FIRST AMENDMENT TO
FOURTH AMENDED AND RESTATED CREDIT AGREEMENT

THIS FIRST AMENDMENT TO FOURTH AMENDED AND RESTATED CREDIT AGREEMENT (this "Amendment") is entered into as of
March 29, 2002, among MARKWEST HYDROCARBON, INC., a Delaware corporation (the "Borrower"), the undersigned Guarantors (the
"Guarantors"), BANK OF AMERICA, N.A., as Administrative Agent (the"Administrative
Agent")for the Lenders parties to the hereinafter defined Credit Agreement, and the undersigned Lenders.

Reference
is made to the Fourth Amended and Restated Credit Agreement dated as of October 12, 2001 (the"Credit Agreement") among
Borrower, Administrative Agent, and the Lenders parties thereto. Unless otherwise defined in this Amendment, capitalized terms used herein shall have the meaning set forth in the Credit Agreement; all
section and schedule references herein are to sections and schedules in the Credit Agreement; and all paragraph references herein are to paragraphs in this Amendment.

RECITALS

A.On the Effective Date as herein defined and immediately prior to the effectiveness of this Amendment, Bank of America,
N.A. is assigning a portion of its Commitment and its Loans to Royal Bank of Canada pursuant to a Lender Assignment Agreement.

B.The Borrower has requested certain amendments to the Credit Agreement in order to, among other things, (i) decrease
the amount of the Commitments, (ii) shorten the maturity, (iii) add a borrowing base, (iv) amend certain financial covenants, and (v) revise the amortization schedule.

C.Subject to the terms and conditions of this Amendment, the Administrative Agent and the undersigned Lenders are willing to
agree to such amendments.

Accordingly,
for adequate and sufficient consideration, the parties hereto agree, as follows:



1.1Definitions.

(a)  The
definition of "Accrued Columbia Settlement Balances" is inserted alphabetically into Section 1.1:



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(b)  The
definition of "Applicable Margin" is amended in its entirety to read as follows:



Applicable MarginPricing
Level

Leverage Ratio

LIBO Rate
Loan

Letter of
Credit

Base Rate Loan

Commitment Fee1

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.




(c)  The
following definition of "Available Borrowing Base" is inserted alphabetically into Section 1.1:



(d)  The
following definition of "Canadian Borrowing Base" is inserted alphabetically into Section 1.1:



(e)  The
definition of"Canadian Dollar Equivalent"is hereby amended to read as follows:



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(f)    The
following definition of "Canadian Effective Amount" is inserted alphabetically into Section 1.1:



(g)  The
following definition of "Eligible Midstream Accounts Receivable" is inserted alphabetically into Section 1.1:



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(h)  The
following definition of "Eligible Midstream Inventory" is inserted alphabetically into Section 1.1:



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(i)    The
definition of "Fixed Charge Coverage Ratio" is amended by (i) deleting the term "12 months" and
replacing it with the term "four Fiscal Quarters" and (ii) deleting each reference to the term "12-month" and replacing each such reference with the term "four-Fiscal
Quarter."

(j)    The
following definition of "Global Borrowing Base" is inserted alphabetically in Section 1.1:



(k)  The
following definition of "Global Lenders" is inserted alphabetically in Section 1.1:



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(l)    The
following definition of "Global Semi-Annual Borrowing Base" is inserted alphabetically into Section 1.1:



(m)  The
following definition of "Hedged Eligible Midstream Inventory" is inserted alphabetically into Section 1.1:



(n)  The
definition of "Leverage Ratio" is amended by (i) deleting the phrase "twelve months most recently
ended" and replacing it with the phrase "four Fiscal Quarters most recently ended" and (ii) deleting each reference to the term "12 months" and replacing each such reference with the
term "four Fiscal Quarters."

(o)  The
following definition of "Midstream Accounts Receivable" is inserted alphabetically into Section 1.1:



(p)  The
following definition of "Midstream Business" is inserted alphabetically into Section 1.1:



(q)  The
following definition of "Midstream Inventory" is inserted alphabetically into Section 1.1:



(r)  The
following definition of "Midstream Report" is inserted alphabetically into Section 1.1:



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(s)  The
following definition of "Required Global Lenders" is inserted alphabetically in Section 1.1:



(t)    The
definition of "Revolving Loan Commitment Amount" is amended by deleting the number "$55,000,000" and replacing it
with the number "$45,000,000."

