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                                                                  EXHIBIT 10.2

2d Draft of April 30, 2002

                            CONTRIBUTION, CONVEYANCE
                            AND ASSUMPTION AGREEMENT

     THIS CONTRIBUTION, CONVEYANCE AND ASSUMPTION AGREEMENT, dated as of May __,
2002, is entered into by and among MARKWEST ENERGY PARTNERS, L.P., a Delaware
limited partnership ("MLP"), MARKWEST ENERGY OPERATING COMPANY, L.L.C., a
Delaware limited liability company ("OLP"), MARKWEST ENERGY GP, L.L.C., a
Delaware limited liability company ("GP"), MARKWEST MICHIGAN, INC., a Michigan
corporation ("MICHIGAN"), MARKWEST ENERGY APPALACHIA, L.L.C., a Delaware limited
liability company ("MEA"), WEST SHORE PROCESSING COMPANY, L.L.C., a Michigan
limited liability company ("WEST SHORE") and MARKWEST HYDROCARBON, INC., a
Delaware corporation ("MARKWEST"). Capitalized terms used herein shall have the
meanings assigned to such terms in Section 1.1.

                                    RECITALS

     A. MarkWest and GP have formed MLP pursuant to the Delaware Revised Uniform
Limited Partnership Act (the "DELAWARE ACT"), for the purpose of, among other
things, serving as the managing member of OLP, and engaging in any business
activity permitted to be engaged in by GP and OLP pursuant to the Limited
Liability Company Agreement of OLP, including, without limitation, indirectly
acquiring, owning and operating certain of the assets of MarkWest, and of
certain subsidiaries of MarkWest, used in extracting, processing, fractionating,
storing, transporting and distributing natural gas liquid.

     B. In order to accomplish the objectives and purposes in the preceding
recital, the following actions have been taken prior to the date hereof pursuant
to that certain Contribution Agreement dated May ___, 2002:

          1. MarkWest has formed MEA, to which MarkWest contributed $1,000 in
exchange for all of the membership interests in MEA.

          2. MarkWest has formed GP, to which MarkWest contributed $1,000 in
exchange for all of the membership interests in GP.

          3. MarkWest and GP have formed MLP, to which MarkWest contributed $980
in exchange for a 98% limited partner interest in MLP, and GP contributed $20 in
exchange for a 2% general partner interest in MLP.

          4. The MLP has formed OLP, to which MLP contributed $1000 in exchange
for all of the membership interests in OLP.

     C. Concurrently with the consummation of the transactions contemplated
hereby, each of the following matters shall occur:

          1. MarkWest will contribute the Assets to MEA as a capital
contribution in exchange for a continuation of MarkWest's 100% membership
interest in MEA and the assumption by MEA of the MarkWest Liabilities.

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          2. MarkWest will contribute the MEA Interest to GP as a capital
contribution.

          3. GP will contribute the MEA Interest to MLP in exchange for (a) a
continuation of its 2% general partner interest in MLP, (b) the issuance of the
IDRs, (c) 1,792,000 Sub Units representing a 35.1% interest in MLP, (d) the
right to receive $20,100,000 of the proceeds of the OLP Debt, and (e) the right
to receive $16,100,000 for reimbursement of capital expenditures.

          4. Michigan will contribute the Basin Interest and the West Shore
Interest to MLP in exchange for (a) 1,208,000 Sub Units representing a 23.7%
interest in MLP, (b) the assumption by MLP of the Michigan Debt, and (c) the
right to receive $400,000 for reimbursement of capital expenditures.

          5. The public, through the Underwriters, will contribute $40,000,000
in cash, less the Underwriters' spread of $2,800,000, in exchange for 2,000,000
Common Units, representing a 39.2% interest in MLP.

          6. MLP will (a) pay transaction expenses associated with the
Acquisition in the amount of $3,200,000 (exclusive of the Underwriter's spread),
(b) contribute $4,300,000 to Basin, as a capital contribution, which Basin shall
use to retire Basin's debt of $4,300,000; (c) retire the Michigan Debt assumed
by MLP; and (d) reimburse GP $9,900,000 of capitalized expenditures.

          7. MLP will contribute its remaining cash (approximately $4,600,000)
and the MEA Interest, Basin Interest and West Shore Interest to OLP as a capital
contribution in exchange for a continuation of its 100% membership interest in
OLP.

          8. West Shore will distribute its membership interest in Basin to OLP.

          9. OLP will incur the OLP Debt.

          10. OLP will distribute $26,700,000 of the proceeds of the OLP Debt to
MLP and the OLP shall retain $2,800,000 of the proceeds of the OLP Debt for
working capital purposes.

