sum of (i) the U.S. Dollar Equivalent of the Revolving Loan Commitment Amount and (ii) the Revolving Loan
Commitment Amount as defined in and outstanding under the U.S. Credit Agreement.

"Guaranty" means any guaranty agreement executed and delivered pursuant to Section 5.1.3orSection 7.1.8,
substantially in the form of Exhibit G-1orG-2hereto, as amended, supplemented, restated or
otherwise modified from time to time.

"Hazardous Materials" means all those substances that are regulated by, or which may form the basis of liability under, any Environmental
Law, including any substance identified under any Environmental Law as a pollutant, contaminant, hazardous waste, hazardous constituent, special waste, hazardous substance, hazardous material, or
toxic substance, or petroleum or petroleum derived substance or waste.

"Hedging Agreement" for a Person means any interest rate swap agreements, interest rate cap agreements, interest rate collar agreements,
commodity price protection agreements, foreign exchange protection agreements, and all other agreements or arrangements designed to protect such Person against fluctuations in interest rates,
commodity prices, or foreign exchange rates, as any such agreement is amendment, supplemented or otherwise modified from time to time.

"Hedging Counterparty" means any Person which is a counterparty to a Hedging Agreement.

"Hedging Obligation" means, with respect to any Person, all liabilities of such Person under any Hedging Agreement.

"Hedging Policy" means the Borrower's Risk Management Policies and Procedures dated September 2001, as amended in accordance with Section 7.2.1.

"herein," "hereof," "hereto,"
"hereunder" and similar terms contained in this Agreement or any other Loan Document refer to this Agreement or such other Loan Document, as the case
may be, as a whole and not to any particular Section, paragraph or provision of this Agreement or such other Loan Document.

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"Highest Lawful Rate" means, with respect to each Lender to whom Obligations are owed, the maximum nonusurious rate of interest that such
Lender is permitted under applicable law to contract for, take, charge, or receive with respect to such Obligations. All determinations herein of the Highest Lawful Rate, or of any interest rate
determined by reference to the Highest Lawful Rate, shall be made separately for each Lender as appropriate to assure that the Loan Documents are not construed to obligate any Person to pay interest
to any Lender at a rate in excess of the Highest Lawful Rate applicable to such Lender.

"Hydrocarbon Interests" means leasehold and other interests in or under oil, gas and other liquid or gaseous hydrocarbon leases with
respect to Oil and Gas Properties wherever located, mineral fee interests, overriding royalty and royalty interests, net profit interests, production payment interests relating to oil, gas or other
liquid or gaseous hydrocarbons wherever located including any reserved or residual interest of whatever nature.

"include" and "including" mean including without limiting the generality of any
description preceding each such term, and, for purposes of this Agreement and each other Loan Document, the parties hereto agree that a general statement, which is followed by or referable to an
enumeration of specific matters, shall not be limited to matters similar to the matters specifically mentioned.

"Income Tax Act (Canada)" means theIncome Tax Act, S.C.
1970-71-72, c. 63, including the regulations made and, from time to time, in force under that Act.

"Indebtedness" of any Person means, without duplication: (a) all obligations of such Person for borrowed money and all obligations
of such Person evidenced by bonds, debentures, notes or other similar instruments; (b) all obligations, contingent or otherwise, relative to the face amount of all letters of credit, whether or
not drawn, and banker's acceptances issued for the account of such Person; (c) all obligations of such Person as lessee under leases which have been or should be, in accordance with GAAP,
recorded as Capitalized Lease Liabilities; (d) all other items which, in accordance with GAAP,
would be included as liabilities on the liability side of the balance sheet of such Person as of the date at which Indebtedness is to be determined other than non-cash items, such as
deferred taxes, required by GAAP to be included as liabilities on the balance sheet; (e) net liabilities of such Person under all Hedging Obligations except for non-cash
mark-to-market adjustments required by GAAP; (f) all obligations of such Person to pay the deferred purchase price of property or services (whether or not required to be
included as liabilities in accordance with GAAP) and indebtedness (excluding prepaid interest thereon) secured by a Lien on property owned or being purchased by such Person (including indebtedness
arising under conditional sales or other title retention agreements), whether or not such indebtedness shall have been assumed by such Person; and (g) all Contingent Liabilities of such Person
in respect of any of the foregoing;provided,however, that for the purposes of this definition, a
production payment or similar transaction which is non-recourse to such Person and payments owing by Parent or any of its Subsidiaries in connection with the West Shore/Basin Purchase
Agreement shall not constitute "Indebtedness." For all purposes of this Agreement, the Indebtedness of any Person shall include the Indebtedness of any partnership or joint venture in which such
Person is a general partner or a joint venturer unless such Indebtedness is expressly non-recourse to such general partner or joint venturer.

"Indemnified Liabilities" is defined inSection 10.4.

"Indemnified Parties" is defined inSection 10.4.

"Independent Engineer" has the meaning set forth inSection 7.1.1(k).

"Insurance Deposit Account" is defined inSection 7.1.5.

"Intercreditor Agreement" means that certain Amended and Restated Intercreditor Agreement dated as of even date herewith, by and among the
Canadian Administrative Agent, the Lenders

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hereunder, the Administrative Agent, and the lenders under the U.S. Credit Agreement, substantially in the form ofExhibit Jattached hereto, as
amended, supplemented, restated or otherwise modified from time to time.

"Interest Act (Canada)" means theInterest Act, R.S.C. 1985, c. I-15,
including the regulations made and, from time to time, in force under that Act.

"Interest Expense" means, for any period, for the Parent and its Subsidiaries on a consolidated basis, the sum of (a) all interest,
premium payments, fees, charges and related expenses of the Parent and its Subsidiaries in connection with borrowed money (including capitalized interest and including fees
payable in respect of letters of credit and bankers' acceptances) or in connection with the deferred purchase price of assets, in each case to the extent treated as interest in accordance with GAAP,
and (b) the portion of rent expense of the Parent and its Subsidiaries with respect to such period under capital leases that is treated as interest in accordance with GAAP; provided,however, that the issuance of PIK Notes shall not be included in the calculation of Interest
Expense. For purposes of calculating the Fixed Charge Coverage Ratio, if, in connection with an Acquisition, any Indebtedness is incurred or assumed by the Parent or any of its Subsidiaries, then
Interest Expense shall be adjusted on a pro forma basis (in a manner acceptable to the Required Lenders) for the four-Fiscal Quarter period most recently completed, as if such Indebtedness
had been incurred or assumed at the beginning of such four-Fiscal Quarter period.

"Interest Period" means, relative to any LIBO Rate Loans, the period beginning on (and including) the date on which such LIBO Rate Loan is
made or continued as, or converted into, a LIBO Rate Loan pursuant toSection 2.3or2.4and
shall end on (but exclude) the day which numerically corresponds to such date one, two, three or six months thereafter (or, if such month has no numerically corresponding day, on the last Business Day
of such month), in either case as the Borrower may select in its relevant notice pursuant toSection 2.3or 2.4;provided,however, that (a) the Borrower
shall not be permitted to select Interest Periods to be in effect at any one time which have expiration dates occurring on more than four different dates; (b) Interest Periods commencing on the
same date for Loans comprising part of the same Borrowing shall be of the same duration; (c) if such Interest Period would otherwise end on a day which is not a Business Day, such Interest
Period shall end on the next following Business Day (unless, if such Interest Period applies to LIBO Rate Loans, such next following Business Day is the first Business Day of a calendar month, in
which case such Interest Period shall end on the Business Day next preceding such numerically corresponding day); and (d) no Interest Period may end later than the Stated Maturity Date.

"Investment" means, relative to any Person, (a) any loan or advance made by such Person to any other Person (excluding travel and
similar advances not to exceed Cdn. $313,140 in the aggregate for all such advances to officers and employees made in the ordinary course of business, and relocation advances made to officers and
employees in the ordinary course of business); (b) any Contingent Liability of such Person; and (c) any ownership or similar interest held by such Person in any other Person. The amount
of any Investment shall be the original principal or capital amount thereof less all returns of principal or equity thereon (and without adjustment by reason of the financial condition of such other
Person) and shall, if made by the transfer or exchange of property other than cash, be deemed to have been made in an original principal or capital amount equal to the fair market value of such
property.

"Issuance Request" means a request and certificate duly executed by the chief executive, accounting or financial Authorized Officer of the
Borrower, substantially in the form ofExhibit Iattached hereto (with such changes thereto as may be agreed upon from time to time by the
Canadian Administrative Agent, the Issuer and the Borrower).

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"Issuer" means the Canadian Administrative Agent or any other Lender which has agreed to issue one or more Letters of Credit at the
request of the Canadian Administrative Agent (which shall, at the Borrower's request, notify the Borrower from time to time of the identity of such other Lender).

"Judgment Interest Act (Alberta)" means theJudgment Interest Act, S.A. 1984 c.
J-O.5, including the regulations made and, from time to time, in force under that Act.

"Lender Assignment Agreement" means a Lender Assignment Agreement, substantially in the form of Exhibit Dhereto.

"Lender Hedging Agreement" means any Hedging Agreements entered into by Borrower or any of the MarkWest Inc. Operating Subsidiaries
in which a Lender or an Affiliate of a Lender is the Hedging Counterparty.

"Lenders" is defined in the preamble.

"Letter of Credit" is defined inSection 2.6.

"Letter of Credit Commitment" means, relative to any Lender, such Lender's obligation to issue (in the case of an Issuer) or participate
in (in the case of all Lenders) Letters of Credit pursuant toSection 2.1.2.

"Letter of Credit Outstandings" means, at any time, an amount equal to the sum of (a) the aggregate Stated Amount at such time of
all Letters of Credit then outstanding and undrawn (as such aggregate Stated Amount shall be adjusted, from time to time, as a result of drawings, the issuance of Letters of Credit, or otherwise), plus(b) the then aggregate amount of all unpaid and outstanding Reimbursement Obligations.

"Letter of Credit Sublimit" means the amount of Cdn. $7,828,500.

"Leverage Ratio" means, as of a date, the ratio of (a) Total Funded Debt to (b) EBITDA for the four Fiscal Quarters most
recently ended prior to such date.

"LIBO Rate" means, relative to any Interest Period for LIBO Rate Loans, (a) the interest rate per annum (carried out to the fifth
decimal place) equal to the rate determined by the Canadian Administrative Agent to be the offered rate that appears on the page of the Telerate Screen that displays an average British Bankers
Association Interest Settlement Rate (such page currently being page number 3740) for deposits in Cdn. Dollars (for delivery on the first day of such Interest Period) with a term equivalent to such
Interest Period, determined as of approximately 11:00 a.m. (London time) two Business Days prior to the first day of such Interest Period, or (b) in the event the rate referenced in the
precedingsubsection (a)does not appear on such page or service or such page or service shall cease to be available, the rate per annum (carried out to
the fifth decimal place) equal to the rate determined by the Canadian Administrative Agent to be the offered rate on such other page or other service that displays an average British Bankers
Association Interest Settlement Rate for deposits in Cdn. Dollars (for delivery on the first day of such Interest Period) with a term equivalent to such Interest Period, determined as of approximately
11:00 a.m. (London time) two Business Days prior to the first day of such Interest Period, or (c) in the event the rates referenced in the precedingsubsections
(a)and(b)are not available, the rate per annum determined by the Canadian Administrative Agent as the rate of interest at
which deposits in Cdn. Dollars (for delivery on the first day of such Interest Period) in same day funds in the approximate amount of the applicable LIBO Rate Loan and with a term equivalent to such
Interest Period would be offered by its London branch to major banks in the offshore Cdn. Dollar market at their request at approximately 11:00 a.m. (London time) two Business Days prior to the
first day of such Interest Period.

"LIBO Rate Loan" means a Loan bearing interest, at all times during an Interest Period applicable to such Loan, at a fixed rate of
interest determined by reference to the LIBO Rate (Reserve Adjusted).

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"LIBO Rate (Reserve Adjusted)" means, relative to any Loan to be made, continued or maintained as, or converted into, a LIBO Rate Loan for
any Interest Period, a rate per annum (rounded upwards, if necessary, to the nearest 1/16 of 1%) determined pursuant to the following formula:

LIBO Rate
(Reserve Adjusted)

=

LIBO Rate1.00 - LIBOR Reserve Percentage


The
LIBO Rate (Reserve Adjusted) for any Interest Period for LIBO Rate Loans will be determined by the Canadian Administrative Agent on the basis of the LIBOR Reserve Percentage in
effect on, and the applicable LIBO Rates furnished to and received by the Canadian Administrative Agent from BofA Canada, two Business Days before the first day of such Interest Period.

"LIBOR Office" means, relative to any Lender, the office of such Lender designated as such in the Administrative Questionnaire delivered
to the Canadian Administrative Agent or designated in the Lender Assignment Agreement or such other office of a Lender as designated from time to time by notice from such Lender to the Borrower and
the Canadian Administrative Agent, whether or not outside Canada, which shall be making or maintaining LIBO Rate Loans of such Lender hereunder.

"LIBOR Reserve Percentage" means, relative to any Interest Period for LIBO Rate Loans, the reserve percentage (expressed as a decimal)
equal to the maximum aggregate reserve requirements (including all basic, emergency, supplemental, marginal and other reserves and taking into account any transitional adjustments or other scheduled
changes in reserve requirements) specified under regulations issued from time to time by the F.R.S. Board and then applicable to assets or liabilities consisting of and including "Eurocurrency
Liabilities," as currently defined in Regulation D of the F.R.S. Board, having a term approximately equal or comparable to such Interest Period. Without limiting the effect of the foregoing,
the Reserve Requirement shall reflect any other reserves required to be maintained under such regulations with respect to any category of liabilities which includes deposits by reference to which the
LIBO Rate (Reserve Adjusted) is to be determined.

"Lien" means any security interest, mortgage, pledge, hypothecation, assignment, deposit arrangement, encumbrance, lien (statutory or
otherwise), charge against or interest in property to secure payment of a debt or performance of an obligation or other priority or preferential arrangement of any kind or nature whatsoever.

"Loan" means an extension of credit by a Lender to the Borrower pursuant to Article II.

"Loan Documents" means this Agreement, the Notes, each of the Collateral Documents, each Guaranty, any Agreement Regarding Collateral, the
Intercreditor Agreement, and each other agreement, document or instrument delivered by the Borrower, the Parent or any of the Subsidiaries of
the Borrower or the MarkWest Inc. Subsidiaries from time to time in connection with this Agreement and the Notes each as amended, restated or otherwise modified from time to time. In addition,
references to "Loan Documents" in the Collateral Documents shall include Lender Hedging Agreements.

"Margin Stock" means margin stock as defined in Regulation U.

"MarkWest Inc. Operating Subsidiaries" means any Subsidiary of the Parent other than the MLP Parties.

"MarkWest Inc. Subsidiaries" means any Subsidiary of the Parent other than the Excluded MLP Entities.

"MarkWest Michigan" means MarkWest Michigan, Inc., a Colorado corporation.

"MarkWest OLLC" means MarkWest Energy Operating Company, L.L.C., a Delaware limited liability company and a wholly-owned Subsidiary of the
MLP.

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"MarkWest OLLC Credit Agreement" means that certain Credit Agreement dated as of even date herewith among MarkWest OLLC as borrower, Bank
of America, N.A. as administrative agent, and the financial institutions from time to time party thereto, and all refinancing and increases thereof.

"MarkWest Resources" means MarkWest Resources, Inc., a Colorado corporation.

"Material Adverse Effect" means with respect to any matter that such matter could reasonably be expected to materially and adversely
affect the assets, business, properties, financial condition or prospects, or results or operations of the Parent and the MarkWest Inc. Operating Subsidiaries taken as a whole, or the ability
of the Borrower or any other Obligor to perform in a material respect its respective obligations under any of the Loan Documents.

"Matrex" means Matrex, L.L.C., a Michigan limited liability company.

"Midstream Business" means any and all operations of the Borrower and its Domestic Subsidiaries in Canada related to the gathering and
processing of natural gas and the fractionation, transportation, marketing, and storage of natural gas liquids.

"Midstream Report" means a report, covering the Midstream Business, and any related non-Oil and Gas Properties businesses,
prepared in accordance with customary and prudent practices in form and substance acceptable to the Administrative Agent, setting forth (a) the total quantity of gas and liquids to be gathered,
processed and fractionated, (b) the estimated future net revenues and cumulative estimated future net revenues, (c) the present discounted value of future net revenues, and
(d) such other information and data with respect to the Midstream Business, and any related non-Oil and Gas Properties businesses, as the Administrative Agent may reasonably
request.

"Midstream Services" means MarkWest Canadian Midstream Services Inc., an Alberta corporation.

"MLP" means MarkWest Energy Partners, L.P., a Delaware limited partnership.

"MLP Credit Agreement Default" means a Default or Event of Default under the MarkWest OLLC Credit Agreement or the occurrence of any event
or condition the effect of which is to cause or to permit the holder of Indebtedness under the MarkWest OLLC Credit Agreement to cause such Indebtedness to be due.

"MLP Party" means the MLP, the MLP's General Partner and the MLP's Subsidiaries.

"MLP Transfer" means the conveyance of assets by the Borrower and certain of the MarkWest Inc. Subsidiaries to the MLP on the
Effective Date pursuant to the Contribution Agreement dated as of the Effective Date by and among the Parent, certain of its Subsidiaries, and the MLP.

"MLP's General Partner" means MarkWest Energy GP, L.L.C., a Delaware limited liability company, a subsidiary of the Parent, that is the
general partner of the MLP.

"Monthly Payment Date" means the last day of each calendar month or, if any such day is not a Business Day, the next succeeding Business
Day.

"Mortgages" means the Amended and Restated Fixed Charge Mortgage dated as of even date with this Agreement (substantially in the form of Exhibit H-3hereto)
executed by the Borrower in connection herewith as amended, restated, or otherwise modified from time to time,
and any and all other
mortgages that may be executed in the future securing all or any part of the Obligations, executed by the Borrower, any of its Subsidiaries or any other Person.

"Non-Recourse" means, with reference to obligations, (a) the MLP's General Partner shall not have any obligation or
liability with respect thereto, contingent, direct or otherwise, including, without limitation, any guaranty obligation, and any obligation (i) to purchase or pay such obligations,
(ii) to purchase or lease property, securities or services for the purpose of assuring the obligee in respect of Indebtedness or other obligation, or (iii) to maintain working capital,
equity capital or any other

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financial statement condition or liquidity, and (b) no assets of the MLP's General Partner shall be encumbered by a Lien securing any such Indebtedness or other Obligations.

"Non-resident Lender" means any Lender which is not a Canadian Resident Lender, and shall initially mean each Lender
identified as such on the signature pages to this Agreement or thereafter on any Lender Assignment Agreement.

"Noon Rate" means, in relation to the conversion of one currency into another currency, the rate of exchange for such conversion as quoted
by the Bank of Canada (or, if not so quoted, the spot rate of exchange quoted for wholesale transactions made by Canadian Administrative Agent at Toronto, Ontario at approximately noon (Toronto,
Ontario local time)).

"Note" means a promissory note of the Borrower payable to any Lender, in substantially the form of Exhibit Ahereto (as such promissory note may be amended,
endorsed or otherwise modified from time to time), evidencing the aggregate Obligations
of the Borrower to such Lender resulting from outstanding Loans and Reimbursement Obligations, and also means all other promissory notes accepted from time to time in substitution therefor or renewal
thereof.

"Obligations" means all obligations (monetary or otherwise) of the Borrower and each other Obligor arising under or in connection with
this Agreement, the Notes, the Reimbursement Obligations and each other Loan Document. In addition, all references to "Obligations" in the Collateral Documents and inSections
4.8,4.9and10.16shall, in addition to the foregoing, also include all present
and future indebtedness, liabilities and obligations (and all renewals and extensions thereof or any part thereof) now or hereafter owed by the Borrower and each other Obligor to any Lender or any
Affiliate of a Lender pursuant to a Lender Hedging Agreement.

"Obligor" means the Borrower, Parent or any other Person (other than the Canadian Administrative Agent or any Lender) obligated under any
Loan Document.

"Offer of Extension" means a written offer by Canadian Administrative Agent, for and on behalf of Required Lenders, to Borrower to extend
the Revolving Loan Availability Period to a date 364 days from acceptance by Borrower of such offer, and setting forth, if applicable, the terms and conditions on which such extension is
offered by the Lenders and as may be accepted by Borrower.

"Oil and Gas" means petroleum, natural gas and other related hydrocarbons or minerals or any of them and all other substances produced or
extracted in association therewith.

"Oil and Gas Properties" means Hydrocarbon Interests now owned or hereafter acquired by the Borrower and its Subsidiaries and contracts
executed in connection therewith and all tenements, hereditaments, appurtenances, and properties belonging, affixed or incidental to such Hydrocarbon Interests, including, without limitation, any and
all property, real or personal, now owned by the Borrower and its Subsidiaries and situated upon or to be situated upon, and used, built for use, or useful in connection with the operating, working or
developing of such Hydrocarbon Interests, including, without limitation, any and all petroleum and/or natural gas wells, buildings, structures, field separators, liquid extractors, plant compressors,
pumps, pumping units, field gathering systems, tank and tank batteries, fixtures, valves, fittings, machinery and parts, engines, boilers, liters, apparatus, equipment, appliances, tools, implements,
cables, wires, towers, taping, tubing and rods, surface leases, rights-of-way, easements and servitudes, and all additions, substitutions, replacements for, fixtures and
attachments to any and all of the foregoing owned directly or indirectly by the Borrower and its Subsidiaries.

"Organic Document" means, relative to any Obligor, its certificate of incorporation, articles of formation, operating agreement, its
by-laws and all shareholder agreements, voting trusts and similar arrangements applicable to any of its authorized shares of capital stock or equity interests.

"Parent" is defined in thefourth recital.

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"Parent Guaranty" means the Guaranty in substantially the form attached as Exhibit G-1hereto, executed by the Parent in connection herewith as amended, restated or
otherwise modified from time to time.

"Participant" has the meaning assigned to such term in clause (d) of Section 10.10.

"Percentage" means, relative to any Lender, the percentage set forth onSchedule 1.1(b)hereto or set forth in a Lender Assignment Agreement, as such percentage may be adjusted from time to time pursuant to Lender Assignment Agreement(s) executed by such Lender and its Eligible
Assignee(s) and
delivered pursuant toSection 10.10;provided, thatthe sum of all Percentages for all Lenders shall
never be less than 100%.

"Permitted Liens" has the meaning set forth inSection 7.2.3.

"Person" means any natural person, corporation, partnership, firm, association, trust, government, governmental agency or any other
entity, whether acting in an individual, fiduciary or other capacity.

"PIK Notes" means Subordinated Notes that may be issued pursuant to Subordinated Debt Documents in connection with the Parent's exercise
of its option to elect to pay accrued and unpaid interest on Subordinated Debt by delivery of additional Subordinated Notes.

"Purchase Price" means, with respect to any Acquisition, all direct, indirect, and deferred cash and non-cash payments made to
or for the benefit of the Person being acquired (or whose assets are being acquired), its shareholders, officers, directors, employees, or Affiliates in connection with such Acquisition, including,
without limitation, the amount of any Indebtedness being assumed in connection with such Acquisition and (subject to the limitations on Indebtedness hereunder) seller financing, payments under
non-competition or consulting agreements entered into in connection with such Acquisition and similar agreements, all non-cash consideration and the value of any stock,
options, or warrants or other rights to acquire stock issued as part of the consideration in such transactions.

"Quarterly Payment Date" means the last day of each March, June, September and December or, if any such day is not a Business Day, the
next succeeding Business Day.

"Quarterly Status Report" means a status report prepared quarterly by the Parent in form, scope and content acceptable to the Canadian
Administrative Agent (a) detailing production from the Oil and Gas Properties, the volumes of Oil and Gas produced and saved, the volumes of Oil and Gas sold, gross revenue, net income, related
leasehold operating expenses, severance taxes, other taxes, capital costs and any production imbalances incurred during such period, (b) describing the Parent's and the MarkWest Inc.
Operating Subsidiaries' respective position regarding its Hedging Agreements with respect to its Oil and Gas Properties including the amount contracted in volumes and as a percentage of such company's
total anticipated production, length of contracts, and the price or prices hedged, and (c) setting forth such additional information with respect to any of Parent's and the MarkWest Inc.
Operating Subsidiaries' Oil and Gas Properties as may be reasonably requested by Canadian Administrative Agent, in each case for such quarter then ended.