(u)  The
definition of "Revolving Loan Commitment Termination Date" is amended by deleting the number "2005" and replacing it
with the number "2004."

(v)  The
following definition of "Semi-Annual Borrowing Base Period" is inserted alphabetically into Section 1.1:



(w)  The
definition of "Stated Maturity Date" is amended by deleting the number "2005" and replacing it with the number
"2004."

(x)  The
following definition of "U.S. Borrowing Base" is inserted alphabetically in Section 1.1:



(y)  The
definition of "U.S. Dollar Equivalent" is hereby amended to read as follows:



(z)  The
following definition of "U.S. Effective Amount" is inserted alphabetically into Section 1.1:



(aa) The
following definition of "U.S. Monthly Borrowing Base" is inserted alphabetically into Section 1.1:



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(bb) The
following definition of "U.S. Monthly Borrowing Base Certificate" is inserted alphabetically into Section 1.1:



(cc) The
following definition of "U.S. Semi-Annual Borrowing Base" is inserted alphabetically into Section 1.1:



(dd) The
following definition of "Unhedged Eligible Midstream Inventory" is inserted alphabetically into Section 1.1:



1.2Section 2.1.1(b). Section 2.1.1(b)is deleted in its
entirety and amended to read as follows:



1.3Section 2.1.3. Section 2.1.3is deleted in its entirety and amended to read as
follows:



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1.4.Section 2.1.5. Section 2.1.5is amended by deleting each reference to the term
"Revolving Loan Commitment Amount" and replacing each such reference with the
term "U.S. Borrowing Base less the aggregate amount of all Term Loans outstanding."

1.5Section 2.1.6.Section 2.1.6is
amended by (i) deleting the number "$75,000,000" and replacing it with the number "$65,000,000" and (ii) deleting the number "$110,000,000" and replacing it with the number
"100,000,000."

1.6Section 2.2.2. Section 2.2.2is amended by deleting the number "$3,667,000" and
replacing it with the number "$3,000,000."

1.7Section 3.1(b). Section 3.1(b)is deleted in its entirety and amended to read as
follows:



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Principal Payment Date

Term Loan CommitmentMarch 31, 2002

$37,200,000June 30, 2002

$34,400,000September 30, 2002

$30,287,500December 31, 2002

$25,725,000March 31, 2003

$21,162,500June 30, 2003

$16,600,000September 30, 2003

$12,037,500December 31, 2003

$10,532,800March 31, 2004

$  9,028,100June 30, 2004

$  7,523,400August 9, 2004

The remaining principal balance of the Term Loan


1.8Section 3.1.2. Section 3.1.2is deleted in its entirety and
amended to read as follows:



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1.9Section 3.3.2. Section 3.3.2is amended to add the following phrase immediately
prior to the period at the end of such section:



1.10Section 7.1.1(c). Section 7.1.1(c)is amended by deleting the term "month" and
replacing it with the term "Fiscal Quarter."

1.11Section 7.1.1(k). Section 7.1.1(k)is amended to read as follows:



1.12Section 7.1.1(m). Section 7.1.1is amended by re-designating clause (m) to be
clause (n) and adding the following Section 7.1.1(m):



1.13Section 7.1.8. Section 7.1.8is amended to add the
following phrase immediately prior to the period at the end of subsections (a) and (b):



1.14Section 7.2.4(a). Section 7.2.4(a)is amended by deleting each reference to the term
"month" and replacing each such reference with the term "Fiscal Quarter" and
deleting the term "after Closing" and replacing it with the term "after July 1, 2001."

1.15Section 7.2.4(b). Section 7.2.4(b)is amended by deleting the term "calendar month" and
replacing it with the term "Fiscal Quarter."