          11. MLP will distribute $26,300,000 of the funds received from the OLP
Debt to GP, of which distribution a portion equal to $6,200,000 is in
reimbursement of capital expenditures.

          12. MLP will distribute $400,000 to Michigan in reimbursement of
capital expenditures.

          13. The GP will distribute its Sub Units and $36,200,000 of the funds
received from the MLP to MarkWest.

          14. MarkWest will sell 24,864 Sub Units to the Management Group for
$397,824.00.

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          15. MarkWest will sell 8.6% of its interest in GP to the Management
Group for $175,440.

          16. If the Underwriters exercise their over allotment option (the
"OPTION") to purchase up to 300,000 Common Units, the proceeds of that exercise,
net of the applicable underwriter's spread, shall be used to retire a portion of
the OLP Debt in reimbursement of capital expenditures of MarkWest.

          17. The Agreement of Limited Partnership of MLP, the Limited Liability
Company Agreement of OLP and the Limited Liability Company Agreement of GP will
be amended and restated to reflect the applicable matters set forth above and as
contained in this Agreement.

     D. In connection with the above described transactions, certain of the
parties have agreed to indemnify other of the parties from and against certain
liabilities.

     NOW, THEREFORE, in consideration of their mutual undertakings and
agreements hereunder, MLP, OLP, GP, Michigan, MEA, West Shore and MarkWest
undertake and agree as follows:

                                   ARTICLE 1
                                   DEFINITIONS

     Section 1.1 The following capitalized terms shall have the meanings given
below.

          (a) "ACQUISITION" means consummation of the transactions contemplated
by the terms of this Agreement.

          (b) "AGREEMENT" means this Contribution, Conveyance and Assumption
Agreement.

          (c) "ASSETS" means all right, title and interest of MarkWest in and
to the properties and assets set forth in EXHIBIT A attached hereto,
including all assets of every kind, character and description, whether
tangible or intangible, whether real, personal or mixed, whether accrued or
contingent, and wherever located, including, without limitation, all of the
assets necessary to operate the Business, and all right title and interest of
MarkWest to the following:

               (1) any and all rights, claims and causes of action that MarkWest
     may have under insurance policies or otherwise against any person or
     property, whether known or unknown, accrued or contingent, and whether or
     not reflected on the books and records of MarkWest, insofar as any of the
     same relate to the operation of the assets set forth in EXHIBIT A or the
     Business;

               (2) all know-how, every trade secret, every customer list and all
     other confidential information of every kind relating to the foregoing
     properties and rights; and

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               (3) all governmental licenses, permits and authorizations of
     every kind owned or held by MarkWest in connection with the ownership or
     operation of the foregoing properties and rights.

          (d) "ASSUMED LIABILITIES" means, collectively, the MarkWest
Liabilities and the Michigan Liabilities, excluding, however, the "Covered
Environmental Losses" as defined in the Omnibus Agreement.

          (e) "BASIN" means Basin Pipeline, L.L.C., a Michigan limited liability
company.

          (f) "BASIN INTEREST" means Michigan's membership interests in Basin
prior to the Effective Time.

          (g) "BUSINESS" means the gas extraction, processing and fractionation
activities of MarkWest as the same was operated immediately prior to the
Acquisition, but expressly excluding (1) marketing of natural gas liquids and
fractionated products, (2) oil and gas exploration and production activities,
and (3) gas gathering, treating and compressing activities related to oil and
gas exploration and production activities.

          (h) "CLAIMS" means any and all claims, demands, costs, liabilities
(including, without limitation, liabilities arising by way of active or passive
negligence) and expenses (including court costs and reasonable attorneys' fees)
of every kind, character and description, whether known or unknown, accrued or
contingent, and whether or not reflected on the books and records of MarkWest.

          (i) "COMMON UNIT" has the meaning assigned to such term in the
Partnership Agreement.

          (j) "CONVEYANCE DOCUMENTS" means the documents attached hereto as
[EXHIBIT B-1 AND EXHIBIT B-2] from MarkWest to MEA, dated the date of this
Agreement. MarkWest may execute and deliver multiple Conveyance Documents as
desirable to expedite recording thereof in the various jurisdictions in which
the Assets are located.

          (k) "DELAWARE ACT" has the meaning assigned to such term in Recital A
of this Agreement.

          (l) "EFFECTIVE TIME" shall mean 11:00 a.m. New York, New York time on
May __, 2002.

          (m) "EXCLUDED LIABILITIES" means (1) all of the income tax liabilities
of MarkWest and Michigan, and (2) all of the liabilities arising from or related
to MarkWest's ownership or operation of the Assets and Michigan's ownership of
the Basin Interest and West Shore Interest prior to the Effective Time;
provided, Excluded Liabilities does not include "Covered Environmental Losses"
as defined in the Omnibus Agreement.