"Redeemable Preferred Stock" means preferred stock that has, or is convertible into any security that has, mandatory redemption or
repurchase requirements (other than those exercisable solely at the option of the issuer of said stock) on or prior to the date set forth in the definition of Stated Maturity Date.

"Regulation U" means Regulation U of the Board of Governors of the Federal Reserve System.

"Reimbursement Obligation" is defined inSection 2.6.5.

"Related Parties" means, with respect to the Administrative Agent, the Canadian Administrative Agent, and the Lenders, such Person's
Affiliates and the respective directors, officers, employees, agents and advisors of such Person and such Person's Affiliates.

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"Required Global Lenders" has the meaning set forth in the U.S. Credit Agreement.

"Required Lenders" means, at any time, the Canadian Administrative Agent and two or more Lenders holding at least 66% of the then
aggregate outstanding principal amount of the Notes then held by the Lenders, or, if no such principal amount is then outstanding, the Canadian Administrative Agent and Lenders having at least 66% of
the aggregate Revolving Loan Commitments.

"Reserve Report" means a report, prepared in accordance with guidelines and requirements of the United States Securities and Exchange
Commission in form acceptable to the Canadian Administrative Agent, covering proved developed and proved undeveloped Oil and Gas reserves attributable to Borrower's and its Subsidiaries' Oil and Gas
Properties and setting forth with respect thereto, (a) the total quantity of proved developed and proved undeveloped reserves (separately classified as to producing, shut-in, behind
pipe, and undeveloped), (b) the estimated future net revenues and cumulative estimated future net revenues, (c) the present discounted value of future net revenues, and (d) such
other information and data with respect to the Oil and Gas Properties as the Canadian Administrative Agent may reasonably request.

"Revolving Loan" means a loan made pursuant toSection 2.1.1.

"Revolving Loan Availability Period" has the meaning set forth inSection 2.1.1(c).

"Revolving Loan Commitment" means, relative to any Lender, such Lender's obligation to make Revolving Loans pursuant to Section 2.1.1.

"Revolving Loan Commitment Amount" means on any date, Cdn. $54,799,500 as such amount may be increased from time to time pursuant to Section 2.1.6and as may be
reduced from time to time pursuant toSection 2.2.

"Revolving Loan Commitment Termination Date" means the earliest of (a) the Stated Maturity Date, (b) the date on which the
Revolving Loan Commitment Amount is terminated in full or reduced to zero pursuant toSection 2.2, and (c) the date on which any
Commitment Termination Event occurs. Upon the occurrence of any event described inclause (b)or (c), the Revolving Loan Commitments shall terminate
automatically and without any further action.

"rights" means rights, remedies, powers, privileges and benefits.

"Schedule I BA Reference Banks" means the Lenders listed inSchedule Ito
theBank Act(Canada) as are, at such time, designated by the Canadian Administrative Agent, with the prior consent of the Borrower (acting reasonably),
as the Schedule I BA Reference Banks.

"Schedule II BA Reference Banks" means the Lenders listed inSchedule IIto
theBank Act(Canada) as are, at such time, designated by the Canadian Administrative Agent, with the prior consent of the Borrower (acting reasonably),
as the Schedule II BA Reference Banks.

"Security Agreements" means the General Security Agreement, the Security Pledge Agreement, and the Mortgage, each substantially in the
form ofExhibits H-1,H-2.

"Semi-Annual Borrowing Base Period" means the period from March 29, 2002, to August 31, 2002, and each
six-month period commencing September 1, 2002, and each subsequent March 1 and September 1 thereafter.

"Special Canadian Borrowing Base Determination" is defined inSection 2.1.3(b)(ii).

"Stated Amount" of each Letter of Credit means the face amount of such Letter of Credit as such amount is in effect on the issuance date
thereof.

"Stated Expiry Date" is defined inSection 2.6.1.

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"Stated Maturity Date" means in the case of any unpaid and outstanding Reimbursement Obligations, or any Letter of Credit, or any Loan,
August 9, 2004.

"Subordinated Debt" means Indebtedness of the Parent that the Parent designates as "Subordinated Indebtedness" hereunder by giving written
notice to the Canadian Administrative Agent, which Indebtedness is issued upon, and that is governed by documents containing, terms and conditions satisfactory to the Required Lenders in their sole
discretion and that is subordinated to the Obligations upon terms and conditions satisfactory to the Required Lenders in their sole discretion.

"Subordinated Debt Documents" means documents executed in connection with Subordinated Debt.

"Subordinated Notes" means promissory notes evidencing Subordinated Debt.

"Subordination Agreement" means a subordination agreement or other agreement containing the terms upon which Subordinated Debt is
subordinated to the "Obligations" under the U.S. Credit Agreement.

"Subsidiary" of a Person means a corporation, partnership, joint venture, limited liability company or other business entity of which a
majority of the shares of securities or other interests having ordinary voting power for the election of directors or other governing body (other than securities or interests having such power only by
reason of the happening of a contingency) are at the time beneficially owned, or the management of which is otherwise controlled, directly, or indirectly through one or more intermediaries, or both,
by such Person. Unless otherwise specified, all references herein to a "Subsidiary" or to "Subsidiaries" shall refer to a Subsidiary or Subsidiaries of the Borrower.

"Tangible Net Worth" means the consolidated net worth of the Parent and its Subsidiaries (excluding any Redeemable Preferred Stock) after
subtracting therefrom the aggregate amount of any Intangible Assets of the Parent and its Subsidiaries. "Intangible Assets" means the amount (to the
extent reflected in determining consolidated net worth) of all unamortized debt discount and expense (to the extent, if any, recorded as an unamortized deferred charge), unamortized deferred charges,
goodwill, franchises, licenses, patents, trademarks, trade names, copyrights, service marks and brand names;provided, thatfor purposes of this definition,
 consolidated net worth shall be adjusted to exclude non-cash items, including foreign currency
translation adjustments, unrealized gains and losses, and mark-to-market adjustments relating to Hedging Agreements, pursuant to GAAP.

"Taxes" is defined inSection 4.6.

"Total Funded Debt" means, as of any date, the sum without duplication of (a) the outstanding principal amount of all Indebtedness
of the Parent and its Subsidiaries of the nature referred to inclauses (a),(b), (c)and(f)of the definition of Indebtedness and (b) all Redeemable Preferred Stock of the
Parent and its Subsidiaries, valued at the redemption price thereof;provided,however, in the event
that Parent's "working capital" (determined in accordance with GAAP, but excluding non-cash mark-to-market adjustments relating to Hedging Agreements required to be
made under GAAP) is greater than $0 at any time at which the Parent's Total Funded Debt is calculated, then Total Funded Debt for such time period shall equal the outstanding principal amount of all
Indebtedness of the Parent and its Subsidiaries of the nature referred to inclauses (a),(b), (c)and(f)of the definition of Indebtednessplusall
Redeemable Preferred Stock of the Parent and its Subsidiaries,lesscash on hand or Cash Equivalent Investments which are free and clear of all Liens,
other than Liens securing the Loans and "Liens" securing the "Loans" under the U.S. Credit Agreement.

"type" means, relative to any Loan, the portion thereof, if any, being maintained as a Canadian Prime Rate Loan or a LIBO Rate Loan.

"U.S. Borrowing Base" means the sum of (i) the Global Semi-Annual Borrowing Base allocated to the credit facilities
governed by the U.S. Credit Agreement pursuant toSection 2.1.3thereof and (ii) the U.S. Monthly Borrowing Base (as defined in the U.S.
Credit Agreement),provided,however, in

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no event shall the U.S. Borrowing Base ever exceed the Revolving Loan Commitment Amount outstanding under the U.S. Credit Agreement.

"U.S. Commitment Portion" at any time means an amount equal to the Canadian Dollar Equivalent of the Revolving Loan Commitment Amount as
defined in the U.S. Credit Agreement in effect at such time then outstanding.

"U.S. Credit Agreement" means that certain Fifth Amended and Restated Credit Agreement dated of even date herewith, among Parent, the
lenders from time to time party thereto, and Bank of America, N.A., as administrative agent, as amended and as in effect from time to time.

"U.S. Dollar" or "U.S. $" means the lawful currency of the United States of America.

"U.S. Dollar Equivalent" with respect to an amount denominated in Cdn. Dollars (a) means, for purposes of the definition of Global
Borrowing Base and for purposes of a Global Semi-Annual
Borrowing Base determination pursuant toSection 2.1.3(a)of the U.S. Credit Agreement, the amount of U.S. Dollars required to purchase the
relevant stated amount of Cdn. Dollars based on the Noon Rate in effect on the effective date of the relevant Reserve Report and (b) means, for all purposes other than those described in the
foregoing clause (a), the amount of U.S. Dollars required to purchase the relevant stated amount of Cdn. Dollars based on the Noon Rate in effect on the day of determination.

"U.S. Effective Amount" means, on any date, the aggregate outstanding principal amount of all Loans under the U.S. Credit Agreement after
giving effect to any prepayments or repayments of such Loans occurring on such dateplusthe Letter of Credit Outstandings under the U.S. Credit
Agreement.

"U.S. Parent Pledge and Security Agreement" means the Second Amended and Restated Security Agreement dated as of October 12, 2001,
executed by the Parent.

"U.S. Subsidiary Pledge and Security Agreement" means each Pledge and Security Agreement now or hereafter executed by a Subsidiary of the
Parent.

"United States" or "U.S." means the United States of America, its fifty states and the
District of Columbia.

"West Shore" means West Shore Processing Company, L.L.C., a Michigan limited liability company.

"West Shore/Basin Purchase Agreement" means that certain Purchase and Sale Agreement dated as of November 21, 1997, between
Michigan Energy Company and MarkWest Michigan.

"Wholly-Owned Subsidiary" means a Subsidiary of the Borrower of which all of the equity is owned by the Borrower.

SECTION
1.2Use of Defined Terms.Unless otherwise defined or the context otherwise requires, terms for which
meanings are provided in this Agreement shall have such meanings when used in the Disclosure Schedule and in each Note, Borrowing Request, Continuation/Conversion Notice, Loan Document, notice and
other communication delivered from time to time in connection with this Agreement or any other Loan Document.

SECTION
1.3Cross-References.Unless otherwise specified, references in this Agreement and in each other Loan
Document to any Article or Section are references to such Article or Section of this Agreement or such other Loan Document, as the case may be, and, unless otherwise specified,
references in any Article, Section or definition to any clause are references to such clause of such Article, Section or definition.

SECTION
1.4Accounting and Financial Determinations.Unless otherwise specified, all accounting terms used
herein or in any other Loan Document shall be interpreted, all accounting determinations and computations hereunder or thereunder (including under Section 7.2.4) shall be

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made, and all financial statements required to be delivered hereunder or thereunder shall be prepared in accordance with, those U.S. generally accepted accounting principles
("GAAP") applied in the preparation of the financial statements referred to inSection 6.5.

ARTICLE II
REVOLVING LOAN COMMITMENTS, BORROWING PROCEDURES AND NOTES

SECTION
2.1Revolving Loan Commitments.On the terms and subject to the conditions of this Agreement (including Article V), each Lender severally, to the extent of its Percentage, agrees to make Loans pursuant to the Revolving Loan Commitments described in
thisSection 2.1.

SECTION
2.1.1Revolving Loan Commitment.

(a)  On
the terms and subject to the conditions hereof, each Lender severally, but not jointly, agrees to lend to the Borrower such Lender's Percentage of one or more
Borrowings during the Revolving Loan Availability Period, not to exceed such Lender's Percentage of the lesser of (i) the Revolving Loan Commitment Amount and (ii) the Canadian Borrowing
Base.

(b)  Subject
to the conditions set forth in this Agreement, Revolving Loans shall be available during the period beginning on the Effective Date and ending on the day prior
to the Continuation Date (the "Revolving Loan Availability Period").

(c)  On
the terms and subject to the conditions hereof, the Borrower may from time to time borrow and prepay Revolving Loans.

SECTION
2.1.2Commitment to Issue Letters of Credit.From time to time on any Business Day prior to the
Revolving Loan Commitment Termination Date, each Issuer will issue, and each Lender will participate in, to the extent of each Lender's Percentage, the Letters of Credit, in accordance with the terms
ofSection 2.6.

SECTION
2.1.3Global Semi-Annual Borrowing Base Determinations and Allocations.

(a)Global Semi-Annual Borrowing Base and Canadian Borrowing Base Determinations.



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(b)Special Global Semi-Annual Borrowing Base and Canadian Borrowing Base Determinations.



SECTION
2.1.4[Intentionally Blank]

SECTION
2.1.5Lenders Not Required To Make Loans or Issue or Participate in Letters of Credit.No Lender shall
be permitted or required to (a) make any Revolving Loan if, after giving effect thereto, (i) the aggregate outstanding principal amount of all Revolving Loans of all Lenders, together
with all Letter of Credit Outstandings, would exceed the Canadian Borrowing Base; or (ii) the aggregate outstanding principal amount of all Revolving Loans of such Lender, together with its
Percentage of all Letter of Credit Outstandings, would exceed such Lender's Percentage of the Canadian Borrowing Base, or (b) issue (in the case of any Issuer) or participate in (in the case of
each Lender) any Letter of Credit if, after giving effect thereto, (i) all Letter of Credit Outstandings together with the aggregate outstanding principal amount of all Loans of all Lenders
would exceed the

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Canadian Borrowing Base, or (ii) such Lender's Percentage of all Letter of Credit Outstandings together with the aggregate outstanding principal amount of all Loans of such Lender would exceed
such Lender's Percentage of the Canadian Borrowing Base, or (iii) all Letter of Credit Outstandings would exceed the Letter of Credit Sublimit.

SECTION
2.1.6Increase in Revolving Loan Commitment Amount.

(a)  During
the Revolving Loan Availability Period, the Borrower may, by written notice (the "Increase Notice") to the
Canadian Administrative Agent (and the Canadian Administrative Agent shall promptly deliver a copy of such notice to the Lenders), request that the aggregate amount of the Revolving Loan Commitment
Amount be increased by an amount not less than the Canadian Dollar Equivalent of U.S. $5,000,000;provided, that(i) such increase hereunder shall not
exceed the Canadian Dollar Equivalent of U.S. $10,000,000 minusany amount by which the Revolving Loan Commitment Amount shall have been reduced pursuant toSection 2.2, and (ii) after giving effect to such increase, the aggregate amount of the Revolving Loan Commitment Amount hereunder plusthe
aggregate amount of the Revolving Loan Commitment Amount under the U.S. Credit Agreement shall not exceed the Canadian Dollar Equivalent of
U.S. $75,000,000,minusany amount by which the Revolving Loan Commitment Amount under the U.S. Credit Agreement shall have been reduced pursuant to the
provisions of the applicable credit agreement permitting the borrower thereunder to reduce the commitments thereunder. The Increase Notice shall set forth the amount of the requested increase in the
Revolving Loan Commitment Amount and the date on which such increase is requested to become effective (which shall be not less than 30 days or more than 60 days after the date of such
notice) and at the Borrower's option, may offer to one or more existing Lenders and/or other banks or financial institutions (any such Lender or other bank or other institution referred to in this
clause (a) being called an "Augmenting Lender") the opportunity to extend credit hereunder or increase their existing Revolving Loan Commitment
Amount in an aggregate amount equal to the proposed increase;provided,thatno Lender shall be
obligated to agree to increase its Revolving Loan Commitment Amount; andprovided,further, that each
Augmenting Lender, if not already a Lender hereunder, shall be subject to the approval of the Canadian Administrative Agent (which approval shall not be unreasonably withheld) and the Borrower and
each such Augmenting Lender shall execute all such documentation as the Canadian Administrative Agent shall reasonably specify to evidence its Revolving Loan Commitment Amount and status as a Lender
hereunder.

(b)  On
the effective date (the "Increase Effective Date") of any increase in the Revolving Loan Commitment Amount pursuant to
thisSection 2.1.6(the "Commitment Increase"), (i) each Augmenting Lender that shall have
been a Lender prior to the Commitment Increase shall pay to the Canadian Administrative Agent in same day funds an amount equal to the difference between (A) the product of (1) such
Lender's Percentage of the Revolving Loan Commitment (the "Pro Rata Share") (calculated after giving effect to the Commitment Increase) multiplied by(2) the amount of the Post-Continued Loans (as hereinafter defined) and (B) the product of (1) such
Lender's Pro Rata Share (calculated without giving effect to the Commitment Increase)multiplied by(2) the aggregate principal amount of the
Loans outstanding (the "Pre-Continued Loans") immediately prior to giving effect to the Commitment Increase on the Increase Effective Date,
(ii) each Augmenting Lender that shall not have been a Lender prior to the Commitment Increase shall pay to the Canadian Administrative Agent in same day funds an amount equal to the product of
(1) such Augmenting Lender's Pro Rata Share (calculated after giving effect to the Commitment Increase)multiplied by(2) the amount of
the Post-Continued Loans, (iii) after the Canadian Administrative Agent receives the funds specified in clauses (i) and (ii) above, the Canadian Administrative Agent
shall pay to each Lender whose Revolving Loan Commitment is not being increased (a "Non-Increasing Lender") the portion of such funds that
is equal to the difference between (A) the product of (1) such Non-Increasing Lender's Pro Rata Share
(calculated without giving effect to the Commitment Increase)multiplied by(2) the amount of the Pre-Continued Loans and
(B) the product of (1) such Non-Increasing Lender's Pro Rata Share

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(calculated after giving effect to the Commitment Increase)multiplied by(2) the amount of the Post-Continued Loans,
(iv) each Non-Increasing Lender and each Augmenting Lender shall be deemed to hold its Pro Rata Share of each Post-Continued Loan (each calculated after giving effect to
the Commitment Increase) and (v) the Borrower shall pay each Augmenting Lender that shall have been a Lender prior to the Commitment Increase and each Non-Increasing Lender any and
all accrued but unpaid interest on the Pre-Continued Loans up to but not including the Increase Effective Date. As used in thissubsection
(b), "Post-Continued Loans" means, after the effectiveness of the Commitment Increase, Borrowings in an aggregate principal amount equal to the
Pre-Continued Loans and of the types and for the Interest Periods specified in a Borrowing Request delivered to the Canadian Administrative Agent in accordance with Section 2.3.

(c)  Increases
and new Revolving Loan Commitment Amount created pursuant to thisSection 2.1.6shall become effective
on the date specified in the notice delivered by the Borrower pursuant to the first sentence ofparagraph (a)above.

(d)  No
increase in the total Revolving Loan Commitment Amount (or in the Revolving Loan Commitment of any Lender) or addition of a new Lender shall become effective under
this Section unless (i) the Borrower shall deliver a certificate of an Authorized Officer, dated as of the Increase Effective Date, certifying that no Default shall have occurred and be
continuing and that the representations and warranties of the Borrower contained in this Agreement are true and correct on and as of such date, and (ii) the Canadian Administrative Agent shall
have received documents and an opinion consistent with those delivered on the Effective Date underSections 5.1.1and 5.1.6as to the corporate authority
of the Borrower to continue to borrow hereunder after giving effect to such increase.

(e)  Notwithstanding
the foregoing, no increase in the Revolving Loan Commitment Amount may be made pursuant to this Section 2.1.6unless, after such increase, the Percentage of each Lender hereunder is the same as the
pro rata share of such Lender or its
Affiliate under the U.S. Credit Agreement.

SECTION
2.2Optional Reduction of Revolving Loan Commitment Amount.The Borrower may, from time to time on any
Business Day, voluntarily reduce the Revolving Loan Commitment Amount;provided,however, that all such
reductions shall require at least three Business Days' prior notice to the Canadian Administrative Agent and be permanent, and any partial reduction of any Revolving Loan Commitment Amount shall be in
a minimum amount of Cdn. $2,500,000, and greater integral multiples of Cdn. $500,000.

SECTION
2.3Borrowing Procedure.By delivering a Borrowing Request to the Canadian Administrative Agent on or
before 12:00 p.m. (noon), Toronto, Ontario time, on a Business Day, the Borrower may from time to time irrevocably request, (a) on not less than three nor more than five Business Days'
notice, a LIBO Rate Loan, or (ii) on not less than two Business Days' or more than five Business Days' notice, a Canadian Prime Rate Loan in a minimum amount of Cdn. $1,000,000 and greater
integral multiples of Cdn. $500,000, or in the unused amount of the applicable Revolving Loan Commitment, if less. On the terms and subject to the conditions of this Agreement, each Borrowing shall be
comprised of the type of Loans, and shall be made on the Business Day specified in such Borrowing Request. On or before 11:00 a.m., Toronto, Ontario time, on such specified Business Day each
Lender shall deposit with the Canadian Administrative Agent same day funds in an amount equal to such Lender's Percentage of the requested Borrowing. Such deposit will be made to an account which the
Canadian Administrative Agent shall specify from time to time by notice to the Lenders. To the extent funds are received from the Lenders, the Canadian Administrative Agent shall make such funds
available to the Borrower by wire transfer to the accounts the Borrower shall have specified in its Borrowing Request. No Lender's obligation to make any Loan shall be affected by any other Lender's
failure to make any Loan.

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(b)  Canadian Prime Rate Loans and LIBO Rate Loans shall be funded in Canadian Dollars.

SECTION
2.4Continuation and Conversion Elections.By delivering a Continuation/Conversion Notice to the
Canadian Administrative Agent on or before 12:00 p.m. (noon), Toronto, Ontario time, on a Business Day, the Borrower may from time to time irrevocably elect, (a) on not less than three
nor more than five Business Days' notice, in connection with any LIBO Rate Loan or any Canadian Prime Rate Loan that all, or any portion in an aggregate minimum amount of Cdn. $1,000,000, and greater
integral multiples of Cdn. $500,000, of any Loans be, in the case of Canadian Prime Rate Loans, converted into LIBO Rate Loans or, in the case of LIBO Rate Loans, be continued as a LIBO Rate Loan, and
(b) on or before one (1) Business Day prior to the last day of the then current Interest Period with respect to a LIBO Rate Loan, that such Loan be converted into a Canadian Prime Rate
Loan (in the absence of delivery of a Continuation/Conversion Notice with respect to any LIBO Rate Loan at least three Business Days before the last day of the then current Interest Period with
respect thereto, such LIBO Rate Loan shall, on such last day, automatically convert to a Canadian Prime Rate Loan);provided, however, that (x) each
such conversion or continuation shall be pro rated among the applicable outstanding Loans of all Lenders, and
(y) no portion of the outstanding principal amount of any Loans may be continued as, or be converted into, LIBO Rate Loans when any Default has occurred and is continuing. A continuation or
conversion shall not be considered a new Loan or Borrowing hereunder.

SECTION
2.5Notes.

(a)  The
Loans made by, and the Borrower's Reimbursement Obligations to, each Lender shall be evidenced by one or more accounts or records maintained by such Lender and by
the Canadian Administrative Agent in the ordinary course of business. The accounts or records maintained by the Canadian Administrative Agent and each Lender shall be prima facie evidence of the Loans
and the Borrower's Reimbursement Obligations, absent manifest error. Any failure so to record or any error in doing so shall not, however, limit or otherwise affect the obligation of the Borrower
hereunder to pay any amount owing with respect to the Loans and Letters of Credit. In addition to such accounts or records, each Lender's Loans may be evidenced by a Note substantially in the form of Exhibit Ahereto. Each Lender may attach schedules to its Note(s) and endorse thereon the date, amount and maturity of the applicable Loans and
payments with respect thereto.

(b)  In
addition to the accounts and records referred to insubsection (a), each Lender and the Canadian Administrative Agent
shall maintain in accordance with its usual practice accounts or records evidencing the purchases and sales by such Lender of participations in Letters of Credit. In the event of any conflict between
the accounts and records maintained by the Canadian Administrative Agent
and the accounts and records of any Lender in respect of such matters, the accounts and records of the Canadian Administrative Agent shall control.

SECTION
2.6Letters of Credit.