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para

1.16Section 7.2.4(c). Section 7.2.4(c)is deleted in its entirety and amended to read as
follows:



Maximum Leverage Ratio

As of the Date of
each Fiscal Quarter Ending
as Set Forth Below4.00

12/31/013.75

3/31/023.50

6/30/023.25

9/30/023.00

12/31/02 and Fiscal Quarters ending thereafter"


1.17Section 7.2.4(d). Section 7.2.4(d)is deleted in its entirety and amended to read as
follows:



Minimum Fixed Charge Coverage Ratio

As of the Date of
each Fiscal Quarter Ending
as Set Forth Below1.40

12/31/011.50

03/31/02 through 12/31/021.75

3/31/03 and thereafter"


1.18Section 7.2.9(b). Section 7.2.9(b)is deleted in its
entirety and amended to read as follows:



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1.19Section 7.2.15. A new Section 7.2.15is added to read as follows:



1.20Section 10.1(a). Section 10.1(a)is amended by deleting the word
"or" appearing immediately before subclause (e) thereof and inserting the following phrase
immediately after such subclause (e): "or (f) increase the Global Borrowing Base pursuant toSection 2.1.3without consent of the Global
Lenders,provided, the Required Global Lenders may maintain or decrease the Global Borrowing Base pursuant to Section 2.1.3."

1.21Schedule V. Schedule Vto the Credit Agreement is amended to read as set forth inSchedule Vattached
hereto.

1.22Exhibit F.Exhibit Fto the Credit Agreement is hereby amended to read asSchedule Vattached hereto.

1.23Exhibit N. Exhibit Nattached hereto hereby is added to the Credit Agreement.

Paragraph 2. Effective Date.Notwithstanding any contrary provision, this Amendment is not
effective until the date (the"Effective Date") the following conditions are satisfied:

(a)  The
Administrative Agent shall have received counterparts of this Amendment, executed by the Borrower, the Guarantors, and the Required Lenders.

(b)  The
Borrower shall have executed and delivered a new Note reflecting the Commitments as amended except that new Notes shall not be required for the Lenders whose
Commitments have not changed.

(c)  The
Administrative Agent shall have received counterparts of the Guaranty (MarkWest Energy Appalachia, L.L.C.), the Pledge and Security Agreement (MarkWest Energy
Appalachia, L.L.C.), and the Acknowledgment of Pledge, each executed by MarkWest Energy Appalachia, L.L.C. and the related financing statement.

(d)  The
Administrative Agent shall have received from the Borrower and each Guarantor a certificate dated as of the Effective Date of its secretary, assistant secretary,
manager or general partner as applicable (i) as to resolutions of its board of directors or managers or their equivalent authorizing the execution and performance of this Amendment, and
(ii) if the officer executing this

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Amendment is not named in the incumbency certificate delivered at the time of execution of the Credit Agreement, as to the incumbency and signature of said officer.

(e)  The
Administrative Agent shall have received a legal opinion from counsel to the Borrower and each Guarantor as to the due authorization, execution and delivery of this
Amendment.

(f)    The
"Effective Date" shall occur simultaneously as defined in the First Amendment to the Canadian Credit Agreement.

(g)  Fees
and expenses required to be paid pursuant to Paragraph 5 of this Amendment have been paid to the extent invoiced prior to the Effective Date.

(h)  The
Administrative Agent shall have received such other assurances, certificates, documents and consents as the Administrative Agent may require.

Paragraph 3. Acknowledgment and Ratification.As a material inducement to the Administrative
Agent and the Lenders to execute and deliver this Amendment, each of the Borrower and the Guarantors (a) consents to the agreements in this Amendment and (b) agrees and acknowledges that
the execution, delivery, and performance of this Amendment shall in no way release, diminish, impair, reduce, or
otherwise affect the respective obligations of the Borrower or any Guarantor under the Loan Documents to which it is a party, which Loan Documents shall remain in full force and effect, and all rights
thereunder are hereby ratified and confirmed.

Paragraph 4. Representations.As a material inducement to the Administrative Agent and the
Lenders to execute and deliver this Amendment, each of the Borrower and the Guarantors represents and warrants to the Administrative Agent and the Lenders that as of the Effective Date of this
Amendment and as of the date of execution of this Amendment, (a) all representations and warranties in the Loan Documents are true and correct in all material respects as though made on the
date hereof, except to the extent that any of them speak to a different specific date, and (b) no Default or Event of Default exists.