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          (n) "GP" has the meaning assigned to such term in the opening
paragraph of this Agreement.

          (o) "IDRS" means "Incentive Distribution Rights" as such term is
defined in the Partnership Agreement.

          (p) "LAWS" means any and all laws, statutes, ordinances, rules or
regulations promulgated by a governmental authority, orders of a governmental
authority, judicial decisions, decisions of arbitrators or determinations of any
governmental authority or court.

          (q) "LIMITED PARTNER INTEREST" has the meaning assigned to such term
in Section 2.2 hereof.

          (r) "MANAGEMENT GROUP" means the individuals listed in EXHIBIT C
hereto.

          (s) "MARKWEST" has the meaning assigned to such term in the opening
paragraph of this Agreement.

          (t) "MARKWEST LIABILITIES" means all liabilities, including the
MarkWest Trade Payables, arising out of or related to the ownership or operation
of the Assets, or the ownership or conduct of MEA, to the extent arising or
accruing on and after the Effective Time, whether known or unknown, accrued or
contingent, and whether or not reflected on the books and records of MarkWest,
except the Excluded Liabilities.

          (u) "MARKWEST TRADE PAYABLES" means the current trade payables owed by
MarkWest in the amount of $4,600,000.

          (v) "MEA" has the meaning assigned to such term in the opening
paragraph of this Agreement.

          (w) "MEA INTEREST" means the membership interests in MEA.

          (x) "MICHIGAN" has the meaning assigned to such term in the opening
paragraph of this Agreement.

          (y) "MICHIGAN DEBT" means debt owed by Michigan in the amount of
     $15,200,000.

          (z) "MICHIGAN LIABILITIES" means all of the liabilities, including
the Michigan Debt, arising out of or related to the ownership or operation of
Basin and West Shore, or the Basin Interest and West Shore Interest, to the
extent arising or accruing on and after the Effective Time, whether known or
unknown, accrued or contingent, and whether or not reflected on the books and
records of Michigan, except the Excluded Liabilities.

          (aa) "MLP" has the meaning assigned to such term in the opening
paragraph of this Agreement.

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          (bb) "OLP" has the meaning assigned to such term in the opening
paragraph of this Agreement.

          (cc) "OLP DEBT" means new borrowing on debt by OLP in the approximate
amount of $29,500,000, which shall be nonrecourse to MarkWest and its
subsidiaries; provided, however, such debt shall be with recourse to GP and MLP.

          (dd) "OMNIBUS AGREEMENT" means that certain Omnibus Agreement of even
date herewith, among MarkWest, GP, MLP and OLP.

          (ee) "OPTION" has the meaning assigned to such term in Recital C16 of
this Agreement.

          (ff) "PARTNERSHIP AGREEMENT" means the Amended and Restated Agreement
of Limited Partnership of MarkWest Energy Partners, L.P. dated as of
______________, 2002.

          (gg) "RESTRICTION" has the meaning assigned to such term in Section
9.2 hereof.

          (hh) "RESTRICTION-ASSET" has the meaning assigned to such term in
Section 9.2 hereof.

          (ii) "SUB UNIT" means "Subordinated Unit" as such term is defined in
the Partnership Agreement.

          (jj) "UNDERWRITERS" means A.G. Edwards & Sons, Inc., RBC Capital
Markets and McDonald Investments, Inc.

          (kk) "WEST SHORE" has the meaning assigned to such term in the opening
paragraph of this Agreement.

          (ll) "WEST SHORE INTEREST" means Michigan's membership interests in
West Shore prior to the Effective Time.

                                   ARTICLE 2
                CONTRIBUTIONS, ACKNOWLEDGMENTS AND DISTRIBUTIONS

     Section 2.1 CONTRIBUTION OF THE ASSETS BY MARKWEST TO MEA. MarkWest hereby
grants, contributes, bargains, sells, conveys, assigns, transfers, sets over and
delivers to MEA, its successors and assigns, for its and their own use forever,
all right, title and interest of MarkWest in and to the Assets in exchange for
(a) the continuation of MarkWest's 100% membership interest in MEA, (b) the
assumption by MEA of the MarkWest Liabilities as set forth in Section 4.1
hereof, and (c) other good and valuable consideration, the sufficiency of which
is hereby acknowledged, and MEA hereby accepts the Assets as a contribution to
the capital of MEA. To further evidence this conveyance with respect to the real
property included in the Assets, MarkWest will execute and deliver the
Conveyance Documents to MEA.