SECTION
2.6.1Issuance Requests.By delivering to the Canadian Administrative Agent and the applicable Issuer an
Issuance Request on or before 11:30 a.m., Toronto, Ontario time, the Borrower may request, from time to time prior to the Revolving Loan Commitment Termination Date and on not less than three
nor more than ten Business Days' notice, that such Issuer issue an irrevocable standby letter of credit in such form as may be mutually agreed to by the Borrower and such Issuer (each a
"Letter of Credit"), in support of financial and performance obligations of the Borrower incurred in the Borrower's ordinary course of business and
which are described in such Issuance Request. Upon receipt of an Issuance Request, the Canadian Administrative Agent shall promptly notify the Lenders thereof. Each Letter of Credit shall by its
terms: (a) be issued in a Stated Amount which (i) together with all Letter of Credit Outstandings does not exceed the Letter of Credit Sublimit, or (ii) together with all Letter
of Credit Outstandings and all outstanding Loans does not exceed (or would not exceed) the Canadian Borrowing Base as of such date; and (b) be stated to expire on a date (its
"Stated Expiry

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Date") no later than the earlier of (i) one year from its date of issuance and (ii) the Revolving Loan Commitment Termination Date. So long as no Default has
occurred and is continuing, by delivery to the applicable Issuer and the Canadian Administrative Agent of an Issuance Request at least three but not more than ten Business Days prior to the Stated
Expiry Date of any Letter of Credit, the Borrower may request such Issuer to extend the Stated Expiry Date of such Letter of Credit for an additional period not to exceed the earlier of one year from
its date of extension and the Revolving Loan Commitment Termination Date.

SECTION
2.6.2Issuances and Extensions.On the terms and subject to the conditions of this Agreement (including Article V), the Issuer shall issue Letters of Credit, and extend the Stated Expiry Dates of outstanding Letters of Credit, in accordance with the
Issuance Requests made therefor. Each Issuer will make available the original of each Letter of Credit which it issues in accordance with the Issuance Request therefor to the beneficiary thereof (and
will promptly provide each of the Lenders and the Borrower with a copy of such Letter of Credit) and will notify the beneficiary under any Letter of Credit of any extension of the Stated Expiry Date
thereof.

SECTION
2.6.3Other Lenders' Participation.Each Letter of Credit issued pursuant to Section 2.6.2shall,
effective upon its issuance and without further action, be issued on behalf of all Lenders (including the Issuer thereof) pro rataaccording to their respective Percentages. Each Lender shall, to the
extent of its Percentage, be deemed irrevocably to have participated in
the issuance of such Letter of Credit and shall be responsible to reimburse promptly the Issuer thereof for Reimbursement Obligations which have not been reimbursed by the Borrower in accordance with Section 2.6.5, or which have been reimbursed by the Borrower but must be returned, restored or disgorged by such Issuer for any reason, and each
Lender shall, to the extent of its Percentage, be entitled to receive from the Canadian Administrative Agent a ratable portion of the letter of credit fees received by the Canadian Administrative
Agent pursuant toSection 3.3.3, with respect to each Letter of Credit. In the event that
the Borrower shall fail to reimburse any Issuer, or if for any reason Loans shall not be made to fund any Reimbursement Obligation, all as provided in Section 2.6.5and in an amount equal to the
amount of any drawing honored by such Issuer under a Letter of Credit issued by it, or in the event
such Issuer must for any reason return or disgorge such reimbursement, such Issuer shall promptly notify each Lender of the unreimbursed amount of such drawing and of such Lender's respective
participation therein. Each Lender shall make available to such Issuer, whether or not any Default shall have occurred and be continuing, an amount equal to its respective participation in same day or
immediately available funds at the office of such Issuer specified in such notice not later than 11:30 a.m., Toronto, Ontario time, on the Business Day (under the laws of the jurisdiction of
such Issuer) after the date notified by such Issuer. In the event that any Lender fails to make available to such Issuer the amount of such Lender's participation in such Letter of Credit as provided
herein, such Issuer shall be entitled to recover such amount on demand from such Lender together with interest at the daily average Federal Funds Rate for three Business Days (together with such other
compensatory amounts as may be required to be paid by such Lender to the Canadian Administrative Agent pursuant to the Rules for Interbank Compensation of the council on International Banking or the
Clearinghouse Compensation Committee, as the case may be, as in effect from time to time) and thereafter at the Canadian Prime Rateplus2%. Nothing in
this Section shall be deemed to prejudice the right of any Lender to recover from any Issuer any amounts made available by such Lender to such Issuer pursuant to this Section in the event that it is
determined by a court of competent jurisdiction that the payment with respect to a Letter of Credit by such Issuer in respect of which payment was made by such Lender constituted gross negligence or
wilful misconduct on the part of such Issuer. Each Issuer shall distribute to each other Lender which has paid all amounts payable by it under this Section with respect to any Letter of Credit issued
by such Issuer such other Lender's Percentage of all payments received by such Issuer from the Borrower in reimbursement of drawings honored by such Issuer under such Letter of Credit when such
payments are received.

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SECTION
2.6.4Disbursements.Each Issuer will notify the Borrower and the Canadian Administrative Agent promptly
of the presentment for payment of any Letter of Credit, together with notice of the date (the "Disbursement Date") such payment shall be made. Subject
to the terms and provisions of such Letter of Credit, the applicable Issuer shall make such payment to the beneficiary (or its designee) of such Letter of Credit. Prior to 11:30 a.m., Toronto,
Ontario time, on the Disbursement Date, the Borrower will reimburse the applicable Issuer for all amounts which it has disbursed under the Letter of Credit. In the event the applicable Issuer is not
reimbursed by the Borrower on the Disbursement Date, or if such Issuer must for any reason return or disgorge such reimbursement, the Lenders (including such Issuer) shall, on the terms and subject to
the conditions of this Agreement, fund the Reimbursement Obligation therefor by making, on the next Business Day, Loans which are Canadian Prime Rate Loans, as provided in Section 2.1(the Borrower
being deemed to have given a timely Borrowing Request therefor for such amount); provided,however, that for the purpose of determining the availability of
the Revolving Loan
Commitments to make Loans immediately prior to giving effect to the application of the proceeds of such Loans, such Reimbursement Obligation shall be deemed not to be outstanding at such time. To the
extent the applicable Issuer is not reimbursed in full in accordance with the preceding sentences, the Borrower's Reimbursement Obligation shall accrue interest at a fluctuating rate equal to the
Canadian Prime Rateplusthe Applicable Marginplusa margin of 2% per annum, payable on demand.

SECTION
2.6.5Reimbursement.The Borrower's obligation (a "Reimbursement
Obligation") underSection 2.6.4to reimburse an Issuer with respect to each Disbursement (including interest thereon),
and each Lender's obligation to make participation payments in each drawing which has not been reimbursed by the Borrower, shall be absolute and unconditional under any and all circumstances and
irrespective of any setoff, counterclaim, or defense to payment which the Borrower may have or have had against any Lender or any beneficiary of a Letter of Credit, including any defense based upon
the occurrence of any Default, any draft, demand or certificate or other document presented under a Letter of Credit proving to be forged, fraudulent, invalid or insufficient, the failure of any
disbursement to conform to the terms of the applicable Letter of Credit (if, in the applicable Issuer's good faith opinion, such disbursement is determined to be appropriate) or any
non-application or misapplication by the beneficiary of the proceeds of such disbursement, or the legality, validity, form, regularity, or enforceability of such Letter of Credit; provided,however, that nothing herein shall adversely affect the right of the Borrower or any Lender to
commence any proceeding against the applicable Issuer for any wrongful disbursement made by such Issuer under a Letter of Credit as a result of acts or omissions constituting gross negligence or
wilful misconduct on the part of such Issuer.

SECTION
2.6.6Deemed Disbursements.Upon either (a) the occurrence and during the continuation of an
Event of Default pursuant toSection 8.1.9or the occurrence of the Revolving Loan Commitment Termination Date or (b) the declaration by
the Canadian Administrative Agent of all or any portion of the outstanding principal amount of the Loans and other Obligations to be due and payable and/or the Revolving Loan Commitments (if not
theretofore terminated) to be terminated as provided inSection 8.3, an amount equal to that portion of Letter of Credit Outstandings
attributable to outstanding and undrawn Letters of Credit shall, at the election of the applicable Issuer acting on instructions from the Required Lenders, and without demand upon or notice to the
Borrower, be deemed to have been paid or disbursed by such Issuer under such Letters of Credit (notwithstanding that such amount may not in fact have been so paid or disbursed), and, upon notification
by such Issuer to the Canadian Administrative Agent and the Borrower of its obligations under this Section, the Borrower shall be immediately obligated to reimburse such Issuer the amount deemed to
have been so paid or disbursed by such Issuer. Any amounts so received by such Issuer from the Borrower pursuant to this Section shall be held as collateral security for the repayment of the
Borrower's obligations in connection with the Letters of Credit issued by such Issuer. All amounts on deposit pursuant to thisSection 2.6.6shall, until their application to any Obligation or their return to the Borrower, as the case may be, at the Borrower's written request, be invested in high grade short-term liquid
investments

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acceptable to Canadian Administrative Agent and designated by the Borrower, which investments shall be held by the Canadian Administrative Agent as additional collateral security for the repayment of
the Borrower's Obligations under and in connection with the Letters of Credit and all other Obligations. Any losses, net of earnings, and reasonable fees and expenses of such investments shall be
charged against the principal amount invested. The Canadian Administrative Agent and the Lenders shall not be liable for any loss resulting from any investment made by the Canadian Administrative
Agent at the Borrower's request. The Canadian Administrative Agent is not obligated hereby, or by any other Loan Document, to make or maintain any investment, except upon written request by the
Borrower. At any time when such Letters of Credit shall terminate and all Obligations to each Issuer are either terminated or paid or reimbursed to such Issuer in full, the Obligations of the Borrower
under this Section shall be reduced accordingly (subject, however, to reinstatement in the event any payment in respect of such Letters of Credit is recovered in any manner from such Issuer), and such
Issuer will return to the Borrower the excess, if any, of (x) the aggregate amount held by such Issuer and not theretofore applied by such Issuer to any Reimbursement Obligation over(y) the
aggregate amount of all Reimbursement Obligations to such Issuer pursuant to this Section, as so adjusted. At such time when all
Events of Default shall have been cured or waived, if the Revolving Loan Commitment
Termination Date shall not have occurred for any reason, each Issuer shall return to the Borrower all amounts then on deposit with such Issuer pursuant to this Section.

SECTION
2.6.7Nature of Reimbursement Obligations.The Borrower shall assume all risks of the acts, omissions,
or misuse of any Letter of Credit by the beneficiary thereof. Neither any Issuer nor any Lender (except to the extent of its own gross negligence or wilful misconduct) shall be responsible for:
(a) the form, validity, sufficiency, accuracy, genuineness, or legal effect of any Letter of Credit or any document submitted by any party in connection with the application for and issuance of
a Letter of Credit, even if it should in fact prove to be in any or all respects invalid, insufficient, inaccurate, fraudulent, or forged; (b) the form, validity, sufficiency, accuracy,
genuineness, or legal effect of any instrument transferring or assigning or purporting to transfer or assign a Letter of Credit or the rights or benefits thereunder or proceeds thereof in whole or in
part, which may prove to be invalid or ineffective for any reason; (c) failure of the beneficiary to comply fully with conditions required in order to demand payment under a Letter of Credit;
(d) errors, omissions, interruptions, or delays in transmission or delivery of any messages, by mail, cable, telegraph, telex, facsimile or otherwise; or (e) any loss or delay in the
transmission or otherwise of any document or draft required in order to make a Disbursement under a Letter of Credit or of the proceeds thereof. None of the foregoing shall affect, impair, or prevent
the vesting of any of the rights or powers granted any Issuer or any Lender hereunder. In furtherance and extension, and not in limitation or derogation, of any of the foregoing, any action taken or
omitted to be taken by any Issuer in good faith shall be binding upon the Borrower and shall not put such Issuer under any resulting liability to the Borrower.

SECTION
2.6.8Increased Costs; Indemnity.If by reason of (a) any change in applicable law, regulation,
rule, decree or regulatory requirement or any change in the interpretation or application by any judicial or regulatory authority of any law, regulation, rule, decree or regulatory requirement, or
(b) compliance by any Issuer or any Lender with any direction, or requirement of any governmental or monetary authority, including Regulation D of the F.R.S. Board: (i) any Issuer
or any Lender shall be subject to any tax (other than taxes on net income and franchises), levy, charge or withholding of any nature or to any variation thereof or to any penalty with respect to the
maintenance or fulfillment of its obligations under thisSection 2.6, whether directly or by such being imposed on or suffered by such Issuer or
such Lender; (ii) any reserve, deposit or similar requirement is or shall be applicable, increased, imposed or modified in respect of any Letters of Credit issued by any Issuer or
participations therein purchased by any Lender; or (iii) there shall be imposed on any Issuer or any Lender any other condition regarding this Section 2.6, any Letter of Credit or any
participation therein, and the result of the foregoing is directly to increase the cost to such Issuer
or such Lender of issuing or maintaining any Letter of Credit or of purchasing or maintaining any participation therein, or to

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reduce any amount receivable in respect thereof by such Issuer or such Lender, then and in any such case such Issuer or such Lender may, at any time after the additional cost is incurred or the
amount received is reduced, notify the Canadian Administrative Agent and the Borrower thereof, and the Borrower shall pay within 10 days of demand such amounts as such Issuer or Lender may in
good faith specify to be necessary to compensate such Issuer or Lender for such additional cost or reduced receipt, together with interest on such amount from the date demanded until payment in full
thereof at a rate equal at all times to the Canadian Prime Rate. The determination by such Issuer or Lender, as the case may be, of any amount due pursuant to this Section, as set forth in a statement
setting forth the calculation thereof in reasonable detail, shall be rebuttable presumptive evidence of such amounts.

In
addition to amounts payable as elsewhere provided in thisSection 2.6, the Borrower hereby indemnifies, exonerates and holds
each Issuer, the Canadian Administrative Agent and each Lender harmless from and against any and all actions, causes of action, suits, losses, costs, liabilities and damages, and expenses incurred in
connection therewith (irrespective of whether such Issuer, the Canadian Administrative Agent or such Lender is a party to the action for which indemnification is sought), including reasonable
attorneys' fees and disbursements, which such Issuer, the Canadian Administrative Agent or such Lender may incur or be subject to as a consequence, direct or indirect, of the issuance of the Letters
of Credit, other than as a result of the gross negligence or wilful misconduct of such Issuer as determined by a court of competent jurisdiction, or the failure of such Issuer to honor a drawing under
any Letter of Credit as a result of any act or omission, whether rightful or wrongful, of any present or future de jure or de facto government or governmental authority.

ARTICLE III
REPAYMENTS, PREPAYMENTS, INTEREST AND FEES

SECTION
3.1Repayments and Prepayments.The Borrower shall repay in full the unpaid principal amount of each
Loan upon the Stated Maturity Date therefor. Each prepayment of any Loans made pursuant to this Section shall be without premium or penalty, except as may be required by Section 4.4. No voluntary
prepayment of principal of any Revolving Loan shall cause a reduction in the Revolving Loan Commitment Amount, except
as provided inSection 2.2.

SECTION
3.1.1Optional Prepayment.At any time prior to the Stated Maturity Date, the Borrower may, from time to
time on any Business Day, make a voluntary prepayment, in whole or in part, of the outstanding principal amount of any Loans;provided, however, that
(a) any such prepayment shall be madepro rataamong Loans of the same type and, if
applicable, having the same Interest Period of all Lenders, (b) no such prepayment of any LIBO Rate Loan may be made on any day other than the last day of the Interest Period for such Loan,
(c) all such voluntary prepayments (i) of LIBO Rate Loans, shall require at least three (3) Business Days' prior written notice to the Canadian Administrative Agent, and
(ii) of Canadian Prime Rate Loans, shall require at least one (1) Business Day's prior written notice to the Canadian Administrative Agent, and (d) all such voluntary partial
prepayments shall be in an aggregate minimum amount of Cdn. $1,000,000, and greater integral multiples of Cdn. $500,000.

SECTION
3.1.2Mandatory Prepayment.

(a)  The
provisions of this subparagraph (a) shall apply so long as the U.S. Credit Agreement is in effect. Unless otherwise directed by the Global Lenders (as defined
in the U.S. Credit Agreement), if on any date the sum of the U.S. Dollar Equivalent of the Canadian Effective Amount and the U.S. Effective Amount shall exceed the Global Borrowing Base, and no
additional mandatory prepayments are made pursuant toSection 3.1.2of the U.S. Credit Agreement to remedy any remaining excess
("Unremedied Excess"), then the Borrower shall make mandatory prepayments of Loans equal to such Unremedied
Excess, and if any such Unremedied Excess remains after such prepayments, to the extent of such Unremedied Excess the Borrower shall immediately Cash Collateralize the Reimbursement

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Obligations in an amount equal to the aggregate Stated Amount of all Letters of Credit outstanding and undrawn. The Borrower shall make fifty percent (50%) of such payments within ninety
(90) days following its receipt of the written notice of the Global Borrowing Base and Canadian Borrowing Base redetermination in accordance with Section 2.1.3(a)(ii)of the U.S. Credit
Agreement, and the remaining fifty percent (50%) of such prepayments within one hundred eighty
(180) days following its receipt of the notice of the relevant redetermination.

(b)  If
on any date the U.S. Credit Agreement is not effective and the Canadian Effective Amount shall exceed the Canadian Borrowing Base, then the Borrower shall make
mandatory prepayments of Loans equal to such excess, and if any such excess remains after such prepayments, to the extent of such excess the Borrower shall immediately Cash Collateralize the
Reimbursement Obligations in an amount equal to the aggregate Stated Amount of all Letters of Credit outstanding and undrawn. The Borrower shall be obligated to (A) make fifty percent (50%) of
such prepayments within ninety (90) days following its receipt of the written notice of the Canadian Borrowing Base redetermination in accordance with Section 2.1.3(a)(ii), and the remaining
fifty percent (50%) of such prepayments within one hundred eighty (180) days following its receipt
of notice of the relevant redetermination, or (B) make such prepayment on the date of any Sale which results in a reduction in the Canadian Borrowing Base pursuant to Section 7.2.9(b).

(c)  During
the Revolving Loan Availability Period, Loans prepaid pursuant to thisSection 3.1.2may be
re-borrowed to the extent the Canadian Borrowing Base subsequently is re-determined to a level that would allow such re-borrowing and the conditions to Borrowing
hereunder have been satisfied.

SECTION
3.1.3Mandatory Prepayment on Acceleration.The Borrower shall, immediately upon any acceleration of the
Stated Maturity Date of any Loans pursuant toSection 8.2orSection 8.3, repay all Loans,
unless, pursuant toSection 8.3, only a portion of all Loans is so accelerated.

SECTION
3.2Interest Provisions.Interest on the outstanding principal amount of Loans shall accrue and be
payable in accordance with thisSection 3.2.

SECTION
3.2.1Rates.Pursuant to an appropriately delivered Borrowing Request or Continuation/Conversion Notice,
the Borrower may elect that Loans comprising a Borrowing accrue interest at a rate per annum: (a) on that portion maintained from time to time as a Canadian Prime Rate Loan, equal to the
Canadian Prime Rateplusthe Applicable Margin from time to time in effect; and (b) on that portion maintained as a LIBO Rate Loan, during each
Interest Period applicable thereto, equal to the sum of the LIBO Rate (Reserve Adjusted) for such Interest Periodplusthe Applicable Margin.

All
LIBO Rate Loans shall bear interest from and including the first day of the applicable Interest Period to (but not including) the last day of such Interest Period at the interest
rate determined as applicable to such LIBO Rate Loan.

SECTION
3.2.2Default Rate.While any Event of Default exists or after acceleration, the Borrower shall pay upon
demand interest (after as well as before judgment) on the principal amount of all outstanding Obligations at a fluctuating rate per annum equal to the Canadian Prime Rate plusthe Applicable Marginplus2%;provided, however, that with respect to a LIBO Rate Loan, the Default Rate shall be an interest
rate equal to the interest rate (including any Applicable Margin)
otherwise applicable to such Loanplus2% per annum, but in any event not to exceed the maximum rate permitted by applicable law.

SECTION
3.2.3Payment Dates.Interest accrued on each Loan shall be payable, without duplication: (a) on
the Stated Maturity Date therefor; (b) on the date of any payment or prepayment, in whole or in part, of principal outstanding on such Loan; (c) with respect to Canadian Prime Rate
Loans, on each Quarterly Payment Date occurring after the Effective Date; (d) with respect to LIBO

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Rate Loans, the last day of each applicable Interest Period (and, if such Interest Period shall exceed 90 days, on the 90th day of such Interest Period); (e) with respect to any
Canadian Prime Rate Loans converted into LIBO Rate Loans on a day when interest would not otherwise have been payable pursuant toclause (c), on
the date of such conversion; and (f) on that portion of any Loans the Stated Maturity Date of which is accelerated pursuant toSection 8.2orSection 8.3, immediately upon such acceleration. Interest accrued on Loans or other monetary Obligations arising under this Agreement or any
other Loan Document after the date such amount is due and payable (whether on the Stated Maturity Date, upon acceleration or otherwise) shall be payable upon demand.

SECTION
3.2.4[Intentionally Blank]

SECTION
3.3Fees.The Borrower agrees to pay the fees set forth in this Section 3.3. All such fees shall be
non-refundable.

SECTION
3.3.1Commitment Fee.The Borrower agrees to pay to the Canadian Administrative Agent for the account of
each Lender, for the period (including any portion thereof when any of its Revolving Loan Commitments are suspended by reason of the Borrower's inability to satisfy any condition of Article V)
commencing on the Effective Date and continuing through the final Revolving Loan Commitment Termination Date, a Commitment Fee on such
Lender's Percentage of the sum of the average daily unused portion of the Revolving Loan Commitment Amount (outstanding Loans and Letters of Credit being deemed to be usage hereunder). Such Commitment
Fee shall be payable by the Borrower in arrears, on each Quarterly Payment Date, commencing with the first such day following the Effective Date, and on the Revolving Loan Commitment Termination Date.

SECTION
3.3.2Canadian Administrative Agent's Fees.(a) The Borrower agrees to pay the fees provided in
the fee letter dated August 10, 2001 between the Borrower, the Canadian Administrative Agent and Banc of America Securities LLC;

(b)  If
the U.S. Credit Agreement is not effective, the Borrower shall pay to the Administrative Agent, an annual engineering fee, in the amount of $5,000 on each
March 1, commencing March 1, 2003, until the Stated Maturity Date.

SECTION
3.3.3Letter of Credit Fees.(a) The Borrower agrees to pay to the Canadian Administrative Agent,
for the account of each Lender, a fee for each Letter of Credit for the period from and including the date of the issuance of such Letter of Credit to (but not including) the date upon which such
Letter of Credit expires, at a per annum rate equal to the Applicable Margin on the outstanding face amount of each Letter of Credit. Such fee shall be payable by the Borrower in arrears on each
Quarterly Payment Date, and on the Revolving Loan Commitment Termination Date for any period then ending for which such fee shall not theretofore have been paid, commencing on the first such date
after the issuance of such Letter of Credit.

(b)  The
Borrower agrees to pay to the Canadian Administrative Agent, for the account of the Issuer, (i) a Letter of Credit fronting fee for each Letter of Credit upon
the issuance of each Letter of Credit in an amount equal to the greater of (A) Cdn. $500 or (B) one-eight of one percent (1/8 of 1%) calculated on the face
amount thereof, and (ii) such Issuer's standard drawing fees and other processing fees upon any drawing under such Letter of Credit.

ARTICLE IV  CERTAIN LIBO RATE AND OTHER PROVISIONS

SECTION
4.1Fixed Rate Lending Unlawful.If any Lender shall determine (which determination shall, upon notice
thereof to the Borrower and the Lenders, be conclusive and binding on the Borrower) that the introduction of or any change in or in the interpretation of any law makes it unlawful, or any central bank
or other governmental authority asserts that it is unlawful, for such Lender to make, continue or maintain any Loan as, or to convert any Loan into, a LIBO Rate Loan of

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a certain type, the obligations of all Lenders to make, continue, maintain or convert any such Loans shall, upon such determination, forthwith be suspended until such Lender shall notify the Canadian
Administrative Agent that the circumstances causing such suspension no longer exist, and all LIBO Rate Loans of such type shall automatically convert into Canadian Prime Rate Loans at the end of the
then current Interest Periods with respect thereto or sooner, if required by such law or assertion.