Paragraph 5. Expenses.The Borrower shall pay within ten (10) days of demand all
reasonable costs, fees, and expenses paid or incurred by the Administrative Agent incident to this Amendment, including, without limitation, the fees and expenses of the Administrative Agent's counsel
in connection with the negotiation, preparation, delivery, and execution of this Amendment and any related documents, filing and recording costs, and the costs of title insurance endorsements if
required.

Paragraph 6. Miscellaneous.This Amendment is a"Loan Document"referred to
in the Credit Agreement. The provisions relating to Loan Documents inArticle 10of the Credit Agreement are
incorporated in this Amendment by reference. Unless stated otherwise (a) the singular number includes the plural andvice versaand words of any
gender include each other gender, in each case, as appropriate, (b) headings and captions may not be construed in interpreting provisions, (c) this Amendment must be construed, and its
performance enforced, under Texas law and applicable U.S. federal law, (d) if any part of this Amendment is for any reason found to be unenforceable, all other portions of it nevertheless
remain enforceable, and (e) this Amendment may be executed in any number of counterparts with the same effect as if all signatories had signed the same document, and all of those counterparts
must be construed together to constitute the same document.

Paragraph 7. Entire Agreement.This Amendment represents the final
agreement between the parties about the subject matter of this Amendment 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.

Paragraph 8. Parties.This Amendment binds and inures to the benefit of the Borrower, the
Guarantors, the Administrative Agent, the Lenders, and their respective successors and assigns.

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Paragraph 9. Further Assurances.The parties hereto each agree to execute from time to time
such further documents as may be necessary to implement the terms of this Agreement.

The
parties hereto have executed this Amendment in multiple counterparts to be effective as of the Effective Date.

Remainder of Page Intentionally Blank.
Signature Pages to Follow.

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| |  | BORROWER                                                                   
| |  | ---------------------------------------------------------------------------
| |  | MARKWEST HYDROCARBON, INC.                                                 
| |  | By:                                                                        
| |  | GUARANTORS                                                                 
| |  | MARKWEST MICHIGAN, INC., a Colorado corporation                            
| |  | By:                                                                        
| |  | MARKWEST RESOURCES, INC., a Colorado corporation                           
| |  | By:                                                                        
| |  | WEST SHORE PROCESSING COMPANY, L.L.C., a Michigan limited liability company
| |  | By: Markwest Michigan, Inc., its Manager                                   
| |  | By:                                                                        
| |  |                                                                            
| |  | Name:                                                                      
| |  |                                                                            
| |  | Title:                                                                     
| |  |                                                                            
| |  | BASIN PIPELINE, L.L.C., a Michigan limited liability company               
| |  | By: Markwest Michigan, Inc., its Manager                                   
| |  | By:                                                                        
| |  |                                                                            
| |  | Name:                                                                      
| |  |                                                                            
| |  | Title:                                                                     
| |  |                                                                            

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| |  | MATREX, L.L.C., a Michigan limited liability company                    
| |  | ------------------------------------------------------------------------
| |  | By: Markwest Resources, Inc., its Manager                               
| |  | By:                                                                     
| |  |                                                                         
| |  | Name:                                                                   
| |  |                                                                         
| |  | Title:                                                                  
| |  |                                                                         
| |  | MARKWEST ENERGY APPALACHIA, L.L.C., a Delaware limited liability company
| |  | By: MarkWest Hydrocarbon, Inc., a Delaware corporation, its sole member 
| |  | By:                                                                     
| |  |                                                                         
| |  | Name:                                                                   
| |  |                                                                         
| |  | Title:                                                                  
| |  |                                                                         
| |  | BANK OF AMERICA, N.A., as Administrative Agent and as a Lender          
| |  | By:                                                                     
| |  | U.S. BANK, NATIONAL ASSOCIATION, as a Lender                            
| |  | By:                                                                     
| |  |                                                                         
| |  | Name:                                                                   
| |  |                                                                         
| |  | Title:                                                                  
| |  |                                                                         

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