SECTION
4.2Deposits Unavailable.If the Canadian Administrative Agent shall have determined that
(a) Cdn. Dollar deposits in the relevant amount and for the relevant Interest Period are not available to the Lenders in their relevant markets; or (b) by reason of circumstances
affecting BofA Canada's relevant market, adequate means do not exist for ascertaining the interest rate applicable hereunder to LIBO Rate Loans, then, upon notice from the Canadian Administrative
Agent to the Borrower and the Lenders, the obligations of all Lenders underSection 2.3and Section 2.4to make or continue any Loans as, or to
convert any Loans into, LIBO Rate Loans shall forthwith be suspended until the Canadian
Administrative Agent shall notify the Borrower and the Lenders that the circumstances causing such suspension no longer exist.

SECTION
4.3Increased LIBO Rate Loan Costs, etc.The Borrower agrees to reimburse each Lender for any increase
in the cost to such Lender of, or any reduction in the amount of any sum receivable by such Lender in respect of, making, continuing or maintaining (or of its obligation to make, continue or maintain)
any Loans as, or of converting (or of its obligation to convert) any Loans into, LIBO Rate Loans. Such Lender shall promptly notify the Canadian Administrative Agent and the Borrower in writing of the
occurrence of any such event, such notice to state, in reasonable detail, the reasons therefor and the additional amount required fully to compensate such Lender for such increased cost or reduced
amount; provided, that no Lender shall give such notice unless it is generally charging borrowers similarly situated to the Borrower with similar agreements with such Lender such amounts. Such
additional amounts shall be payable by the Borrower directly to such Lender within five days of its receipt of such notice, and such notice shall be rebuttable presumptive evidence of such amounts.

SECTION
4.4Funding Losses.In the event any Lender shall incur any loss, cost or expense as a result of
(a) any conversion or repayment or prepayment of the principal amount of any LIBO Rate Loans on a date other than the scheduled last day of the Interest Period applicable thereto, whether
pursuant to Section 3.1 or otherwise; (b) any Loans not being made as LIBO Rate Loans or Canadian Prime Rate Loan in accordance with the Borrowing Request therefor; or (c) any
Loans not being continued as, or converted into, LIBO Rate Loans in accordance with the Continuation/ Conversion Notice therefor, then, upon the written notice of such Lender to the Borrower (with a
copy to the Canadian Administrative Agent), the Borrower shall, within five days of its receipt thereof, pay directly to such Lender such amount as will (in the reasonable determination of such
Lender) reimburse such Lender for such loss, cost or expense. Such written notice (which shall include calculations in reasonable detail) and shall be rebuttable presumptive evidence of such amounts.
The amounts calculated pursuant to this Section 4.4 shall include any loss, cost or expense incurred by a Lender in connection with any foreign exchange agreement, and any loss, cost or expense
incurred by reason of the liquidation or reemployment of deposits or other funds acquired by such Lender to make, continue or maintain any portion of the principal amount of any Loan as, or to convert
any portion of the principal amount of any Loan into, a LIBO Rate Loan.

SECTION
4.5Increased Capital Costs.If any change in, or the introduction, adoption, effectiveness,
interpretation, reinterpretation or phase-in of, any law or regulation, directive, guideline, decision or request of any court, central bank, regulator or other governmental authority
affects or would affect the amount of capital required or expected to be maintained by any Lender or any Person controlling such Lender, and such Lender determines (in its discretion exercised in good
faith) that the rate of return on its or such controlling Person's capital as a consequence of its Revolving Loan Commitments or the Loans made by such Lender is reduced to a level below that which
such Lender

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or such controlling Person could have achieved but for the occurrence of any such circumstance, then, in any such case upon notice from time to time by such Lender to the Borrower, the Borrower shall
immediately pay directly to such Lender additional amounts sufficient to compensate such Lender or such controlling Person for such reduction in rate of return. A statement of such Lender as to any
such additional amount or amounts shall be furnished to Borrower including calculations thereof in reasonable detail and shall be rebuttable presumptive evidence of such amounts. In determining such
amount, such Lender may use any method of averaging and attribution that it (in its discretion exercised in good faith) shall deem applicable.

SECTION
4.6Taxes.All payments by the Borrower of principal of, and interest on, the Loans, all payments in
respect of the Reimbursement Obligations and all other amounts payable hereunder shall be made free and clear of and without deduction for any present or future excise, stamp or franchise taxes and
other taxes, fees, duties, withholdings or other charges of any nature whatsoever imposed by any taxing authority, but excluding franchise taxes and taxes imposed on or measured by any Lender's net
income or receipts by the jurisdiction (or any political subdivision thereof) under the laws of which such Lender is organized or maintains an office from which Loans are funded (such
non-excluded items being called "Taxes"). In the event that any withholding or deduction from any payment to be made by the Borrower
hereunder is required in respect of any Taxes pursuant to any applicable law, rule or regulation, then the Borrower will (a) pay directly to the relevant authority the full amount required to
be so withheld or deducted; (b) promptly forward to the Canadian Administrative Agent an official receipt or other documentation satisfactory to the Canadian Administrative Agent evidencing
such payment to such authority; and (c) pay to the Canadian Administrative Agent for the account of the Lenders such additional amount or amounts as is necessary to ensure that the net amount
actually received by each Lender will equal the full amount such Lender would have received had no such withholding or deduction been required. Moreover, if any Taxes are directly asserted against the
Canadian Administrative Agent or any Lender with respect to any payment received by the Canadian Administrative Agent or such Lender hereunder, the Canadian Administrative Agent or such Lender may pay
such Taxes and the Borrower will promptly pay such additional amounts (including, if incurred as a result of the Borrower's action, omission or delay, any penalties, interest or expenses) as is
necessary in order that the net amount received by such person after the payment of such Taxes (including any Taxes on such additional amount) shall equal the amount such person would have received
had not such Taxes been asserted.

If
the Borrower fails to pay any Taxes when due to the appropriate taxing authority or fails to remit to the Canadian Administrative Agent, for the account of the respective Lenders, the
required receipts or other required documentary evidence, the Borrower shall indemnify the Lenders for any incremental Taxes, interest or penalties that may become payable by any Lender as a result of
any failure of Borrower to pay the taxing authorities directly where required. For purposes of thisSection 4.6, a distribution hereunder by the
Canadian Administrative Agent or any Lender to or for the account of any Lender shall be deemed a payment by the Borrower.

SECTION
4.7Payments, Computations, etc.Unless otherwise expressly provided, all payments by the Borrower
pursuant to this Agreement, the Notes or any other Loan Document shall be made by the Borrower to the Canadian Administrative Agent for thepro rataaccount of the Lenders entitled to receive such payment. All such payments required to be made to the Canadian Administrative Agent
shall be made, without setoff, deduction or counterclaim, not later than 11:00 a.m., Toronto, Ontario time, on the date due, in same day or immediately available funds, to such account as the
Canadian Administrative Agent shall specify from time to time by notice to the Borrower. Funds received after that time shall be deemed to have been received by the Canadian Administrative Agent on
the next succeeding Business Day. The Canadian Administrative Agent shall promptly remit in same day funds to each Lender its share, if any, of such payments received by the Canadian Administrative
Agent for the account of such Lender. All interest and fees shall be computed on the basis of the actual number

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of days (including the first day but excluding the last day) occurring during the period for which such interest or fee is payable over a year comprised of 360 days (which results in more
interest being paid than if computed on the basis of a 365-day year) or, in the case of interest on a Canadian Prime Rate Loan, 365 days or, if appropriate, 366 days.
Whenever any payment to be made shall otherwise be due on a day which is not a Business Day, such payment shall (except as otherwise required by clause (c)of the definition of the term
"Interest Period" with respect to LIBO Rate Loans) be
made on the next succeeding Business Day and such extension of time shall be included in computing interest and fees, if any, in connection with such payment. Each rate of interest which is calculated
with reference to a period (the "deemed interest period") that is less than the actual number of days in the calendar year of calculation is, for the
purposes of the Interest Act (Canada), equivalent to a rate based on a calendar year calculated by multiplying such rate of interest by the actual number of days in the calendar year of calculation
and dividing by the number of days in the deemed interest period.

SECTION
4.8Sharing of Payments.If any Lender shall obtain any payment or other recovery (whether voluntary,
involuntary, by application of setoff or otherwise) on account of any Loan, any Reimbursement Obligation or any other Obligation (other than pursuant to the terms ofSections
4.3,4.4and4.5) in excess of itspro
ratashare of payments then or therewith obtained by all Lenders, such Lender shall purchase from the other Lenders such participations as shall be necessary to cause such
purchasing Lender to share the excess payment or other recovery ratably with each of them;provided, however, that if all or any portion of the excess
payment or other recovery is thereafter recovered from such purchasing Lender, the purchase shall be
rescinded and each Lender which has sold a participation to the purchasing Lender shall repay to the purchasing Lender the purchase price to the ratable extent of such recovery together with an amount
equal to such selling Lender's ratable share (according to the proportion of (a) the amount of such selling Lender's required repayment to the purchasing Lender (b) the total amount so
recovered from the purchasing Lender) of any interest or other amount paid or payable by the purchasing Lender in respect of the total amount so recovered. The Borrower agrees that any Lender so
purchasing a participation from another Lender pursuant to this Section may, to the fullest extent permitted by law, exercise all its rights of payment (including pursuant to Section 4.9) with
respect to such participation as fully as if such Lender were the direct creditor of the Borrower in the amount of such
participation. If under any applicable bankruptcy, insolvency or other similar law, any Lender receives a secured claim in lieu of a setoff to which this Section applies, such Lender shall, to the
extent practicable, exercise its rights in respect of such secured claim in a manner consistent with the rights of the Lenders entitled under this Section to share in the benefits of any recovery on
such secured claim.

SECTION
4.9Setoff.Upon the occurrence of an Event of Default, each Lender shall be entitled to exercise (for
the benefit of all Lenders pursuant toSection 4.8) any right of offset or bankers' lien against each and every account and other property or
interest therein that the Borrower or any Obligor may now or hereafter have with, or which is now or hereafter in the possession of, such Lender, to the extent of the full amount of the Obligations.
To secure the Obligations, the Borrower hereby grants to
each Lender a continuing security interest in any and all balances, credits, deposits, accounts or moneys of the Borrower then or thereafter maintained with such Lender; provided,however, that any exercise of such security interest shall be subject to the provisions of Section 4.8. Each Lender agrees promptly to notify the Borrower and the
Canadian Administrative Agent after any such setoff and application made
by such Lender;provided,however, that the failure to give such notice shall not affect the validity of
such setoff and application. The rights of each Lender under this Section are in addition to other rights and remedies (including other rights of setoff under applicable law or otherwise) which such
Lender may have.

SECTION
4.10.Currency Conversion and Currency Indemnity.

(a)  Each
Obligor shall make payment relative to any Obligation in the currency (the "Agreed Currency") in which the
Obligation was incurred. If any payment is received on account of any

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Obligation in any currency (the "Other Currency") other than the Agreed Currency (whether voluntarily, pursuant to any conversion of a Loan or pursuant
to an order or judgment or the enforcement thereof or the realization of any security or the liquidation of such Obligor or otherwise howsoever), such payment shall constitute a discharge of the
liability of an Obligor hereunder and under the other Loan Documents in respect of such Obligation only to the extent of the amount of the Agreed Currency which the Canadian Administrative Agent and
Lenders are able to purchase with the amount of the Other Currency received by it on the Business Day next following such receipt in accordance with its normal procedures and after deducting any
premium and costs of exchange.

(b)  If
for the purpose of obtaining or enforcing judgment in any court in any jurisdiction, it becomes necessary to convert into a particular currency (the
"Judgment Currency") any amount due in the Agreed Currency then the conversion shall be made on the basis of the rate of exchange prevailing on the next
Business Day following the date such judgment is given and in any event each Obligor shall be obligated to pay the Canadian Administrative Agent and Lenders any deficiency in accordance with
Section 4.10(c). For the foregoing purposes, "rate of exchange" means the Noon Rate, after deducting any premium and costs of exchange.

(c)  If
the Canadian Administrative Agent or any Lender receives any payment or payments on account of the liability of an Obligor hereunder pursuant to any judgment or order
in any Other Currency, and the amount of the Agreed Currency which the relevant Canadian Administrative Agent or Lender is able to purchase on the Business Day next following such receipt with the
proceeds of such payment or payments in accordance with its normal procedures and after deducting any premiums and costs of exchange is less than the amount of the Agreed Currency due in respect of
such Obligations immediately prior to such judgment or order, then Borrower on demand shall indemnify and save such Canadian Administrative Agent and Lenders harmless from and against any loss, cost
or expense arising out of or in connection with such deficiency. The agreement of indemnity provided for in thisSection 4.10(c)shall constitute
an obligation separate and independent from all other obligations contained in this Agreement, shall give rise to a separate and independent cause of action, shall apply irrespective of any indulgence
granted by the Canadian Administrative Agent and the Lenders or any
of them from time to time, and shall continue in full force and effect notwithstanding any judgment or order for a liquidated sum in respect of an amount due hereunder or under any judgment or order.

ARTICLE V
CONDITIONS TO EFFECTIVENESS

SECTION
5.1Conditions to Effectiveness and Initial Borrowing.This Agreement shall be effective upon and the
obligations of the Lenders to continue the Borrowings and to continue the Letters of Credit hereunder shall be subject to the prior or concurrent satisfaction of each of the conditions precedent set
forth in thisSection 5.1. All certificates, agreements, opinions and other documents delivered shall be in form and substance satisfactory to
the Canadian Administrative Agent.

SECTION
5.1.1Resolutions, etc.The Canadian Administrative Agent shall have received from each Obligor a
certificate, dated the Effective Date, of its secretary, assistant secretary, manager or general partner as applicable as to (a) resolutions of its Board of Directors, Managers, or their
equivalent then in full force and effect authorizing the execution, delivery and performance of this Agreement, the Notes and each other Loan Document to be executed by it, (b) to the extent
not previously delivered, the articles or certificate of incorporation or organization, the bylaws, operating agreements, or partnership agreement of such Obligor, and (c) the incumbency and
signatures of those of its officers authorized to act with respect to this Agreement, the Notes and each other Loan Document executed by it, upon which certificate each Lender may conclusively rely
until it shall have received a further certificate of the secretary, manager or general partner as applicable of such Obligor canceling or amending such prior certificate. The Canadian Administrative
Agent shall have received

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from each Obligor certificates of good standing provided by the appropriate governmental officer in its jurisdiction of incorporation.

SECTION
5.1.2Delivery of this Agreement; "Effective Date" under U.S. Credit Agreement and MarkWest OLLC Credit
Agreement.The Canadian Administrative Agent shall have received (a) this Agreement and the Notes issued pursuant hereto, duly executed by each party
thereto, and in each case in form and substance satisfactory to the Canadian Administrative Agent, and (b) evidence satisfactory to it that the "Effective Date" under each of the U.S. Credit
Agreement and the MarkWest OLLC Credit Agreement shall occur on the Effective Date hereunder.

SECTION
5.1.3Guaranty Agreements.MarkWest Michigan, MarkWest Resources and Matrex, as Guarantors under the
Second Amended and Restated Guaranty Agreements dated as of the date of the Existing Credit Agreement, and the Parent and Midstream Services, as Guarantors under the Guaranty Agreement dated as of the
date of the Existing Credit Agreement, each shall have ratified their obligations under such Guaranties by executing this Agreement.

SECTION
5.1.4Collateral Documents.The Canadian Administrative Agent shall have received executed counterparts
of (a) the Collateral Documents described onSchedule 5.1.4, together with the other related documents therein described, and
(b) to the extent not previously delivered to Bank of America, N.A., as Administrative Agent, certificates evidencing all of the issued and outstanding shares of capital stock, partnership
interests, or membership interests pledged pursuant thereto, which certificates shall in each case be accompanied by undated stock powers duly executed in blank.

SECTION
5.1.5Closing Certificate.The Canadian Administrative Agent shall have received a certificate signed by
an Authorized Officer of the Borrower certifying (a) that the conditions specified inArticle Vhave been satisfied, (b) no Default
or Event of Default exists hereunder or under the Existing Credit Agreement, and (c) since December 31, 2001 there has occurred no event or circumstance which could reasonably be
expected to have a Material Adverse Effect, (d) except as set forth onSchedule 1.1(a)to the U.S. Credit Agreement, no litigation or
action exists or is pending or threatened which could reasonably be expected to have a Material Adverse Effect and (e) the representations and warranties set forth in Article VIand in each of
the other Loan Documents are true and correct in all material respects.

SECTION
5.1.6Opinions of Counsel.The Canadian Administrative Agent shall have received the following, each
dated the Effective Date and addressed to the Canadian Administrative Agent and all Lenders: (a) legal opinions from Davis, Graham & Stubbs LLP and from Barry Spector, counsel to the
Borrower and its Subsidiaries, substantially in the form ofExhibit E-1and Exhibit E-3hereto and (b) a legal opinion from Fraser Milner
Casgrain LLP, Canadian Counsel to the Borrower and its
Subsidiaries, substantially in the form ofExhibit E-2hereto.

SECTION
5.1.7Closing Fees, Expenses, etc.All fees and expenses to be paid on or before the Effective Date
shall have been paid, including attorneys' fees and expenses to the extent invoiced prior to the Effective Date.

SECTION
5.1.8Evidence of Insurance.The Canadian Administrative Agent shall have received certificates of
insurance satisfactory to it evidencing the existence of all insurance required to be maintained by the Borrower by this Agreement and the other Loan Documents, which insurance shall list Canadian
Administrative Agent as additional insured and a loss payee and be satisfactory to the Canadian Administrative Agent.

SECTION
5.1.9[Intentionally Blank]

SECTION
5.1.10Hedging Policy.The Canadian Administrative Agent shall have received a copy of the Hedging
Policy.

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SECTION 5.1.11Other.The Canadian Administrative Agent shall have received such other assurances,
certificates,
documents, consents or opinions as the Canadian Administrative Agent or the Required Lenders may require.

SECTION
5.2All Borrowings.The obligation of each Lender to fund any Loan on the occasion of any Borrowing and
to issue any Letter of Credit shall be subject to the satisfaction of each of the conditions precedent set forth in thisSection 5.3.

SECTION
5.2.1Compliance with Warranties, No Default, etc.    Both before and after giving effect to any Borrowing
or Letter of Credit (but, if any Default of the nature referred to inSection 8.1.5shall have occurred with respect to any other Indebtedness,
without giving effect to the application, directly or indirectly, of the proceeds thereof) the following statements shall be true and correct in all material respects (a) the representations
and warranties set forth inArticle VIand in each Loan Document shall be true and correct with the same effect as if then made (unless stated to
relate solely to an earlier date, in which case such representations and warranties shall be true and correct as of such earlier date); (b) except as disclosed by the Borrower to the Canadian
Administrative Agent and the Lenders pursuant toSection 6.7, (i) no labor controversy, litigation, arbitration or governmental
investigation or proceeding shall be pending or, to the knowledge of the Borrower, threatened against the Parent, Borrower or any of their Subsidiaries which could reasonably be expected to have a
Material Adverse Effect or which purports to affect the legality, validity or enforceability of this Agreement, the Notes, or any other Loan Document; and (ii) no development shall have
occurred in any labor controversy, litigation, arbitration, environmental or governmental investigation or proceeding disclosed pursuant to Section 6.7which could reasonably be expected to have a
Material Adverse Effect; and (c) no Default shall have then occurred and be
continuing, and neither the Parent, Borrower, any other Obligor, nor any of their Subsidiaries are in violation of any law or governmental regulation or court order or decree, which would have a
Material Adverse Effect.

SECTION
5.2.2Borrowing Request.(a) The Canadian Administrative Agent shall have received a Borrowing
Request signed by both the Borrower and the Parent for such Borrowing or Issuance Request for such Letter of Credit, as the case may be. Each of the delivery of a Borrowing Request or Issuance Request
for such Letter of Credit, as the case may be, and the acceptance by the Borrower of the proceeds of such Borrowing or such Letter of Credit shall constitute a representation and warranty by both the
Borrower and the Parent that on the date of such Borrowing (both immediately before and after giving effect to such Borrowing and the application of the proceeds thereof) the statements made in Section 5.3.1are true and correct.

(b)  In
addition, if Borrower is unable to make the representations and warranties set forth in paragraph 5 of the form of Borrowing Request attached hereto as Exhibit B, then Borrower shall deliver
to the Canadian Administrative Agent, not less than ten (10) days prior to the date of requested
Borrowing or Issuance Request, a certificate (a "Regulation U Compliance Certificate") in form and substance satisfactory to the Canadian
Administrative Agent setting forth calculations demonstrating compliance with Regulation U and, if required by the Canadian Administrative Agent, an opinion of counsel (a
"Regulation U Opinion") in form and substance satisfactory to the Canadian Administrative Agent stating that the Lenders and the Borrowers are,
and after the requested Borrowing or Issuance will be, in compliance with Regulation U.

SECTION
5.2.3Satisfactory Legal Form.All documents executed or submitted pursuant hereto by or on behalf of
the Borrower or any of its Subsidiaries or any other Obligors shall be satisfactory in form and substance to the Canadian Administrative Agent and its counsel (which satisfaction is acknowledged with
respect to any documents conforming to the respective exhibit attached hereto); and the Canadian Administrative Agent and its counsel shall have received all information, approvals, opinions,
documents or instruments as the Canadian Administrative Agent or its counsel may reasonably request.

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ARTICLE VI
REPRESENTATIONS AND WARRANTIES

In order to induce the Lenders and the Canadian Administrative Agent to enter into this Agreement and to make Loans hereunder, the Borrower represents and
warrants unto the Canadian Administrative Agent and each Lender as set forth in thisArticle VI, except as otherwise indicated on the Disclosure
Schedule:

SECTION
6.1Organization, etc.The Borrower and each of its Subsidiaries is a corporation or limited liability
company validly incorporated or organized and existing and in good standing under the laws of the province of its incorporation or formation, is duly qualified to do business and is in good standing
as a foreign corporation or limited liability company in each jurisdiction where the nature of its business requires such qualification, and has full power and authority and holds all requisite
governmental licenses, permits and other approvals to enter into and perform its Obligations under this Agreement, the Notes and each other Loan Document to which it is a party and to own and hold
under lease its property and to conduct its business substantially in accordance with the first recital.

SECTION
6.2Due Authorization, Non-Contravention, etc.The execution, delivery and performance by
the Borrower of this Agreement, the Notes and each other Loan Document executed or to be executed by it, and the execution, delivery and performance by each other Obligor of each Loan Document
executed or to be executed by it, are within the Borrower's and each such Obligor's corporate powers, have been duly authorized by all necessary corporate action, and do not (a) contravene the
Borrower's or any such Obligor's Organic Documents; (b) contravene any contractual restriction, law or
governmental regulation or court decree or order binding on or affecting the Borrower or any such Obligor; or (c) result in, or require the creation or imposition of, any Lien on any of any
Obligor's properties.

SECTION
6.3Government Approval, Regulation, etc.No authorization or approval or other action by, and no notice
to or filing with, any governmental authority or regulatory body or other Person is required for the due execution, delivery or performance by the Borrower of this Agreement, the Notes or any other
Loan Document to which it is a party, except for the filings of mortgages and lien notices in connection with the granting of security interests pursuant to the Collateral Documents. The Borrower and
its Subsidiaries possess all authorizations, approvals, permits and licenses necessary to operate their respective businesses as currently operated and as anticipated to be operated. Neither the
Borrower nor any of its Subsidiaries is an "investment company" within the meaning of the Investment Company Act of 1940, as amended, or a "holding company," or a "subsidiary company" of a "holding
company," or an "affiliate" of a "holding company" or of a "subsidiary company" of a "holding company," within the meaning of the Public Utility Holding Company Act of 1935, as amended.

SECTION
6.4Validity, etc.This Agreement constitutes, and the Notes and each other Loan Document executed by
the Borrower will, on the due execution and delivery thereof, constitute, the legal, valid and binding obligations of the Borrower enforceable in accordance with their respective terms; and each Loan
Document executed pursuant hereto by each other Obligor will, on the due execution and delivery thereof by such Obligor, be the legal, valid and binding obligation of such Obligor enforceable in
accordance with its terms.

SECTION
6.5Financial Information.The consolidated balance sheet of the Parent and its Subsidiaries as at
December 31, 2001, and the related consolidated statements of earnings and cash flow of the Parent and its Subsidiaries, copies of which have been furnished to the Canadian Administrative Agent
and each Lender, have been prepared in accordance with GAAP consistently applied, and present fairly the consolidated financial condition of the entities covered thereby as at the dates thereof and
the results of their operations for the periods then ended. The Parent and each of the MarkWest Inc. Subsidiaries are in compliance with all of their existing financial obligations.

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SECTION
6.6No Material Adverse Change.Since December 31, 2001, there has not been any Material Adverse
Effect.

SECTION
6.7Litigation, Labor Controversies, etc.As of the Effective Date, except as disclosed in Schedule 1.1(a), there is no pending or, to the knowledge of the Borrower, threatened litigation, action, proceeding, or labor controversy
affecting the Borrower or any of its Subsidiaries, or any of their respective properties, businesses, assets or revenues, which could reasonably be expected to have a Material Adverse Effect or which
purports to affect the legality, validity or enforceability of this Agreement, the Notes or any other Loan Document.

SECTION
6.8Subsidiaries.The Borrower has no Subsidiaries, except those Subsidiaries (a) which are
identified inItem 6.8("Existing Subsidiaries") of the Disclosure Schedule; or (b) which are permitted to have been acquired in accordance with Section 7.2.5or7.2.8. Each Subsidiary has executed a Guaranty.

SECTION
6.9Ownership of Properties.The Borrower and each of its Subsidiaries owns good and defensible title to
all of its properties and assets, real and personal, tangible and intangible, of any nature whatsoever (including patents, trademarks, trade names, service marks and copyrights), free and clear of all
Liens, charges or claims (including infringement claims with respect to patents, trademarks, copyrights and the like) except as permitted pursuant to Section 7.2.3.

SECTION
6.10Taxes.The Borrower and each of its Subsidiaries has filed all tax returns and reports required by
law to have been filed by it and has paid all taxes and governmental charges thereby shown to be owing, except any such taxes or charges which are being diligently contested in good faith by
appropriate proceedings and for which adequate reserves in accordance with GAAP shall have been set aside on its books.

SECTION
6.11[Intentionally Blank]

SECTION
6.12Compliance with Law.Neither the Borrower nor any of its Subsidiaries (a) is in violation of
any law, statute, ordinance, decree, requirement, order, judgment, rule, regulation (or any interpretation of the foregoing) of, or the terms of any license or permit issued by, any governmental
authority; or (b) has failed to obtain any license, permit, franchise or other governmental authorization necessary to ownership of any of their respective properties or the conduct of their
respective business; which violation or failure could reasonably be expected to have a Material Adverse Effect.

SECTION
6.13Claims and Liabilities.Neither the Borrower nor any of its Subsidiaries has accrued any
liabilities under gas purchase contracts for gas not taken, but for which it is liable to pay if not made up and which, if not paid, would have a Material Adverse Effect. No claims exist against the
Borrower or its Subsidiaries for gas imbalances which claims if adversely determined would have a Material Adverse Effect. No purchaser of product supplied by the Borrower or any of its Subsidiaries
has any claim against the Borrower or any of its Subsidiaries for product paid for, but for which delivery was not taken as and when paid for, which claim if adversely determined would have a Material
Adverse Effect.

SECTION
6.14No Prohibition on Perfection of Collateral Documents.None of the terms or provisions of any
indenture, mortgage, agreement or other instrument to which the Borrower or any of its Subsidiaries is a party or by which the Borrower or any of its Subsidiaries or the property of the Borrower or
any of its Subsidiaries is bound (other than documentation governing Permitted Liens described inclauses (a), (c),(q)and(r)) prohibit the filing or recordation of
any of the Loan Documents or any other action which is necessary or appropriate in connection with the perfection or
maintenance of the Liens on material assets evidenced and created by any of the Loan Documents. Notwithstanding the foregoing, documents governing a Capitalized Lease Liability or a purchase money
Lien permitted bySection 7.2.3(q)and(r)may prohibit other Liens on the asset encumbered by
such Lien.

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SECTION
6.15Solvency.The Borrower is, and the Borrower and its Subsidiaries on a consolidated basis are,
solvent (as such term is used in applicable bankruptcy, liquidation, receivership, insolvency and similar laws).

SECTION
6.16Environmental Warranties.In the ordinary course of its business, the Borrower conducts an ongoing
review of the effect of Environmental Laws on the business, operations and properties of the Borrower and its Subsidiaries, in the course of which it identifies and evaluates associated liabilities
and costs (including any capital or operating expenditures required for clean-up or closure of properties presently owned or operated, any capital or operating expenditures required to
achieve or maintain compliance with environmental protection standards imposed by law or as a condition of any license, permit or contract, any related constraints on operating activities, including
any periodic or permanent shutdown of any facility or reduction in the level of or change in the nature of operations conducted thereat and any actual or potential liabilities to third parties,
including employees, and any related costs and expenses). On the basis of this review, the Borrower has reasonably concluded that, except as set forth in Schedule 1.1(a)hereto, to the best of its
knowledge after due inquiry:



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SECTION
6.17Regulations T, U and X.The Borrower is not engaged and will not engage, principally or as one of
its important activities, in the business of purchasing or carrying margin stock, and no proceeds of any Loans will be used for a purpose which violates, or would be inconsistent with, F.R.S. Board
Regulation T, U or X. Terms for which meanings are provided in F.R.S. Board Regulation T, U or X or any regulations substituted therefor, as from time to time in effect, are used in this
Section with such meanings. As of the Effective Date, the Borrower does not own any Margin Stock.

SECTION
6.18Accuracy of Information.All material factual information heretofore or contemporaneously furnished
by or on behalf of the Borrower in writing to the Canadian Administrative Agent or any Lender for purposes of or in connection with this Agreement or any transaction contemplated hereby is, and all
other such factual information hereafter furnished by or on behalf of the Borrower to the Canadian Administrative Agent or any Lender will be, true and accurate in all material respects on the date as
of which such information is dated or certified, and except as amended or superseded by any such information subsequently provided prior to the date of execution and delivery of this Agreement, as of
the date of execution and delivery of this Agreement by the Canadian Administrative Agent and such Lender, and such information is not, or shall not be, as the case may be, incomplete by omitting to
state any material fact necessary to make such information not misleading. All estimates and projections delivered to the Canadian Administrative Agent or any Lender were based upon information that
was available at the time such estimates or projections were made and believed to be correct and upon assumptions believed to be reasonable; however the
Borrower does not warrant that such estimates and projections will ultimately prove to have been accurate.

SECTION
6.19Default.No Default or Event of Default has occurred and is continuing.

SECTION
6.20[Intentionally Blank]

SECTION
6.21Oil and Gas Reserves.The Borrower and each Subsidiary is and will hereafter be, in all material
respects, the owner of the Hydrocarbon Interests that it purports to own from time to time in and under its Oil and Gas Properties, together with the right to produce the same. The Hydrocarbon
Interests are not subject to any Lien other than Permitted Liens. All Oil and Gas have been and will hereafter be produced, sold and delivered in accordance in all material respects with all
applicable laws and regulations; each of the Borrower and its Subsidiaries has complied in all material respects and will hereafter use commercially reasonable efforts to comply with all material
terms of each oil, gas and mineral lease comprising its Hydrocarbon Interests; and all such oil, gas and mineral leases have been and will hereafter be maintained in full force and effect; provided,however, that nothing in this Section 6.21shall prevent the Borrower or its Subsidiaries from (a) selling or otherwise disposing of assets as
permitted by Section 7.2.9or (b) abandoning any well or forfeiting, surrendering, releasing or defaulting under any lease in the ordinary course of
business and which, in the opinion of the Borrower or its Subsidiaries, is in its best interest,provided, thatthe Borrower and its Subsidiaries is and
will hereafter be in compliance with all obligations hereunder. To the best of the knowledge of the
Borrower all agreements pursuant to which Borrower and its Subsidiaries own their Hydrocarbon Interests are and will hereafter be enforceable in all material respects in accordance with their terms
except as such may be modified by applicable bankruptcy law or an order of a court in equity.

SECTION
6.22Reserve Report; Title Opinion.(a) The Borrower has heretofore delivered to the Canadian
Administrative Agent a true and complete copy of the Reserve Report effective January 1, 2002 covering certain of the Borrower's Oil and Gas Properties located in Canada relating to an
evaluation of the Oil and Gas attributable to certain of the Oil and Gas Properties described therein. To the best knowledge of the Borrower, (a) the assumptions stated or used in the
preparation of such Reserve Report are reasonable, (b) all information furnished by the Borrower to the Independent Engineer for use in the preparation of such Reserve Report was accurate in
all material respects and

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(c) there has been no material adverse change in the amount of the estimated Oil and Gas shown in such Reserve Report since the date thereof, except for changes which have occurred as a result
of production in the ordinary course of business.

(b)  The
Borrower has heretofore delivered a title opinion to the Administrative Agent describing in all material respects the status of title to at least 75% of the value of
the Borrower's and its Subsidiary's Oil and Gas Properties included in the Reserve Report effective January 1, 2002.

ARTICLE VII
COVENANTS

SECTION
7.1Affirmative Covenants.Each of the Borrower and Parent (by its execution of a Guaranty) agrees with
the Canadian Administrative Agent and each Lender that, until all Revolving Loan Commitments have terminated and all Obligations have been paid and performed in full, the Borrower will perform the
obligations set forth in thisSection 7.1.

SECTION
7.1.1Financial Information, Reports, Notices, etc.The Borrower or the Parent will furnish, or will
cause to be furnished, to the Canadian Administrative Agent sufficient copies of the following financial statements, reports, notices and information to provide one to each Lender:



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SECTION
7.1.2Compliance with Laws, etc.The Borrower will, and will cause each of its Subsidiaries to, comply
with all applicable laws, rules, regulations and orders (including Environmental Laws), such compliance to include, without limitation, (a) the maintenance and preservation of its corporate,
partnership or limited liability company existence and qualification as a foreign corporation, partnership or limited liability company; and (b) the payment, before the same become delinquent,
of all taxes, assessments and governmental charges imposed upon it or upon its property except to the extent being diligently contested in good faith by appropriate proceedings and for which adequate
reserves in accordance with GAAP shall have been set aside on its books, except where the failure to so comply with the terms of this Section 7.1.2 shall not reasonably be expected to have a
Material Adverse Effect.

SECTION
7.1.3Maintenance of Properties.The Borrower will, and will cause each of its Subsidiaries to,
maintain, preserve, protect and keep its properties in good repair, working order and condition in all material respects, and make necessary and proper repairs, renewals and replacements so that its
business carried on in connection therewith may be properly conducted at all times unless the Borrower determines in good faith that the continued maintenance of any of its properties is no longer
economical..

SECTION
7.1.4Use of Proceeds.The proceeds of the Loans shall be used to continue the existing indebtedness of
the Borrower under the Existing Credit Agreement and for general corporate and working capital purposes of the Borrower and its Subsidiaries.

SECTION
7.1.5Insurance.(a) The Borrower will, and will cause each of its Subsidiaries to, maintain or
cause to be maintained with responsible insurance companies insurance with respect to its properties and business (including business interruption insurance) against such casualties and contingencies
and of such types and in such amounts as is customary in the case of similar businesses and which is satisfactory to the Canadian Administrative Agent and the Required Lenders and will
(i) furnish to the Canadian Administrative Agent on each anniversary of the Effective Date a certificate or certificates of insurance from Borrower's insurance companies evidencing the
existence of all

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insurance required to be maintained by the Borrower by this Agreement and the other Loan Documents and that Canadian Administrative Agent is listed as additional insured and sole loss payee and
(ii) upon request of the Canadian Administrative Agent, furnish to each Lender at reasonable intervals a certificate of an Authorized Officer of the Borrower setting forth the nature and extent
of all insurance maintained by the Borrower and its Subsidiaries in accordance with this Section.

(b)  Except
as the Canadian Administrative Agent may otherwise consent to in writing, Borrower will, and will cause each of its Subsidiaries to, forthwith upon receipt,
transmit and deliver to the Canadian Administrative Agent, in the form received, all cash, checks, drafts, chattel paper and other instruments or writings for the payment of money in excess of
$250,000 (properly endorsed, where required, so that such items may be collected by the Canadian Administrative Agent) that may be received by the Borrower at any time in full or partial payment of
amounts due under any such insurance policy. Except as the Canadian Administrative Agent may otherwise consent in writing, any such items which may be received by the Borrower will not be commingled
with any other of its funds or property, but will be held separate and apart from its own funds or property and upon express trust for the Canadian
Administrative Agent until delivery is made to the Canadian Administrative Agent. Borrower will comply with the terms and conditions of any consent given by the Canadian Administrative Agent pursuant
to the provisions of this paragraph.

(c)  All
items or amounts which are delivered by the Borrower or by any insurance company to the Canadian Administrative Agent on account of partial or full payment of
amounts due under any insurance policy with respect to the Borrower or any of its Subsidiaries shall be deposited to the credit of a deposit account (herein called the
"Insurance Deposit Account") of the Borrower with the Canadian Administrative Agent, as security for payment of the Obligations. Borrower shall have no
right to withdraw any funds deposited in the Insurance Deposit Account. Subject toSection 3.1(c), the Canadian Administrative Agent will apply
all or any of the then balance in the Insurance Deposit Account towards payment of the Obligations, in such order of application as the Canadian Administrative Agent may determine. The Canadian
Administrative Agent may, from time to time, in its reasonable discretion and with the consent of the Required Lenders, release all or any of such balance representing collected funds to the Borrower.
The Canadian Administrative Agent is authorized to endorse, in the name of the Borrower, any item, howsoever received by the Canadian Administrative Agent, representing any payment under any such
insurance policy.

(d)  The
Borrower hereby grants to the Administrative Agent, for the benefit of the Lenders, a lien on and security interest in and to the Insurance Deposit Account and all
monies, cash, checks, drafts, certificates of deposit, instruments, investment property, and other items ever received by Administrative Agent for deposit therein and held therein, as security for the
Obligations. The rights granted by thisSection 7.1.5shall be in addition to the rights of the Administrative Agent under any statutory banker's
Lien or the common law right of setoff.

SECTION
7.1.6Books and Records.The Borrower will, and will cause each of its Subsidiaries to, keep books and
records which accurately reflect all of its business affairs and transactions and permit the Canadian Administrative Agent and each Lender or any of their respective representatives, at reasonable
times and intervals, to visit all of its offices and properties, to discuss its financial matters with its officers and independent public accountant (and the Borrower hereby authorizes such
independent public accountant to discuss the Borrower's financial matters with each Lender or its representatives with a representative of the Borrower present) and to examine (and, at the expense of
the Borrower, photocopy extracts from) any of its books or other corporate records. The Borrower shall pay any fees of such independent public accountant incurred in connection with the Canadian
Administrative Agent's or any Lender's exercise of its rights pursuant to this Section.

SECTION
7.1.7Environmental Covenant.The Borrower will, and will cause each of its Subsidiaries to,
(a) use and operate all of its facilities and properties in compliance with all

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Environmental Laws, keep all necessary permits, approvals, certificates, licenses and other authorizations relating to environmental matters in effect and remain in compliance therewith, and handle
all Hazardous Materials in compliance with all applicable Environmental Laws, except where the failure to so comply shall not reasonably be expected to have a Material Adverse Effect; and
(b) provide such information and certifications which the Canadian Administrative Agent may
reasonably request from time to time to evidence compliance with thisSection 7.1.7;provided, thatneither the Canadian Administrative Agent nor any Lender shall have any obligation to make any inquiries pursuant to this Section 7.1.7.

SECTION
7.1.8Further Assurances; Additional Collateral; Recording of Liens.(a) The Borrower shall, the
Parent shall, and the Parent shall cause each MarkWest Inc. Operating Subsidiary to, from time to time, become an Obligor with respect to, and jointly and severally liable with all other
Obligors for, all the Obligations under this Agreement and the Notes and the other Loan Documents by promptly executing and delivering to the Lenders a Guaranty substantially in the form of Exhibit G-1orG-2hereto, with appropriate insertions, and by causing
each MarkWest Inc. Operating Subsidiary's, as the case may be, capital stock, partnership, joint venture or membership interest to be pledged pursuant to a pledge agreement in form satisfactory
to the Canadian Administrative Agent.

(b)  The
Borrower shall, the Parent shall and the Parent shall cause each MarkWest Inc. Operating Subsidiary to, take such actions and to execute and deliver such
documents and instruments as the Canadian Administrative Agent shall require to ensure that the Canadian Administrative Agent or the Administrative Agent on behalf of the Lenders shall, at all times,
have received currently effective duly executed Security Agreements and other Loan Documents encumbering substantially all of the assets of the Borrower, the Parent and each of the
MarkWest Inc. Operating Subsidiaries, including (i) 100% of the stock or other equity interest in each MarkWest Inc. Operating Subsidiary organized under the laws of the United
States, (ii) 100% of the stock or other equity interests in each Subsidiary of Borrower, (iii) 75% of the total value of all of the Parent's and the MarkWest Inc. Operating
Subsidiaries' Oil and Gas Properties evaluated in the most recent Reserve Report, and (iv) all of the Parent's and the MarkWest Inc. Operating Subsidiaries' other material assets and
properties, both tangible and intangible, both personal and real, other than (A) assets encumbered by Liens permitted bySection 7.2.3(q), (r)and(s)hereunder andSection 7.2.3(p), (q)and(r)of
the U.S. Credit Agreement and (B) partnership interests in the MLP.

(c)  (i)
In connection with the actions required pursuant to the foregoingsubsections (a)and (b), the Parent shall, and shall cause the MarkWest Inc.
Operating Subsidiaries to execute and deliver such stock certificates, blank stock
powers, evidence of corporate authorization, opinions of counsel, current valuations, evidence of title, title opinions, title insurance and other documents, and shall use commercially reasonable
efforts to obtain landlord and mortgagee waivers and third party consents, as shall be requested by the Canadian Administrative Agent, in each case in form and substance satisfactory to the Canadian
Administrative Agent.



(d)  The
liens required by thisSection 7.1.8shall be first priority perfected liens in favor of the Canadian
Administrative Agent, subject to no other liens except Permitted Liens. If the Canadian Administrative Agent shall determine that, as of any date, the Borrower shall have failed to comply

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with thisSection 7.1.8, the Canadian Administrative Agent may (and at the direction of the Required Lenders, shall) notify the Borrower in
writing of such failure and, within 30 days from and after receipt of such written notice by the Borrower, the Borrower shall, or the Parent shall cause any of its Subsidiaries to, execute and
deliver to the Canadian Administrative Agent supplemental or additional Loan Documents, in form and substance satisfactory to the Canadian Administrative Agent and its counsel, securing payment of the
Notes and the other Obligations and covering additional assets and properties not then encumbered by any Loan Documents (together with such current valuations, engineering reports, appraisals, and
title opinions or insurance applicable to the additional assets and properties collaterally assigned, as may be requested by the Canadian Administrative Agent, each of which shall be in form and
substance satisfactory to the Canadian Administrative Agent) such that the Canadian Administrative Agent shall have received currently effective duly executed and perfected Collateral Documents
encumbering substantially all of the material assets and properties of the Parent and the MarkWest Inc. Operating Subsidiaries as required by Section 7.1.8(b).

(e)  Without
limiting any of the foregoing provisions of thisSection 7.1.8, at any time the Canadian Administrative
Agent may, or upon the direction of the Required Lenders shall, register such security notices, caveats, liens, and charges and file such Mortgages and other instruments as the Canadian Administrative
Agent may deem necessary or appropriate in connection with the Collateral, including Oil and Gas Properties.

SECTION
7.1.9Compliance with Hedging Policy; Hedging Agreements.(a) Borrower shall at all times comply
in all material respects with, and perform any and all obligations and actions set forth in, the terms and provisions of the Hedging Policy. No changes shall be made to the Hedging Policy except in
compliance withSection 7.2.1.

(b)  The
Parent shall maintain the commodity price protection agreements described inSchedule 7.1.9covering the
Parent's and the MarkWest Inc. Subsidiaries' Canadian Oil and Gas Properties during the period from the Effective Date and ending on December 31, 2004. The Parent shall maintain the
hedged position required by thisSection 7.1.9(b)during the period and in accordance with the terms specified herein.

SECTION
7.1.10Hedging Agreements.The Parent shall (a) as soon as available and in any event within
(i) 30 days after the end of each month (other than December), and (ii) within 45 days after the end of each December, deliver to the Canadian Administrative Agent a
summary of all existing Hedging Agreements entered into by Parent or any of the MarkWest Inc. Subsidiaries for its own account, including, without limitation, the amount of the Hedging
Obligation, the quantity of hedged volumes and the hedged price relating to each such Hedging Agreement, and the Counterparty for each such Hedging Agreement, and (b) at the request of the
Canadian Administrative Agent, provide the Canadian Administrative Agent with a copy of such Hedging Agreement, any related confirmations and/or any similar documentation for each such Hedging
Agreement.

SECTION
7.1.11Performance of Obligations.The Borrower shall (and shall cause its Subsidiaries to, comply in
all material respects with all of its (and their) obligations under all material contracts including, but not limited to, contracts relating to the properties of the Borrower or its Subsidiaries or by
which the Borrower (or such Subsidiaries, as applicable) are bound except to the extent such non-compliance could reasonably be expected to have a Material Adverse Effect.

SECTION
7.1.12Payment of Taxes and Claims.The Borrower will and will cause each of its Subsidiaries to file
all tax returns required to be filed in any jurisdiction and to pay and discharge all taxes shown to be due and payable on such returns and all other taxes, assessments, governmental charges, or
levies imposed on them or any of their properties, assets, income or franchises, to the extent such taxes and assessments have become due and payable and before they have become delinquent and all
claims for which sums have become due and payable that have or might become a Lien on properties or assets of the Borrower or any Subsidiary,provided, thatneither the Borrower nor

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any Subsidiary need pay any such tax or assessment or claims if (a) the amount, applicability or validity thereof is contested by the Borrower or such Subsidiary on a timely basis in good
faith and in appropriate proceedings, and the Parent or the Borrower or a Subsidiary has established adequate reserves therefor in accordance with GAAP on the books of the Parent, Borrower or such
Subsidiary or (b) the nonpayment of all such taxes and assessments in the aggregate could not reasonably be expected to have a Material Adverse Effect.

SECTION
7.2Negative Covenants.The Borrower agrees with the Canadian Administrative Agent and each Lender that,
until all Revolving Loan Commitments have terminated, all Obligations have been paid and performed in full, and no Letters of Credit remain outstanding, the Borrower will perform the obligations set
forth in thisSection 7.2.

SECTION
7.2.1Business Activities; Changes In Hedging Policy.    (a) The Borrower will not, and will not
permit any of its Subsidiaries to, engage in any business activity, except those described in thefirst recitaland such activities as may be incidental
or related thereto.

(b)  Prior
to making any material change after the date hereof in the Borrower's natural gas, natural gas liquids and crude oil marketing business or Hedging Policy
(including any net open position), the Borrower will give ten (10) Business Days advance notice to Canadian Administrative Agent and the Lenders.

SECTION
7.2.2Indebtedness.The Borrower will not, and will not permit any of its Subsidiaries to, create,
incur, assume or suffer to exist or otherwise become or be liable in respect of any Indebtedness, other than, without duplication, the following: (a) Indebtedness in respect of the Loans and
other Obligations; (b) [Intentionally Blank]; (c) unsecured Indebtedness incurred in the ordinary course of
business consisting of open accounts extended by suppliers and customers on normal trade terms in
connection with purchases or sales of goods and services not overdue by more than 60 days, but excluding Indebtedness incurred through the borrowing of money or Contingent Liabilities;
(d) (i) at any time that the U.S. Credit Agreement is not in effect, other Indebtedness of the Borrower and its Subsidiaries in an aggregate amount not to exceed Cdn. $4,227,390, and
(ii) at any time that the U.S. Credit Agreement is in effect, Indebtedness in an aggregate principal amount not greater than Cdn. $7,828,500; (e) Indebtedness owed by (i) a
Subsidiary to the Borrower, (ii) the Borrower or a Subsidiary to a Wholly-Owned Subsidiary, and (iii) the Borrower or one of its Subsidiaries to the Parent, provided thatin each such case
under thisclause (e), such Indebtedness is evidenced by a
promissory note which has been pledged to secure the Obligations and is in the possession of the Administrative Agent or the Canadian Administrative Agent, and such Indebtedness is subordinated to the
Obligations upon terms and conditions satisfactory to the Canadian Administrative Agent; and (f) Indebtedness resulting from any Hedging Obligations providedthat (i) such obligations are (or
were) entered into in the ordinary course of business for the purpose of directly mitigating risks
associated with the business of the Borrower or its Subsidiaries and not for purposes of speculation; and (ii) the agreements documenting such Hedging Obligations do not contain any provision
exonerating the non-defaulting party from its obligation to make payments on outstanding transactions to the defaulting party;provided, however,
notwithstanding the foregoing, (i) the Borrower will not, and will not permit any of its Subsidiaries to, create, incur, assume or
otherwise become or be liable in respect of any additional Indebtedness otherwise permitted byclause (d)if, after giving effect to the
incurrence thereof, any Default shall have occurred and be continuing and (ii) the Parent shall cause the MarkWest OLLC Credit Agreement and any and all refinancings thereof to be
Non-Recourse to the MLP's General Partner.

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SECTION 7.2.3Liens.The Borrower will not, and will not permit any of its Subsidiaries to, create, incur,
assume or suffer to exist any Lien upon any of its property, revenues or assets, whether now owned or hereafter acquired, except the following ("Permitted
Liens"):



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SECTION
7.2.4Financial Covenants.The Parent shall not permit:



Maximum Leverage Ratio

As of the Date of
each Fiscal Quarter Ending
as Set Forth Below3.75

3/31/023.50

6/30/023.25

9/30/023.00

12/31/02 and Fiscal Quarters ending thereafter




SECTION
7.2.5Investments.The Borrower will not, and will not permit any of its Subsidiaries to, make, incur,
assume or suffer to exist any Investment in any other Person, except: (a) Investments existing on the Effective Date and identified in Item 7.2.5(a) ("Existing
Investments") of the Disclosure Schedule; (b) Cash Equivalent Investments; (c) without duplication, Investments permitted as Indebtedness pursuant to Section 7.2.2; (d) in the ordinary course of business, Investments by the Borrower or any of its Subsidiaries in any Subsidiary by way of
contributions to capital, loans or advances, subject to Section 7.2.2in the case of loans or advances,provided, the Borrower and its Subsidiaries
shall
not make Investments in the Excluded MLP Entities if an MLP Credit Agreement Default has occurred and is continuing; (e) Investments incurred in order to consummate Acquisitions, provided, that no
Default of Event of Default exists or would occur as a result thereof, and such Acquisition shall have been approved or consented to
by the board of directors or similar governing entity of the Person being acquired; and (f) acquisition of not more than 5% of the outstanding equity securities of any Person (other than the
Borrower and the MLP);provided,however, that (A) any Investment which when made complies with
the requirements of the definition of the term "Cash Equivalent Investment" may continue to be held notwithstanding that such Investment if made
thereafter would not comply with such requirements; (B) no Investment otherwise permitted by clause (f) shall be permitted to be made if, immediately before or after giving effect
thereto, any Default shall have occurred and be continuing; and (C) any Investment otherwise permitted by clauses (d), (e), or (f) in an entity engaged in or to be engaged in the natural
gas, natural gas liquids or crude oil or other energy marketing business shall be structured in a manner acceptable to the Required Lenders.

SECTION
7.2.6Restricted Payments, etc.On and at all times after the Effective Date, the Borrower will not
permit any of its Subsidiaries to declare, pay or make any dividend or distribution (in cash, property or obligations) on any shares of any class of capital stock or other equity interests (now or
hereafter outstanding) of such Subsidiary or on any warrants, options or other rights with respect to any shares of any class of capital stock or other equity interests (now or hereafter outstanding)
of its Subsidiaries ("Restricted Payments") other than (a) dividends or distributions payable in its common

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stock or warrants to purchase its common stock or splitups or reclassifications of its stock into additional or other shares of its common stock; and (b) each Subsidiary of the Borrower may
make Restricted Payments to the Borrower and to Wholly-Owned Subsidiaries of the Borrower (and, in the case of a Restricted Payment by a non-wholly-owned Subsidiary of the Borrower, to the
Borrower and any Subsidiary of the Borrower and to each other owner of equity interests of such Subsidiary on a pro rata basis based on their relative ownership interests). The Borrower will not
permit any Subsidiary to make any deposit for any purchase, redemption, distribution or other payment that would be prohibited by this Section.

SECTION
7.2.7Rental Obligations.The Borrower will not, and will not permit any of its Subsidiaries to, enter
into at any time any arrangement ("Leases") (excluding oil and gas leases entered into in the ordinary course of business and leases which create
Capitalized Lease Liabilities permitted underSection 7.2.2(d)) which involves the leasing by the Borrower or any of its Subsidiaries from any
lessor of any real or personal property (or any interest therein), including, without limitation, pursuant to any sale-leaseback transaction, except arrangements which, together with all
Leases entered into by the Parent and all of the MarkWest Inc. Operating Subsidiaries (including the Borrower) which shall then be in effect will not require the payment of an aggregate amount
of rentals by the Borrower and the MarkWest Inc. Operating Subsidiaries during the full remaining term of such Leases in excess of (excluding escalations resulting from a rise in the consumer
price or similar index) U.S. $7,500,000 exclusive of expenses for maintenance, repair, insurance, taxes, and assessments, and similar charges;provided, however, that any calculation made for purposes of this Section shall exclude any amounts required to be expended for maintenance and repairs,
insurance, taxes, assessments, and other similar charges.

SECTION
7.2.8Consolidation, Merger, etc.The Borrower will not, and will not permit any of its Subsidiaries to
merge or consolidate with or into any Person except that, so long as no Default or Event of Default exists or would result therefrom:



SECTION
7.2.9Asset Dispositions, etc.(a) The Borrower will not, and will not permit any of its
Subsidiaries to, sell, transfer, lease, contribute or otherwise convey, or grant options, warrants or other rights with respect to, all or any substantial part of its assets (including capital stock
of Subsidiaries) to any Person.

(b)  The
Borrower will not, and will not permit any of its Subsidiaries to, sell, convey, contribute or transfer any asset (including, without limitation, any sale or
assignment with or without recourse of any receivable) except: (i) retirement of assets in the ordinary course of business; (ii) the sale of Oil and Gas production and sale of inventory
in the ordinary course of business, including in connection with hedge agreements or pursuant to long-term contracts; (iii) any conveyance or transfer by a Subsidiary of the
Borrower to the Borrower, or by the Borrower or a Subsidiary of the Borrower to a Wholly-Owned Subsidiary of Borrower; (iv) transfers by the Borrower to a Subsidiary permitted by

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Section 7.2.5; and (v) any other sale, conveyance, contribution or transfer of any asset or assets other than accounts receivable (the transfers permitted
pursuant to this clause (v) being referred to as a "Sale"),provided,any such Sales made since
the date of the most recent Canadian Borrowing Base redetermination exceeding, individually or in the aggregate, ten percent (10%) of the Canadian Borrowing Base then in effect, shall result in a
review of the Canadian Borrowing Base as provided in this Section. The Borrower shall give the Administrative Agent and the Global Lenders notice of any such proposed Sale not less than twenty
(20) Business Days prior to the anticipated closing date of the proposed Sale. The Administrative Agent shall, within ten (10) Business Days and utilizing the Reserve Report and
Midstream Report delivered in connection with the most recent redetermination of the Canadian Borrowing Base, and any other information deemed relevant by the Canadian Administrative Agent propose to
the Global Lenders the amount of the Canadian Borrowing Base to be in effect after such Sale. Thereafter, the Global Lenders shall have eight (8) Business Days to approve or object to such
proposed amount; and any failure to object shall be deemed to be an approval. In the event there
is no approval or deemed approval, the Administrative Agent shall poll the Global Lenders to ascertain the greatest amount of the Canadian Borrowing Base then acceptable to all of the Global Lenders
and such amount shall be the amount of the Canadian Borrowing Base. The Administrative Agent shall give the Borrower and the Global Lenders notice of the amount of the revised Canadian Borrowing Base,
and, if the U.S. Credit Agreement is effective, the Borrower may reallocate the sum of the U.S. Semi-Annual Borrowing Base and the revised Canadian Borrowing Base as provided in Section 2.1.3(a)(ii)of the U.S. Credit Agreement. If the U.S. Credit Agreement is not effective, references in this paragraph to Administrative
Agent shall mean Canadian Administrative Agent, Global Lenders shall mean Lenders, and Required Global Lenders shall mean Required Lenders. Notwithstanding the foregoing, the Borrower shall not, nor
shall the Borrower permit any of its Subsidiaries to, transfer any assets, other than the sale of Oil and Gas production and inventory and payment of trade payables in the ordinary course of business
pursuant toSection 7.2.9(b)(ii), to any Person pursuant to thisSection 7.2.9if a
Default shall have occurred and be continuing or would otherwise be existing after, or result from, any such transfer.

SECTION
7.2.10Subordinated Debt Documents.The Parent will not amend any Subordinated Debt Document unless
approved in writing by the Required Lenders (other than ministerial amendments and amendments to extend the time or times for payment). The Parent shall not make any payments of interest or any other
amounts in respect of the Subordinated Debt if a Default shall have occurred and be continuing or would result from such payment. The Parent will not prepay any principal, interest or other
indebtedness in respect of Subordinated Debt, or make any redemption or acquisition for value or defeasance, refinancing or exchange (other than for PIK Notes) thereof or therefor, or make any
payments in contravention of the Subordination Agreement. Any PIK Notes shall have the same terms as the related Subordinated Notes, except as otherwise approved by the Required Lenders, and shall be
considered Subordinated Notes for purposes of this Agreement and the Subordination Agreement.

SECTION
7.2.11Transactions with Affiliates.The Borrower will not, and will not permit any of its Subsidiaries
to, enter into, or cause, suffer or permit to exist any arrangement or contract with any of its other Affiliates unless such arrangement or contract is fair and equitable to the Borrower or such
Subsidiary and is an arrangement or contract of the kind which would be entered into by a prudent Person in the position of the Borrower or such Subsidiary with a Person which is not one of its
Affiliates.

SECTION
7.2.12Negative Pledges, Restrictive Agreements, etc.(a) The Borrower will not, and will not
permit any of its Subsidiaries to, enter into any agreement (excluding this Agreement, any other Loan Document and Loan Documents as defined in the U.S. Credit Agreement) prohibiting or restricting
the creation or assumption of any Lien upon its properties, revenues or assets, whether now owned or hereafter acquired, or the ability of the Borrower or any other Obligor to amend or

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otherwise modify this Agreement or any other Loan Document or the ability of the Borrower or any Subsidiary to make any payments, directly or indirectly, to the Borrower or to the Parent by way of
dividends, advances, repayments of loans or advances, reimbursements of management and other intercompany charges, expenses and accruals or other returns on investments, or any other agreement or
arrangement which restricts the ability of any such Subsidiary to make any payment, directly or indirectly, to the Borrower or the ability of the Borrower to make any payment, directly or indirectly,
to the Parent. Notwithstanding the foregoing, documents governing a Capitalized Lease Liability or a
purchase money Lien permitted bySection 7.2.3(q)and(r)may prohibit other Liens on the asset
encumbered by such Lien.

(b)  The
Borrower will not, and will not permit any of its Subsidiaries to, enter into any agreement governing Indebtedness if such agreement contains covenants or events of
default that are more restrictive than those contained in this Agreement;provided,however, that the
foregoing restriction shall not apply to the Loan Documents as defined in the U.S. Credit Agreement.

SECTION
7.2.13Limitation On Hedging Agreements.Neither the Borrower nor any of its Subsidiaries will enter
into any Hedging Agreements in respect of commodities if the notional volumes thereof (when aggregated with other commodity Hedging Agreements of the Borrower and other Subsidiaries then in effect)
exceed, as of the date such Hedging Agreement is executed, 75% of the projected production from Oil and Gas Properties for the period during which such Hedging Agreement is in effect.

SECTION
7.2.14Use of Proceeds.No proceeds of any Loan will be used to acquire any equity security of a class
which is publicly traded or is registered pursuant to Section 12 of the Securities Exchange Act of 1934 or any Margin Stock except in connection with transactions (a) authorized by the
board of directors of the Borrower, (b) either (i) authorized by the board of directors or other governing body of the Person which stock is being acquired, (ii) involving less
than 5% of the stock of any Person (except the Borrower), or (iii) where the Borrower or any of its Subsidiaries invest in the equity of the MLP, and (c) which would not cause the
Borrower to fail to be in compliance withSection 6.17and which would not cause the Loans or the Lenders to be in violation of
Regulation U.

SECTION
7.2.15Gas Imbalances, Take-or-Pay or Other Prepayments.The Parent will not
allow net gas imbalances in excess of 200,000 MMBTU of gas, take-or-pay or other prepayments with respect to the Oil and Gas Properties of the Parent or the
MarkWest Inc. Subsidiaries that would require the Parent or the MarkWest Inc. Subsidiaries to deliver Oil and Gas produced on Oil and Gas Properties at some future time without then or
thereafter receiving full payment therefore.

ARTICLE VIII
EVENTS OF DEFAULT

SECTION
8.1Listing of Events of Default.Each of the following events or occurrences described in this Section 8.1shall constitute an "Event of Default."

SECTION
8.1.1Non-Payment of Obligations.The Borrower shall default in the payment or prepayment
when due of any principal of or interest on any Loan, or the Borrower shall default (and such default
shall continue unremedied for a period of five days) in the payment when due of any Commitment Fee or of any other Obligation.

SECTION
8.1.2Breach of Warranty.Any representation or warranty of the Borrower or any other Obligor made or
deemed to be made hereunder or in any other Loan Document executed by it or any other writing or certificate furnished by or on behalf of the Borrower or any other Obligor to the Canadian
Administrative Agent or any Lender for the purposes of or in connection with this Agreement or any such other Loan Document (including any certificates delivered pursuant to Article V) is or shall
be incorrect when made in any material respect.

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SECTION
8.1.3Non-Performance of Certain Covenants and Obligations.The Borrower shall default in
the due performance and observance of any of its obligations underSection 7.1.1(d)or Section 7.2which default continues unremedied for ten
(10) days.

SECTION
8.1.4Non-Performance of Other Covenants and Obligations.Any Obligor shall default in the
due performance and observance of any other agreement, covenant or obligation contained herein or in any other Loan Document executed by it, and such default shall continue unremedied for a period of
thirty (30) days after notice thereof shall have been given to the Borrower by the Canadian Administrative Agent or any Lender.

SECTION
8.1.5Default Under Other Indebtedness or U.S. Credit Agreement.

(a)  The
Parent or any of the MarkWest Inc. Operating Subsidiaries (i) fails to make any payment when due (whether by scheduled maturity, required prepayment,
acceleration, demand or otherwise) in respect of any Indebtedness (other than Indebtedness hereunder or under the U.S. Credit Agreement) having an aggregate principal amount (including undrawn
committed or available amounts and including amounts owing to all creditors under any combined or syndicated credit arrangement) of more than U.S. $3,500,000 or (ii) fails to observe or perform
any other agreement or condition relating to any such Indebtedness or contained in any instrument or agreement evidencing, securing or relating thereto, or any other event occurs, the effect of which
default or other event is to cause, or to permit the holder or holders of such Indebtedness or a trustee or agent on behalf of such holder or holders to cause, with the giving of notice if required,
such Indebtedness to be demanded or to become due or to be repurchased or redeemed (automatically or otherwise) prior to its stated maturity; or

(b)  An
"Event of Default" occurs as defined in the U.S. Credit Agreement or in any replacement or refinancing thereof.

SECTION
8.1.6Judgments.

(a)  Any
final judgment or order for the payment of money in excess of U.S. $3,500,000 shall be rendered against the Parent or any of the MarkWest Inc. Operating
Subsidiaries and either (i) enforcement proceedings shall have been commenced by any creditor upon such judgment or order; or (ii) there shall be any period of 15 consecutive days during
which a stay of enforcement of such judgment or order, by reason of a pending appeal or otherwise, shall not be in effect.

(b)  Any
non-monetary final judgment shall be rendered that has, or would reasonably be expected to have, a Material Adverse Effect and, in either case,
(i) enforcement proceedings are commenced by any creditor upon such judgment or order, or (ii) there is a period of 15 consecutive days during which a stay of enforcement of such
judgment, by reason of a pending appeal or otherwise, is not in effect.

SECTION
8.1.7Default under Parent Guaranty.An Event of Default occurs as defined in the Parent Guaranty.

SECTION
8.1.8Control of the Borrower.Any Change in Control (Parent) or Change in Control (Canadian Borrower)
shall occur.

SECTION
8.1.9Bankruptcy, Insolvency, etc.The Parent or any of the MarkWest Inc. Operating Subsidiaries
shall (a) become insolvent or generally fail to pay, or admit in writing its inability or unwillingness to pay, debts as they become due; (b) apply for, consent to, or acquiesce in, the
appointment of a trustee, receiver, sequestrator or other custodian for the Parent or any of the MarkWest Inc. Operating Subsidiaries or any property of any thereof, or make a general
assignment for the benefit of creditors; (c) in the absence of such application, consent or acquiescence, permit or suffer to exist the appointment of a trustee, receiver, sequestrator or other
custodian for the Parent or any of the MarkWest Inc. Operating Subsidiaries or for a substantial part of the property of any thereof, and such trustee, receiver, sequestrator or other custodian
shall not be discharged within 60 days,provided,thatthe Parent and each MarkWest Inc.
Operating Subsidiaries hereby expressly

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authorizes each of the Canadian Administrative Agent and the Administrative Agent and each Lender to appear in any court conducting any relevant proceeding during such 60-day period to
preserve, protect and defend their rights under the Loan Documents; (d) permit or suffer to exist the commencement of any bankruptcy, reorganization, debt arrangement or other case or
proceeding under any bankruptcy or insolvency law including the Bankruptcy and Insolvency Act (Canada) and the Companies' Creditors Arrangement Act (Canada), as each are from time to time amended, or
any dissolution, winding up or liquidation proceeding, in respect of the Parent or any of the MarkWest Inc. Operating Subsidiaries or any other Obligor, and, if any such case or proceeding is
not commenced by the Parent or any MarkWest Inc. Operating Subsidiary, such case or proceeding shall be consented to or acquiesced in by the Parent or any MarkWest Inc. Operating
Subsidiary or shall result in the entry of an order for relief or shall remain for 60 days undismissed,provided, thatthe Parent or any of the
MarkWest Inc. Subsidiaries hereby expressly authorizes the Canadian Administrative Agent and the Administrative Agent and each Lender to appear in any court conducting any such case or
proceeding during such 60-day period to preserve, protect and defend their rights under the Loan Documents; or (e) take any corporate or partnership action authorizing, or in
furtherance of, any of the foregoing.

SECTION
8.1.10Impairment of Security, etc.Except as a direct result of the acts or omissions of the Canadian
Administrative Agent, the Administrative Agent or any Lender, any Loan Document, or any Lien granted thereunder, shall (except in accordance with its terms), in whole or in part, terminate, cease to
be effective or cease to be the legally valid, binding and enforceable obligation of any Obligor party thereto; the Borrower, any other Obligor or any other party shall, directly or indirectly,
contest in any manner such effectiveness, validity, binding nature or enforceability; or for a period of ten days following the earlier of the date the Borrower has knowledge thereof or the Borrower
receives notice from the Canadian Administrative Agent, the Administrative Agent or any Lender thereof, any Lien securing any Obligation shall, in whole or in part, cease to be a perfected first
priority Lien, subject only to those exceptions expressly permitted by such Loan Document.

SECTION
8.1.11Default Under Material Agreement.The Borrower or any of its Subsidiaries shall default in or
breach the performance or observance of any provision of any material contract or agreement to which it is a party or it or its property is bound if such default or breach could result in the opinion
of the Canadian Administrative Agent and the Required Lenders in a Material Adverse Effect and if such default or breach is not cured within thirty (30) days of the Borrower's knowledge of such
breach or default.

SECTION
8.1.12Invalidity of Loan Documents.Any Loan Document, at any time after its execution and delivery and
for any reason other than the agreement of the requisite percentage of Lenders or satisfaction in full of all the Obligations, ceases to be in full force and effect, or is declared by a court of
competent jurisdiction to be null and void, invalid or unenforceable in any respect; or any Obligor denies that it has any or further liability or obligation under any Loan Document, or purports to
revoke, terminate, rescind or invalidate any Loan Document in whole or in part.

SECTION
8.2Action if Bankruptcy.If any Event of Default described inclauses
(a)through(d)ofSection 8.1.9shall occur with respect to the Borrower
or any Obligor, the Revolving Loan Commitments (if not theretofore terminated) shall automatically terminate and the outstanding principal amount of all outstanding Loans and all other Obligations
shall automatically be and become immediately due and payable, without presentment, demand, protest, notice of intent to accelerate, notice of acceleration, notice of any other kind or demand.

SECTION
8.3Action if Other Event of Default.If any Event of Default (other than any Event of Default described
inclauses (a)through(d)ofSection 8.1.9with
respect to the Borrower or any other Obligor) shall occur for any reason, whether voluntary or involuntary, and be continuing, the Canadian Administrative Agent shall, upon the direction of, or may,
with the consent of, the Required Lenders, by notice to the Borrower (a) declare all or any portion of the outstanding principal amount of the

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Loans and other Obligations to be due and payable and/or the Revolving Loan Commitments (if not theretofore terminated) to be terminated, whereupon the full unpaid amount of such Loans and other
Obligations which shall be so declared due and payable shall be and become immediately due and payable, without notice of intent to accelerate, notice of acceleration, notice of any other kind,
protest, demand or presentment, and/or, as the case may be, the Revolving Loan Commitments shall terminate; (b) require that the Borrower Cash Collateralize its Obligations in respect of
Letters of Credit in an amount equal to 110% of the then aggregate Stated Amount of all Letters of Credit outstanding and undrawn; and (c) exercise on behalf of itself and the Lenders all
rights and remedies available to it and the Lenders under the Loan Documents or applicable law.

ARTICLE IX
THE AGENTS

SECTION
9.1Actions.Each Lender hereby appoints Bank of America, N.A., acting through its Canadian branch, as
its Canadian Administrative Agent, and appoints Bank of America, N.A. as its Administrative Agent under and for purposes of this Agreement, the Intercreditor Agreement, the Notes and each other Loan
Document. Each Lender authorizes each Agent to act on behalf of such Lender under this Agreement, the Intercreditor Agreement, the Notes and each other Loan Document and, in the absence of other
written instructions from the Required Lenders received from time to time by the Agents (with respect to which the Agents agree that they will comply, except as otherwise provided in this Section or
the Intercreditor Agreement or as otherwise advised by counsel), to exercise such powers hereunder and thereunder as are specifically delegated to or required of the Agents by the terms hereof and
thereof, together with such powers as may be reasonably incidental thereto. Each Lender hereby indemnifies (which indemnity shall survive any termination of this Agreement)each Agent, pro rataaccording
to such Lender's Percentage, from and against any and all liabilities, obligations, losses, damages, claims, costs or expenses of any
kind or nature whatsoever which may at any time be imposed on, incurred by, or asserted against, such Agent in any way relating to or arising out of this Agreement, the Intercreditor Agreement, the
Notes and any other Loan Document, including reasonable attorneys' fees, and as to which such Agent is not reimbursed by the Borrower;WHETHER OR NOT ARISING OUT OF THE
NEGLIGENCE OF SUCH AGENT,provided,however, that no Lender shall be liable for
the payment of any portion of such liabilities, obligations, losses, damages, claims, costs or expenses which are determined by a court of competent jurisdiction in a final proceeding to have resulted
solely from such Agent's gross negligence or wilful misconduct. Neither Agent shall be required to take any action hereunder, under the Intercreditor Agreement, the Notes or under any other Loan
Document, or to prosecute or defend any suit in respect of this Agreement, the Notes or any other Loan Document, unless it is indemnified to its satisfaction. If any indemnity in favor of an Agent
shall be or become, in such Agent's determination, inadequate, such Agent may call for additional indemnification from the Lenders and cease to do the acts indemnified against hereunder until such
additional indemnity is given.

SECTION
9.2Funding Reliance, etc.

(a)  Unless
the Canadian Administrative Agent shall have been notified by telephone, confirmed in writing, by any Lender by 10:30 p.m., Toronto, Ontario time, on the
day of a Borrowing that such Lender will not make available the amount which would constitute its Percentage of such Borrowing on the date specified therefor, the Canadian Administrative Agent may
assume that such Lender has made such amount available to the Canadian Administrative Agent and, in reliance upon such assumption, make available to the Borrower a corresponding amount. If and to the
extent that such Lender shall not have made such amount available to the Canadian Administrative Agent, such Lender and the Borrower severally agree to repay the Canadian Administrative Agent
forthwith on demand such corresponding amount together with interest thereon, for each day from the date the Canadian

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Administrative Agent made such amount available to the Borrower to the date such amount is repaid to the Canadian Administrative Agent, at the Canadian Cost of Funds Rate applicable at the time.

(b)  Unless
the Canadian Administrative Agent shall have been notified by telephone, confirmed in writing, by the Borrower prior to the date any payment to be made by it
hereunder is due, that it does not intend to remit such payment, the Canadian Administrative Agent may, in its sole and absolute discretion, assume that the Borrower has timely remitted such payment
and may, in its sole and absolute discretion and in reliance thereon, make available such payment to the Person entitled thereto. If such payment is not in fact remitted to the Canadian Administrative
Agent in immediately available funds, then each Lender shall forthwith on demand repay to the Canadian Administrative Agent the amount of such assumed payment made available to such Lender, together
with interest thereon in respect of each day from and including the date such amount was made available by the Canadian Administrative Agent to such Lender to the date such amount is repaid to the
Canadian Administrative Agent at the Canadian Cost of Funds Rate applicable at the time.

SECTION
9.3Exculpation.Neither Agent nor any of its directors, officers, employees or agents shall be liable
to any Lender for any action taken or omitted to be taken by it under this Agreement, the Intercreditor Agreement or any other Loan Document, or in connection herewith or therewith, except for its own
wilful misconduct or gross negligence, nor responsible for any recitals or warranties herein or therein, nor for the effectiveness, enforceability, validity or due execution of this Agreement or any
other Loan Document, nor for the creation, perfection or priority of any Liens purported to be created by any of the Loan Documents, or the validity, genuineness, enforceability, existence, value or
sufficiency of any collateral security, nor to make any inquiry respecting the performance by the Borrower of its obligations hereunder or under any other Loan Document. Any such inquiry which may be
made by an Agent shall not obligate it to make any further inquiry or to take any action. Each Agent shall be entitled to rely upon advice of counsel concerning legal matters and upon any notice,
consent, certificate, statement or writing which such Agent believes to be genuine and to have been presented by a proper Person.

SECTION
9.4Successor.The Canadian Administrative Agent may resign as such, and the Administrative Agent may
resign as such, in each case at any time upon at least thirty (30) days' prior notice to the Borrower and all Lenders. If either Agent at any time shall so resign, the Required Lenders may
appoint another Lender as a successor Canadian Administrative Agent, and may appoint another Lender or another lender under the U. S. Credit Agreement as successor Administrative Agent for the Lenders
hereunder, which shall thereupon become the Canadian Administrative Agent, or Administrative Agent, as applicable, hereunder. If no successor Canadian Administrative Agent (or, if applicable,
successor Administrative Agent) shall have been so appointed by the Required Lenders, and shall have accepted such appointment, within thirty (30) days after the retiring Agent's giving notice
of resignation, then the retiring Agent may, on behalf of the Lenders, appoint a successor Agent. In the case of a successor Canadian Administrative Agent, such successor shall be one of the Lenders
or a commercial banking institution organized under the laws of Canada, and having a combined capital and surplus of at least the Canadian Dollar Equivalent of U.S. $500,000,000. In the case of a
successor Administrative Agent, such successor shall be one of the Lenders or one of the Lenders as defined in the U.S. Credit Agreement or a commercial banking institution organized under the laws of
Canada or the United States, and having a combined capital and surplus of at least the Canadian Dollar Equivalent of U.S. $500,000,000. Notwithstanding the foregoing, so long as Canadian
Administrative Agent is a Schedule II Bank, Canadian Administrative Agent may appoint an Affiliate as successor Administrative Agent by providing prior written notice of such appointment to
Borrower, Administrative Agent, and Lenders. Upon the acceptance of any appointment as Canadian Administrative Agent (or, if applicable, successor Administrative Agent) hereunder by a successor
Canadian Administrative Agent (or, if applicable, successor Administrative Agent), such successor Agent shall be entitled to receive from the retiring Agent such documents of transfer and assignment

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as such successor Agent may reasonably request, and shall thereupon succeed to and become vested with all rights, powers, privileges and duties of the retiring Agent, and the retiring Agent shall be
discharged from its duties and obligations under this Agreement. After any retiring Agent's resignation hereunder, the provisions of (a) this Article IXshall inure to its benefit as to any
actions taken or omitted to be taken by it while it was an Agent under this Agreement; and
(b)Section 10.3andSection 10.4shall continue to inure to its benefit.

SECTION
9.5Loans by Bank of America, N.A.Bank of America, N.A. shall have the same rights and powers with
respect to (a) the Loans made by it or any of its Affiliates, and (b) the Notes held by it or any of its Affiliates as any other Lender and may exercise the same as if it were not an
Agent. Bank of America, N.A. and its Affiliates may accept deposits from, lend money to, and generally engage in any kind of business with the Borrower or any Subsidiary or Affiliate of the Borrower
as if Bank of America, N.A. were not an Agent hereunder.

SECTION
9.6Credit Decisions.Each Lender acknowledges that it has, independently of the Agents and each other
Lender, and based on such Lender's review of the financial information of the Borrower, this Agreement, the other Loan Documents (the terms and provisions of which being satisfactory to such Lender)
and such other documents, information and investigations as such Lender has deemed appropriate, made its own credit decision to extend its Revolving Loan Commitments. Each Lender also acknowledges
that it will, independently of the Agents and each other Lender, and based on such other documents, information and investigations as it shall deem appropriate at any time, continue to make its own
credit decisions as to exercising or not exercising from time to time any rights and privileges available to it under this Agreement or any other Loan Document.

SECTION
9.7Copies, etc.The Canadian Administrative Agent shall give prompt notice to each Lender of each
notice or request required or permitted to be given to the Canadian Administrative Agent by the Borrower pursuant to the terms of this Agreement (unless concurrently delivered to the Lenders by the
Borrower). The Canadian Administrative Agent will distribute to each Lender each document or instrument received for its account and copies of all other communications received by the Canadian
Administrative Agent from the Borrower for distribution to the Lenders by the Canadian Administrative Agent in accordance with the terms of this Agreement.

SECTION
9.8Default; Collateral.

(a)  Upon
the occurrence and continuance of a Default, the Lenders agree to promptly confer in order that Required Lenders or the Lenders, as the case may be, may agree upon
a course of action for the enforcement of the rights of the Lenders; and the Agents shall be entitled to refrain from taking any action (without incurring any liability to any Person for so
refraining)unlessand until the Agents shall have received instructions from Required Lenders. Subject to the Intercreditor Agreement for so long as it
is in effect, all rights of action under the Loan Documents and all right to the Collateral, if any, hereunder may be enforced by the Agents and any suit or proceeding instituted by the Agents in
furtherance of such enforcement shall be brought in its name as the applicable Agent without the necessity of joining as plaintiffs or defendants any other Lender, and the recovery of any judgment
shall be for the benefit of the Lenders (and, with respect to Lender Hedging Agreements, Affiliates, if applicable) subject to the expenses of the applicable Agent(s). In actions with respect to any
property of the Borrower or any other Obligor, the Agents are acting for the ratable benefit of each Lender (and, with respect to Lender Hedging Agreement, Affiliates, if applicable). Any and all
agreements to subordinate (whether made heretofore or hereafter) other indebtedness or obligations of Borrower to the Obligation shall be construed as being for the ratable benefit of each Lender
(and, with respect to Lender Hedging Agreement, Affiliates, if applicable).

(b)  Each
Lender authorizes and directs the Administrative Agent to enter into the Collateral Documents for the benefit of the Lenders (and, with respect to Lender Hedging
Agreement, Affiliates, if applicable). Except to the extent unanimity (or other percentage set forth inSection 10.1) is required

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hereunder, each Lender agrees that any action taken by the Required Lenders in accordance with the provisions of the Loan Documents, and the exercise by the Required Lenders of the power set forth
herein or therein, together with such other powers as are reasonably incidental thereto, shall be authorized and binding upon all of the Lenders.

(c)  Each
Agent is hereby authorized on behalf of all of the Lenders, without the necessity of any notice to or further consent from any Lender, from time to time to take any
action with respect to any Collateral or Collateral Documents which may be necessary to perfect and maintain perfected the Liens upon the collateral granted pursuant to the Collateral Documents.

(d)  Neither
Agent shall have any obligation whatsoever to any Lender or to any other Person to assure that the Collateral exists or is owned by any Obligor or is cared for,
protected, or insured or has been encumbered or that the Liens granted to either Agent have been properly or sufficiently or lawfully created, perfected, protected, or enforced, or are entitled to any
particular priority, or to exercise at all or in any particular manner or under any duty of care, disclosure, or fidelity, or to continue exercising, any of the Rights granted or available to the
Agents in this Agreement or in any of the Collateral Documents; it being understood and agreed that in respect of the Collateral, or any act, omission, or event related thereto, subject to the
Intercreditor Agreement, each Agent may act in any manner it may deem appropriate, in its sole discretion, given the such Agent's own interest in the Collateral as one of the Lenders and that such
Agent shall have no duty or liability whatsoever to any Lender, other than to act without gross negligence or willful misconduct.

(e)  The
Lenders hereby irrevocably authorize each Agent, at its option and in its discretion, to release any Lien granted to or held by such Agent upon any Collateral:
(i) constituting property in which no Obligor owned an interest at the time the Lien was granted or at any time thereafter; (ii) constituting property leased to an Obligor under a lease
which has expired or been terminated in a transaction permitted under the Loan Document or is about to expire and which has not been, and is not intended by such Obligor to be, renewed; and
(iii) consisting of an instrument evidencing Indebtedness pledged to such Agent (for the benefit of the Lenders), if the Indebtedness evidenced thereby has been paid in full. In addition, the
Lenders irrevocably authorize each Agent to release Liens upon Collateral as contemplated inSection 10.1(b), (c)or(d), or if approved, authorized, or ratified in writing by the requisite Lenders. Upon request by
an Agent at any time, the Lenders will confirm in writing such Agent's authority to release particular types or items of Collateral pursuant to this Section 9.8.

(f)    In
furtherance of the authorizations set forth in thisSection 9.8, each Lender hereby irrevocably appoints each
of the Canadian Administrative Agent and the Administrative Agent, its attorney-in-fact, with full power of substitution, for and on behalf of and in the name of each such
Lender, subject to the Intercreditor Agreement (i) to enter into Collateral Documents (including, without limitation, any appointments of substitute trustees under any Collateral Documents),
(ii) to take action with respect to the Collateral and Collateral Documents to perfect, maintain, and preserve Lenders' Liens, and (iii) to execute instruments of release or to take
other action necessary to release Liens upon any Collateral to the extent authorized in paragraph (e) hereof. This power of attorney shall be liberally, not restrictively, construed so as to
give the greatest latitude to each Agent's power, as attorney, relative to the Collateral matters described in thisSection 9.8. The powers and
authorities herein conferred on each Agent may be exercised by such Agent through any Person who, at the time of the execution of a particular instrument, is an officer of such Agent. The power of
attorney conferred by thisSection 9.8(f)is granted for valuable consideration and is coupled with an interest and is irrevocable so long as the
Obligations, or any part thereof, shall remain unpaid or the Lenders are obligated to make any Borrowings under the Loan Documents.

SECTION
9.9Lender Hedging Agreements.To the extent any Lender or any Affiliate of a Lender is a party to a
Lender Hedging Agreement in accordance with the requirements of the Loan

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Documents and accepts the benefits of the Liens in the Collateral arising pursuant to the Collateral Documents, such Lender (for itself and on behalf of any such Affiliates) shall be deemed
(a) subject to the Intercreditor Agreement, to appoint Bank of America, N.A., as its nominee and agent, to act for
and on behalf of such Lender or Affiliate thereof in connection with the Collateral Documents and (b) to be bound by the terms of this Article IX.

ARTICLE X
MISCELLANEOUS PROVISIONS

SECTION
10.1Waivers, Amendments, Release of Collateral, etc.(a) The provisions of this Agreement and of
each other Loan Document may from time to time be amended, modified or waived, if such amendment, modification or waiver is in writing and consented to by the Borrower and the Required Lenders; provided,however, that no such amendment, modification or waiver which would: (a) modify any
requirement hereunder that any particular action be taken by all the Lenders or by the Required Lenders shall be effective unless consented to by each Lender; (b) modify this Section 10.1,
change the definition of "Required Lenders," increase any Commitment Amount (except
as set forth inSection 2.5.1) or the Percentage of any Lender, reduce any fees described in Article III, release any material portion of the
Collateral, except as set forth in Section 9.8andSections 10.1(b),(c)and (d)or otherwise specifically provided in any Loan Document, release any material Guarantor (except as provided in Section 10.1(d)), or extend any Revolving Loan
Commitment Termination Date, shall be made without the consent of each Lender and each holder of a
Note; (c) extend the due date for, or reduce the amount of, any scheduled repayment or prepayment of principal of or interest on any Loan (or reduce the principal amount of or rate of interest
on any Loan) shall be made without the consent of the holder of that Note evidencing such Loan; (d) affect adversely the interests, rights or obligations of the Canadian Administrative Agent or
the Administrative Agent, shall be made without consent of the Canadian Administrative Agent or the Administrative Agent, as applicable; (e) affect adversely the interests, rights or
obligations of an Issuer in its capacity as such, shall be made without consent of such Issuer or (f) increase, maintain, or decrease the Canadian Borrowing Base pursuant to Section 2.1.3of
the U.S. Credit Agreement or this Agreement, as applicable, without the consent of the Lenders or increase, maintain, or
decrease the Global Borrowing Base pursuant toSection 2.1.3of the U.S. Credit Agreement without the consent of the Global Lenders (as defined
in the U.S. Credit Agreement). No failure or delay on the part of any Agent, any Lender or the holder of any Note in exercising any power or right under this Agreement or any other Loan Document shall
operate as a waiver thereof, nor shall any single or partial exercise of any such power or right preclude any other or further exercise thereof or the exercise of any other power or right. No notice
to or demand on the Borrower in any case shall entitle it to any notice or demand in similar or other circumstances. No waiver or approval by the Canadian Administrative Agent or the Administrative
Agent, any Lender or the holder of any Note under this Agreement or any other Loan Document shall, except as may be otherwise stated in such waiver or approval, be applicable to subsequent
transactions. No waiver or approval hereunder shall require any similar or dissimilar waiver or approval thereafter to be granted hereunder.

(b)  Upon
any sale, transfer, or disposition of Collateral which is permitted pursuant to the Loan Documents, and upon ten (10) Business Days' prior written request by
the Borrower (which request must be accompanied by (a) true and correct copies of all material documents of transfer or disposition, including any contract of sale, (ii) a preliminary
closing statement and instructions to the title company, if any, and (iii) all requested release instruments in form and substance satisfactory to the Administrative Agent), the Administrative
Agent shall (and is hereby irrevocably authorized by the Lenders to) execute such documents as may be necessary to evidence the release of Liens granted to
the Administrative Agent for the benefit of the Lenders pursuant hereto in such Collateral. The Administrative Agent shall not be required to execute any release instruments on terms which, in the
Administrative Agent's opinion, would expose the Administrative Agent to liability or create any

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obligation or entail any consequence other than the release of liens without recourse or warranty. No such release shall impair the Administrative Agent's lien on the proceeds of sale of such
Collateral.

(c)  If
all outstanding Loans and other Obligations have been paid in full and no Letters of Credit are outstanding, the Revolving Loan Commitments have terminated or have
been reduced to zero pursuant toSection 2.2, and, subject toSection 10.1(d), all Lender
Hedging Agreements have terminated, the Lenders hereby instruct the Canadian Administrative Agent and the Administrative Agent to, at the Borrower's expense, execute such releases of the Collateral
Documents as the Borrower shall reasonably request and this Agreement shall be deemed terminated except that such termination shall not relieve Borrower of any obligation to make any payments to the
Canadian Administrative Agent, the Administrative Agent or any Lender required by any Loan Document to the extent accruing, or relating to an event occurring, prior to such termination.
Notwithstanding the foregoing, if such Liens also secure the obligations under the U.S. Credit Agreement, such Liens may not be released unless permitted by the terms of U.S. Credit Agreement.

(d)  Notwithstanding
any provision herein to the contrary, if the Revolving Loan Commitments as herein defined and as defined in the U.S. Credit Agreement have been
terminated, no Letters of Credit hereunder or under the U.S. Credit Agreement are outstanding, and the only outstanding Obligations as herein defined and as defined in the U.S. Credit Agreement are
amounts owed pursuant to one or more Lender Hedging Agreements, the Administrative Agent and the Canadian Administrative Agent will, and are hereby authorized to, (A) release the Liens created
under the Loan Documents, and (B) release the Parent Guaranty and all Guaranties executed by the MarkWest Inc. Operating Subsidiaries, provided,thatcontemporaneously with such release, (i) the Parent executes a guaranty agreement
covering the obligations of the MarkWest Inc. Operating Subsidiaries that are parties to such Lender Hedging Agreements, such guaranty to be in form and substance satisfactory to the Lender(s)
or its Affiliates that are parties to such Lender Hedging Agreements (the "Lender Counterparties"), and (ii) each of the Borrower and the Parent
(A) executes a margin agreement in form and substance acceptable to such Lender Counterparties and (B) provides collateral in the form of cash or a letter of credit having an aggregate
value acceptable to such Lender Counterparties; andprovided further, the Borrower acknowledges that if such Liens and/or Guaranties also secure the
Obligations under the U.S. Credit Agreement, such Liens and Guaranties may not be released unless permitted by the U.S. Credit Agreement. Any release under this Section 10.1(d)must be in writing
and signed by the Administrative Agent or the Canadian Administrative Agent, as applicable.

SECTION
10.2Notices.All notices and other communications provided to any party hereto under this Agreement or
any other Loan Document shall be in writing or by facsimile and addressed, delivered or transmitted to such party at its address or facsimile number set forth, with respect to Borrower and Canadian
Administrative Agent, below its signature hereto, and with respect to any Lender, set forth in its Administrative Questionnaire provided to the Canadian Administrative Agent hereto or set forth in the
Lender Assignment Agreement, or as set forth in the Intercreditor Agreement with respect to the Administrative Agent, at such other address or facsimile number as may be designated by such party in a
notice to the other parties. Any notice, if mailed and properly addressed with postage prepaid or if
properly addressed and sent by pre-paid courier service, shall be deemed given when received; any notice, if transmitted by facsimile, shall be deemed given when transmitted.

SECTION
10.3Payment of Costs and Expenses.The Borrower agrees to pay within 10 days of demand all
reasonable expenses of each Agent (including the fees and out-of-pocket expenses of counsel to such Agent and of local counsel, if any, who may be retained by counsel to the
such Agent) in connection with the negotiation, preparation, execution and delivery of this Agreement and of each other Loan Document, including schedules and exhibits, and any amendments, waivers,
consents, supplements or other modifications to this Agreement or any other Loan Document as may from time to time hereafter be required, whether or not the transactions contemplated hereby are
consummated,

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the filing, recording, refiling or rerecording of any mortgage, any pledge agreement and any Security Agreement and/or any other lien or notice filings relating thereto and all amendments,
supplements and modifications to any thereof and any and all other documents or instruments of further assurance required to be filed or recorded or refiled or rerecorded by the terms hereof or of any
mortgage, any pledge agreement or any security agreement, and the preparation and review of the form of any document or instrument relevant to this Agreement or any other Loan Document.

The
Borrower further agrees to pay, and to save each Agent and the Lenders harmless from all liability for, any stamp or other similar taxes which may be payable in connection with the
execution or delivery of this Agreement, the borrowings hereunder, or the issuance of the Notes or any other Loan Documents. The Borrower also agrees to reimburse each Agent and each Lender upon
demand for all reasonable out-of-pocket expenses (including attorneys' fees and legal expenses) incurred by the such Agent or such Lender in connection with the enforcement of
any Obligations.

SECTION
10.4Indemnification.In consideration of the execution and delivery of this Agreement by each Lender
and the extension of the Revolving Loan Commitments, the Borrower hereby indemnifies, exonerates and holds each Agent and each of their respective Affiliates and each Lender and each of their
respective officers, directors, employees, attorneys and agents (collectively, the "Indemnified Parties") free and harmless from and against any and all
actions, causes of action, suits, losses, costs, liabilities and damages, and expenses incurred in connection therewith (irrespective of whether any such Indemnified Party is a party to the action for
which indemnification hereunder is sought), including reasonable attorneys' fees and disbursements and settlement costsINCLUDING INDEMNIFIED LIABILITIES ARISING OUT OF THE
NEGLIGENCE OF AN INDEMNIFIED PARTY(collectively, the "Indemnified Liabilities"), incurred by the Indemnified Parties or any of
them as a result of, or arising out of, or relating to (a) any transaction financed or to be financed in whole or in part, directly or indirectly, with the proceeds of any Loan; (b) the
entering into and performance of this Agreement and any other Loan Document by any of the Indemnified Parties; (c) any investigation, litigation or proceeding related to any acquisition or
proposed acquisition by the Borrower or any of its Subsidiaries of all or any portion of the stock or assets of any Person, whether or not such Agent or such Lender is party thereto; (d) any
investigation, litigation or proceeding related to any environmental cleanup, audit, compliance or other matter relating to the protection of the environment or the release by the Borrower or any of
its Subsidiaries of any Hazardous Material; or (e) the presence on or under, or the escape, seepage, leakage, spillage, discharge, emission, discharging or releases from, any real property
owned or operated by the Borrower or any Subsidiary thereof of any Hazardous Material (including any losses, liabilities, damages, injuries, costs, expenses or claims asserted or arising under
any Environmental Law), regardless of whether caused by, or within the control of, the Borrower or such Subsidiary, except for any such Indemnified Liabilities arising for the account of a particular
Indemnified Party by reason of the relevant Indemnified Party's gross negligence or wilful misconduct.

SECTION
10.5Survival.The obligations of the Borrower underSections
4.3,4.4,4.5,4.6, 10.3and10.4, and the obligations of the Lenders under Section 9.1, shall in each case survive any termination of this Agreement, the payment in full of all
Obligations and the termination of all
Revolving Loan Commitments. The representations and warranties made by each Obligor in this Agreement and in each other Loan Document shall survive the execution and delivery of this Agreement and
each such other Loan Document.

SECTION
10.6Severability.Any provision of this Agreement or any other Loan Document which is prohibited or
unenforceable in any jurisdiction shall, as to such provision and such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions
of this Agreement or such Loan Document or affecting the validity or enforceability of such provision in any other jurisdiction.

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SECTION 10.7Headings.The various headings of this Agreement and of each other Loan Document are inserted
for
convenience only and shall not affect the meaning or interpretation of this Agreement or such other Loan Document or any provisions hereof or thereof.

SECTION
10.8Execution in Counterparts.This Agreement may be executed by the parties hereto in several
counterparts, each of which shall be executed by the Borrower and the Canadian Administrative Agent and be deemed to be an original and all of which shall constitute together but one and the same
agreement.

SECTION
10.9Governing Law; Submission to Process.Except to the extent that the law of another jurisdiction is
expressly elected in a Loan Document, the Loan Documents shall be deemed contracts and instruments made under the laws of the Province of Alberta and shall be construed and enforced in accordance with
and governed by the laws of the Province of Alberta and the laws of Canada applicable thereto, without regard to principles of conflicts of law. Each of the parties hereby agrees that any legal action
or proceeding against such Borrower with respect to this Agreement, the Notes or any of the Loan Documents may be brought in the courts of the Province of Alberta and each party submits and attorns
to, the non-exclusive jurisdiction of the aforesaid courts. Each party waives any right to stay or to dismiss any action or proceeding brought before said courts on the basis of forum non
conveniens. Nothing herein shall affect the right of Lender to serve process in any other manner permitted by law or shall limit the right of Lender to bring proceedings against Borrower in the courts
of any other jurisdiction.

SECTION
10.10Successors and Assigns

(a)  The
provisions of this Agreement shall be binding upon and inure to the benefit of the parties hereto and their respective successors and assigns permitted hereby,
except that the Borrower may not assign or otherwise transfer any of its rights or obligations hereunder without the prior written consent of each Lender and no Lender may assign or otherwise transfer
any of its rights or obligations hereunder except (i) to an Eligible Assignee in accordance with the provisions of paragraph (b) of this Section, (ii) by way of participation in
accordance with the provisions of paragraph (d) of this Section or (iii) by way of pledge or assignment of a security interest subject to the restrictions of paragraph (f) of this
Section (and any other attempted assignment or transfer by any party hereto shall be null and void). Nothing in this Agreement, expressed or implied, shall be construed to confer upon any Person
(other than the parties hereto, their respective successors and assigns permitted hereby, Participants to the extent provided in paragraph (d) of this Section and, to the extent expressly
contemplated hereby,
the Related Parties of each of the Canadian Administrative Agent and the Lenders) any legal or equitable right, remedy or claim under or by reason of this Agreement.

(b)  Any
Lender may at any time assign to one or more Eligible Assignees all or a portion of its rights and obligations under this Agreement (including all or a portion of
its Revolving Loan Commitment and the Loans at the time owing to it)provided however, that any such assignments by a Lender shall be pro rata with any
assignment by such Lender or an Affiliate of such Lender of its interests in the Canadian Facility;provided furtherthat (i) except in the case
of an assignment of the entire remaining amount of the assigning Lender's Revolving Loan Commitment and the Loans at the time owing to it or in the case of an assignment to a Lender or an Affiliate of
a Lender or an Approved Fund with respect to a Lender, the aggregate amount of the Revolving Loan Commitment (which for this purpose includes Loans outstanding thereunder) or, if the applicable
Revolving Loan Commitment is not then in effect, the principal outstanding balance of the Loan of the assigning Lender subject to each such assignment (determined as of the date the Assignment and
Assumption with respect to such assignment is delivered to the Canadian Administrative Agent or, if "Trade Date" is specified in the Assignment and Assumption, as of the Trade Date) shall not be less
than Cdn. $5,000,000, respect of Revolving Loans and the Revolving Loan Commitment, unless each of the Canadian Administrative Agent and, so long as no Event of Default has occurred and is continuing,
the

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Borrower otherwise consents (each such consent not to be unreasonably withheld or delayed); (ii) each partial assignment shall be made as an assignment of a proportionate part of all the
assigning Lender's rights and obligations under this Agreement and the Canadian Credit Agreement with respect to the Loan or the Revolving Loan Commitment assigned; (iii) any assignment of a
Revolving Loan Commitment must be approved by the Canadian Administrative Agent and the L/C Issuing Lender unless the Person that is the proposed assignee is itself a Lender with a Revolving Loan
Commitment (whether or not the proposed assignee would otherwise qualify as an Eligible Assignee); and (iv) the parties to each assignment shall execute and deliver to the Canadian
Administrative Agent an Assignment and Assumption, together with a processing and recordation fee of $3,500.00,and the Eligible Assignee, if it shall
not be a Lender, shall deliver to the Canadian Administrative Agent an Administrative Questionnaire. Subject to acceptance and recording thereof by the Canadian Administrative Agent pursuant to
paragraph (c) of this Section, from and after the effective date specified in each Assignment and Assumption, the Eligible Assignee thereunder shall be a party to this Agreement and, to the
extent of the interest assigned by such Assignment and Assumption, have the rights and obligations of a Lender under this Agreement, and the assigning Lender thereunder shall, to the extent of the
interest assigned by such Assignment and Assumption, be released from its obligations under this Agreement (and, in the case of an Assignment and Assumption covering all of the assigning Lender's
rights and obligations under this Agreement, such Lender shall cease to be a party hereto) but shall continue to be entitled to the benefits of Sections 4.4, 4.5 and 4.6 with respect to facts and
circumstances occurring prior to the effective date of such assignment. Any assignment or transfer by a Lender of rights or obligations under this Agreement that does not comply with this paragraph
shall be treated for purposes of this Agreement as a sale by such Lender of a participation in such rights and obligations in accordance with paragraph (d) of this Section.

(c)  The
Canadian Administrative Agent, acting solely for this purpose as an agent of the Borrower, shall maintain at one of its offices in Dallas, Texas (or such other
location as may be specified by the Canadian Administrative Agent) a copy of each Assignment and Assumption delivered to it and a register for the recordation of the names and addresses of the
Lenders, and the Revolving Loan Commitments of, and principal amounts of the Loans owing to, each Lender pursuant to the terms
hereof from time to time (the "Register"). The entries in the Register shall be conclusive, and the Borrower, the Canadian Administrative Agent and the
Lenders may treat each Person whose name is recorded in the Register pursuant to the terms hereof as a Lender hereunder for all purposes of this Agreement, notwithstanding notice to the contrary. The
Register shall be available for inspection by the Borrower and any Lender, at any reasonable time and from time to time upon reasonable prior notice.

(d)  Any
Lender may at any time, without the consent of, or notice to, the Borrower or the Canadian Administrative Agent, sell participations to any Person (other than a
natural person or the Borrower or any of the Borrower's Affiliates or Subsidiaries) (each, a "Participant") in all or a portion of such Lender's rights
and/or obligations under this Agreement (including all or a portion of its Revolving Loan Commitment and/or the Loans owing to it);providedthat
(i) such Lender's obligations under this Agreement shall remain unchanged, (ii) such Lender shall remain solely responsible to the other parties hereto for the performance of such
obligations and (iii) the Borrower, the Canadian Administrative Agent and the other Lenders shall continue to deal solely and directly with such Lender in connection with such Lender's rights
and obligations under this Agreement. Any agreement or instrument pursuant to which a Lender sells such a participation shall provide that such Lender shall retain the sole right to enforce this
Agreement and to approve any amendment, modification or waiver of any provision of this Agreement;providedthat such agreement or instrument may
provide that such Lender will not, without the consent of the Participant, take any actions of the type described inclause (b)or (c)ofSection 10.1. Subject to paragraph (e) of this Section, the Borrower agrees that
each Participant shall be entitled to the benefits of Sections 4.4, 4.5, and 4.6 to the same extent as if it were a Lender and had acquired its interest by assignment pursuant to paragraph (b)
of this Section. To the extent permitted by law, each Participant also shall be entitled to the benefits of Section 4.9 as though

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it were a Lender, provided such Participant agrees to be subject to Section 4.8 as though it were a Lender.

(e)  A
Participant shall not be entitled to receive any greater payment under Sections 4.4, 4.5 and 4.6 than the applicable Lender would have been entitled to receive with
respect to the participation sold to such Participant, unless the sale of the participation to such Participant is made with the Borrower's prior written consent. A Participant that would be a Foreign
Lender if it were a Lender shall not be entitled to the benefits of Section 4.6 unless the Borrower is notified of the participation sold to such Participant and such Participant agrees, for
the benefit of the Borrower, to comply with Section 4.6 as though it were a Lender.

(f)    Any
Lender may at any time pledge or assign a security interest in all or any portion of its rights under this Agreement to secure obligations of such Lender, including
without limitation any pledge or assignment to secure obligations to a Federal Reserve Bank;providedthat no such pledge or assignment shall release
such Lender from any of its obligations hereunder or substitute any such pledgee or assignee for such Lender as a party hereto.

SECTION
10.11Other Transactions.Nothing contained herein shall preclude the Canadian Administrative Agent or
any other Lender from engaging in any transaction, in addition to those
contemplated by this Agreement or any other Loan Document, with the Borrower or any of its Affiliates in which the Borrower or such Affiliate is not restricted hereby.

SECTION
10.12Forum Selection and Consent to Jurisdiction.

(a)  THIS
AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAW OF THE PROVINCE OF ALBERTA AND THE FEDERAL LAWS OF CANADA APPLICABLE THEREIN.

(b)  ANY
LEGAL ACTION OR PROCEEDING WITH RESPECT TO THIS AGREEMENT OR ANY OTHER LOAN DOCUMENT MAY BE BROUGHT IN THE COURTS OF THE PROVINCE OF ALBERTA, AND BY EXECUTION AND
DELIVERY OF THIS AGREEMENT, EACH OF THE BORROWER, THE CANADIAN ADMINISTRATIVE AGENT AND THE LENDERS CONSENTS, FOR ITSELF, AND IN RESPECT OF ITS PROPERTY, TO THE NON-EXCLUSIVE JURISDICTION
OF THOSE COURTS. EACH OF THE BORROWER, THE CANADIAN ADMINISTRATIVE AGENT AND THE LENDERS IRREVOCABLY WAIVES ANY OBJECTION, INCLUDING ANY OBJECTION TO THE LAYING OF VENUE OR BASED ON THE GROUNDS OF FORUM NON
CONVENIENS, WHICH IT MAY NOW OR HEREAFTER HAVE TO THE BRINGING OF ANY ACTION OR PROCEEDING IN SUCH JURISDICTION IN RESPECT OF THIS AGREEMENT
OR ANY DOCUMENT RELATED HERETO. EACH OF THE BORROWER, THE CANADIAN ADMINISTRATIVE AGENT AND THE LENDERS WAIVES PERSONAL SERVICE OF ANY SUMMONS, COMPLAINT OR OTHER PROCESS, WHICH MAY BE MADE BY ANY
OTHER MEANS PERMITTED BY ALBERTA LAW.

SECTION
10.13Waiver of Jury Trial.THE CANADIAN ADMINISTRATIVE AGENT, THE LENDERS AND
THE BORROWER HEREBY KNOWINGLY, VOLUNTARILY AND INTENTIONALLY WAIVE ANY RIGHTS THEY MAY HAVE TO A TRIAL BY JURY IN RESPECT OF ANY LITIGATION BASED HEREON, OR ARISING OUT OF, UNDER, OR IN CONNECTION
WITH, THIS AGREEMENT OR ANY OTHER LOAN DOCUMENT, OR ANY COURSE OF CONDUCT, COURSE OF DEALING, STATEMENTS (WHETHER VERBAL OR WRITTEN) OR ACTIONS OF THE CANADIAN ADMINISTRATIVE AGENT, THE LENDERS OR THE
BORROWER. THE BORROWER ACKNOWLEDGES AND AGREES THAT IT HAS RECEIVED FULL AND SUFFICIENT CONSIDERATION FOR THIS PROVISION (AND EACH OTHER PROVISION OF EACH OTHER LOAN DOCUMENT TO WHICH IT IS A PARTY)
AND THAT THIS PROVISION IS

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A MATERIAL INDUCEMENT FOR THE CANADIAN ADMINISTRATIVE AGENT AND THE LENDERS ENTERING INTO THIS AGREEMENT AND EACH SUCH OTHER LOAN DOCUMENT.

SECTION
10.14Confidentiality.Each Lender and the Canadian Administrative Agent agrees to use reasonable
commercial efforts not to disclose without the prior written consent of the Borrower (other than to their employees, auditors or counsel or to another Lender if the Lender or such Lender's holding or
parent company or the Canadian Administrative Agent in its sole discretion determines that
any such party should have access to such information) any confidential information with respect to the Borrower or any Subsidiary which is furnished pursuant to this Agreement, provided, that any
Lender and the Canadian Administrative Agent may disclose any such information (a) as has become generally available to the
public, (b) as may be required or appropriate in any report, statement or testimony submitted to any municipal, provincial, state or Federal regulatory body having or claiming to have
jurisdiction over such Lender or the Canadian Administrative Agent or to the Federal Reserve Board, Bank of Canada, the Office of the Superintendent of Financial Institutions, Canada Deposit Insurance
Corporation, the Federal Deposit Insurance Corporation, National Association of Insurance Commissioners or similar organizations (whether in the United States or elsewhere) or their successors,
(c) as may be required or appropriate in response to any summons or subpoena or in connection with any litigation, (d) in order to comply with any law, order, regulation or ruling
applicable to such Lender or the Canadian Administrative Agent, and (e) to any Affiliate of such Lender or Canadian Administrative Agent.

A
Lender may furnish any publicly available information concerning the Borrower or any of its Subsidiaries in the possession of such Lender from time to time to assignees and
participants (including prospective assignees and participants) without the consent of the Borrower. Nonpublic information concerning the Borrower or any of its Subsidiaries shall not be furnished by
any Lender to assignees and participants (including prospective assignees and participants) without the prior written consent of the Borrower, which consent shall not be unreasonably withheld or
delayed.

SECTION
10.15[Intentionally Blank]

SECTION
10.16Priority of Hedging Obligations.Borrower, Lenders and the Agents agree that (a) any
amounts received in satisfaction of any Obligations arising under the Loan Documents, including, without limitation, Obligations under this Agreement, and any Lender Hedging Agreement, shall rank pari passuin right of payment and shall be used to repay such Obligations on a pro rata basis, and (b) all Hedging Obligations arising in
connection with any Hedging Agreement, other than any Lender Hedging Agreement, are hereby expressly subordinated in right of payment to the prior payment in full in cash of all Obligations under the
Loan Documents.

SECTION
10.17Certain Remedies.Notwithstanding anything to the contrary contained herein or in the Collateral
Documents, neither the Agents nor the Lenders shall have the right to collect income, rents, royalties, revenues, issues, profits or proceeds from the Mortgaged Properties as therein defined unless an
Event of Default has occurred and is continuing.

SECTION
10.18Maximum Rate.It is the intention of the parties hereto to comply strictly with applicable usury
laws, if any; accordingly, notwithstanding any provision to the contrary contained herein or in any fee letter or other Loan Document or any other document otherwise relating hereto, in no event shall
this Agreement or any Note or such documents require or permit the payment, taking, reserving, receiving, collection or charging of any sums constituting interest under applicable laws which exceed
the maximum amount permitted by such laws. If any such excess interest is called for, contracted for, charged, taken, reserved, or received in connection with any Loan or in any fee letter or other
Loan Document, or in any communication by the Canadian Administrative Agent, any
Lender or any other person to the Borrower or any other person, or in the event all or part of the principal or interest of any Loan shall be prepaid or accelerated, so that under any of such
circumstances or under any other circumstance whatsoever the amount of interest contracted for,

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charged, taken, reserved, or received on the amount of principal actually outstanding from time to time under this Agreement or any Note shall exceed the maximum amount of interest permitted by
applicable usury laws, then in any such event it is agreed as follows: (i) the provisions of this paragraph shall govern and control, (ii) neither the Borrower nor any other person or
entity now or hereafter liable for the payment of any Loan shall be obligated to pay the amount of such interest to the extent such interest is in excess of the maximum amount of interest permitted by
applicable usury laws, (iii) any such excess which is or has been received notwithstanding this paragraph shall be credited against the then unpaid principal balance of the Loans or, if the
Loans have been or would be paid in full by such credit, refunded to the Borrower, and (iv) the provisions of this Agreement, the Notes and the other Loan Documents, and any communication to
the Borrower, shall immediately be deemed reformed and such excess interest reduced, without the necessity of executing any other document, to the maximum lawful rate allowed under applicable laws as
now or hereafter construed by courts having jurisdiction hereof or thereof. Without limiting the foregoing, all calculations of the rate of interest contracted for, charged, collected, taken,
reserved, or received in connection herewith which are made for the purpose of determining whether such rate exceeds the maximum lawful rate shall be made to the extent permitted by applicable laws by
amortizing, prorating, allocating and spreading during the period of the full term of the Loans, including all prior and subsequent renewals and extensions, all interest at any time contracted for,
charged, taken, collected, reserved, or received. The terms of this paragraph shall be deemed to be incorporated in every Loan Document and communication relating to this Agreement, the Loans and the
Notes. In no event shall the aggregate "interest" (as defined in section 347 of the Criminal Code (Canada)) payable under the Loan Documents exceed the maximum effective annual rate of interest
on the "credit advanced" (as defined in that section) permitted under that section and, if any payment, collection or demand pursuant to this Agreement in respect of "interest" (as defined in that
section) is determined to be contrary to the provisions of that section, such payment, collection or demand shall be deemed to have been made by mutual mistake of Borrower, the Agents and Lenders and
the amount of such excess payment or collection shall be refunded to Borrower. For purposes of the Loan Documents, the effective annual rate of interest shall be determined in accordance with
generally accepted actuarial practices and principles over the term applicable to the Obligations on the basis of annual compounding of the lawfully permitted rate of interest and, in the event of
dispute, a certificate of a Fellow of the Canadian Institute of Actuaries appointed by Canadian Administrative Agent shall beprima facieevidence, for
the purposes of such determination.

SECTION
10.19Entire Agreement.

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

SECTION
10.20Annual Rates of Interest.For the purposes of the Interest Act (Canada), whenever interest payable
pursuant to this Agreement is calculated on the basis of a period other than a calendar
year (the "Interest Period"), each rate of interest determined pursuant to such calculation expressed as an annual rate is equivalent to such rate as so
determined multiplied by the actual number of days in the calendar year in which the same is to be ascertained anddivided bythe number of days in the
Interest Period.

SECTION
10.21Waiver of Judgment Interest Act (Alberta.To the extent permitted by Law, the provisions of the
Judgment Interest Act (Alberta) shall not apply to the Loan Documents and are hereby expressly waived by Borrower.

SECTION
10.22Deemed Reinvestment Not Applicable.For the purposes of the Interest Act (Canada), the principle
of deemed reinvestment of interest shall not apply to any interest calculation

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under the Loan Documents, and the rates of interest stipulated in this Agreement are intended to be nominal rates and not effective rates or yields.

SECTION
10.23Consent and Ratification of Collateral Documents.Each of the Borrower, the Parent, and the other
Guarantors (a) hereby consent to the execution and delivery of this Agreement, the Loan Documents, the U.S. Credit Agreement, and the Loan Documents as defined in the U.S. Credit Agreement,
(b) acknowledge that it has previously delivered to the Administrative Agent, pursuant to the terms and conditions of the Existing Credit Agreement, the Collateral Documents listed on Schedule 10.23hereto (the "Existing Collateral Documents), (c) confirm and agree that
each of the Existing Collateral Documents to which it is a party is, and shall continue to be, in full force and effect and shall secure the Obligations as herein defined and is hereby ratified and
confirmed in all respects except that, upon the effectiveness of, and on and after the date of, this Agreement, each reference in the Existing Collateral Documents to the Existing Credit Agreement,
shall mean and be a reference to this Agreement as amended, restated, or otherwise modified from time to time, and (d) all Notes issued pursuant to this Agreement shall be deemed to be issued
in replacement of the Notes issued under the Existing Credit Agreement and are, and shall continue to be, secured by the Existing Collateral Documents.

SECTION
10.24Assignment.The Existing Lenders, as holder of the Notes as defined in and issued under the
Existing Credit Agreement, hereby assign to the Lenders who are signatories hereto on the Effective Date, a portion of the indebtedness owed to each of them under the Existing Credit Agreement, so
that on the Effective Date all such Lenders have Revolving Loan Commitments and hold Loans in the Percentages set forth onSchedule 1.1(b)hereto.

SECTION
10.25Intercreditor Agreement; Agreement Regarding Collateral.The Lenders hereby authorize and instruct
the Administrative Agent and the Canadian Administrative Agent to enter into the Intercreditor Agreement and the Agreement Regarding Collateral, and each Lender agrees to be bound by all of the terms
and provisions of the Intercreditor Agreement and the Agreement Regarding Collateral to the same extent as if it were a signatory thereto.

SECTION
10.26Transfer of Assets to the MLP and Release of Liens and Guaranties Related Thereto.The
Administrative Agent, the Canadian Administrative Agent and the Lenders consent to the MLP Transfer, authorize the disposition of the assets described in the Contribution Agreement executed in
connection with the MLP Transfer free of their security interest and effective on the Effective Date, (a) each of Appalachia, West Shore, and Basin hereby are released from the Collateral
Documents executed by it in connection with the Existing Credit Agreement, (b) the Administrative Agent and the Lenders hereby release their liens and security interest on (i) the equity
interest in Appalachia, West Shore and Basin, and (ii) the liens and security interests on the other property being conveyed to the MLP Parties which other liens and security interests are
described onSchedule 10.20attached to the U.S. Credit Agreement under the heading "Liens Being Released on the Effective Date," and
(c) the Lenders authorize the Administrative Agent to execute such written releases as may be necessary to evidence such releases.

[SIGNATURES BEGIN ON FOLLOWING PAGE]

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IN
WITNESS WHEREOF, the parties hereto have caused this Agreement to be executed by their respective officers thereunto duly authorized as of the day and year first above written.

| |  | BORROWER:                      
| |  | -------------------------------
| |  | MARKWEST RESOURCES CANADA CORP.
| |  | By:                            
| |  |                                

| |  | Address for Notices: | 1340, 734 - 7th Avenue S.W.
Calgary, Alberta
T2P 3P8        
| |  | -------------------- | ------------------------------------------------------------
| |  | Telephone No:        | (403) 508-7410                                              
| |  | Facsimile No.:       | (403) 508-5285                                              
| |  | Attention:           | Chief Executive Officer                                     
| |  | with a copy to:     
| |  | Address for Notices: | 155 Inverness Drive West
Suite 200
Englewood, Colorado 80112
| |  | Telephone No.:       | (303) 290-8700                                              
| |  | Facsimile No.:       | (303) 290-8769                                              
| |  | Attention:           | Contract Administrator                                      

[THIS IS A SIGNATURE PAGE TO THE
MARKWEST RESOURCES CANADA CORP.
CREDIT AGREEMENT]

68

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| |  | GUARANTORS:               
| |  | --------------------------
| |  | MARKWEST HYDROCARBON, INC.
| |  | By:                       
| |  |                           

[THIS IS A SIGNATURE PAGE TO THE
MARKWEST RESOURCES CANADA CORP.
CREDIT AGREEMENT]

69

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| |  | MARKWEST MICHIGAN, INC.                   
| |  | ------------------------------------------
| |  | By:                                       
| |  |                                           
| |  | Name:                                     
| |  |                                           
| |  | Title:                                    
| |  |                                           
| |  | MARKWEST RESOURCES, INC.                  
| |  | By:                                       
| |  |                                           
| |  | Name:                                     
| |  |                                           
| |  | Title:                                    
| |  |                                           
| |  | MATREX, L.L.C.                            
| |  | By: MarkWest Resources, Inc., its Manger  
| |  | By:                                       
| |  |                                           
| |  | Name:                                     
| |  |                                           
| |  | Title:                                    
| |  |                                           
| |  | MARKWEST CANADIAN MIDSTREAM SERVICES, INC.
| |  | By:                                       
| |  |                                           
| |  | Name:                                     
| |  |                                           
| |  | Title:                                    
| |  |                                           

[THIS IS A SIGNATURE PAGE TO THE
MARKWEST RESOURCES CANADA CORP.
CREDIT AGREEMENT]

70

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| |  | BANK OF AMERICA, N.A.,[acting through its Canadian Branch],
as Canadian Administrative Agent and as a Lender
| |  | ------------------------------------------------------------------------------------------------------------
| |  | By:                                                                                                         
| |  |                                                                                                             

| |  | Address for Notices: | 200 Front Street West
Suite 2700
Toronto, Canada M5V 3L2              
| |  | -------------------- | ----------------------------------------------------------------------
| |  | Telephone No.:       | 416-349-5433                                                          
| |  | Facsimile No.:       | 416-349-4283                                                          
| |  | Attention:           | Ms. Medina Sales de Andrade                                           
| |  | with a copy to:      | Bank of America, N.A.
333 Clay Street, Suite 4550
Houston, Texas 77002
| |  | Telephone No.:       | (713) 651-4850                                                        
| |  | Facsimile No.:       | (713) 651-4841                                                        
| |  | Attention:           | Mr. Richard L. Stein                                                  

[THIS IS A SIGNATURE PAGE TO THE
MARKWEST RESOURCES CANADA CORP.
CREDIT AGREEMENT]

71

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| |  | LENDERS                        
| |  | -------------------------------
| |  | U.S. BANK, NATIONAL ASSOCIATION
| |  | By:                            
| |  |                                

[THIS IS A SIGNATURE PAGE TO THE
MARKWEST RESOURCES CANADA CORP.
CREDIT AGREEMENT]

72

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| |  | ROYAL BANK OF CANADA
| |  | --------------------
| |  | By:                 
| |  |                     

[THIS IS A SIGNATURE PAGE TO THE
MARKWEST RESOURCES CANADA CORP.
CREDIT AGREEMENT]

73

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| |  | WELLS FARGO BANK, N.A.
| |  | ----------------------
| |  | By:                   
| |  |                       

[THIS IS A SIGNATURE PAGE TO THE
MARKWEST RESOURCES CANADA CORP.
CREDIT AGREEMENT]

74

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