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TO HAVE AND TO HOLD the Assets unto MEA, its successors and assigns, together
with all and singular the rights and appurtenances thereto in any way belonging,
subject, however, to the terms and conditions stated in this Agreement, forever.

     Section 2.2 CONTRIBUTION OF THE MEA INTEREST BY MARKWEST TO GP. MarkWest
hereby grants, contributes, bargains, sells, conveys, assigns, transfers, sets
over and delivers to GP, its successors and assigns, for its and their own use
forever, all right, title and interest of MarkWest in and to the MEA Interest in
exchange for (a) the continuation of MarkWest's membership interest in GP, and
(b) other good and valuable consideration, the sufficiency of which is hereby
acknowledged, and GP hereby accepts the MEA Interest as a contribution to the
capital of GP.

     Section 2.3 CONTRIBUTION OF THE MEA INTEREST BY GP TO MLP. GP hereby
grants, contributes, bargains, sells, conveys, assigns, transfers, sets over and
delivers to MLP, its successors and assigns, for its and their own use forever,
all right, title and interest of GP in and to the MEA Interest in exchange for
(a) a continuation of its 2% general partner interest in MLP, (b) the issuance
of the IDRs, (c) 1,792,000 Sub Units representing a 35.1% interest in MLP, (d)
the right to receive $20,100,000 from MLP sourced from the OLP Debt, (e) the
right to receive $16,100,000 in reimbursement of capital expenditures, and (f)
other good and valuable consideration, the sufficiency of which is hereby
acknowledged, and MLP hereby accepts the MEA Interest as a contribution to the
capital of MLP.

     Section 2.4 CONTRIBUTION OF THE BASIN INTEREST AND WEST SHORE INTEREST BY
MICHIGAN TO MLP. Michigan hereby grants, contributes, bargains, sells, conveys,
assigns, transfers, sets over and delivers to MLP, its successors and assigns,
for its and their own use forever, all right, title and interest of Michigan in
and to the Basin Interest and West Shore Interest in exchange for (a) 1,208,000
Sub Units representing a 23.7% interest in MLP, (b) the assumption by MLP of the
Michigan Debt, (c) the assumption by MLP of the Michigan Liabilities as set
forth in Section 4.2 hereof, (d) the right to receive $400,000 in reimbursement
of capital expenditures, and (e) other good and valuable consideration, the
sufficiency of which is hereby acknowledged, and MLP hereby accepts the Basin
Interest and West Shore Interest as a contribution to the capital of MLP.

     Section 2.5 PUBLIC CASH CONTRIBUTION. The parties to this Agreement
acknowledge a cash contribution by the public through the Underwriters to MLP of
$40,000,000 ($37,200,000 net to MLP after the underwriters' spread of
$2,800,000) in exchange for 2,000,000 Common Units, representing a 39.2%
interest in MLP.

     Section 2.6 PAYMENT OF TRANSACTION COSTS; RETIREMENT OF MICHIGAN DEBT. The
parties to this Agreement acknowledge (a) payment by MLP, in connection with the
Acquisition, of transaction expenses in the amount of $3,200,000, (b) retirement
by MLP of the Michigan Debt, and (c) reimbursement by MLP to GP of $9,900,000
for capital expenditures.

     Section 2.7 CONTRIBUTION OF CASH BY MLP TO BASIN. MLP hereby contributes to
Basin, its successors and assigns, for its and their own use forever, $4,300,000
in exchange for (a) a continuation of MLP's membership interest in Basin and (b)
other good and valuable

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consideration, the sufficiency of which are hereby acknowledged, and Basin
hereby accepts such sum as a contribution to the capital of Basin, which shall
be used to retire the debt of Basin.

     Section 2.8 CONTRIBUTION OF CASH AND THE MEA INTEREST, BASIN INTEREST AND
WEST SHORE INTEREST BY MLP TO OLP. The MLP hereby grants, contributes, bargains,
sells, conveys, assigns, transfers, sets over and delivers to OLP, its
successors and assigns, for its and their own use forever, all of its remaining
cash and all right, title and interest of MLP in and to the MEA Interest, Basin
Interest and West Shore Interest in exchange for (a) a continuation of its 100%
membership interest in OLP, and (b) other good and valuable consideration, the
sufficiency of which is hereby acknowledged, and OLP hereby accepts the cash and
the MEA Interest, Basin Interest and West Shore Interest as a contribution to
the capital of OLP.

     Section 2.9 DISTRIBUTION BY WEST SHORE OF INTERESTS IN BASIN TO OLP. West
Shore hereby grants, contributes, bargains, sells, convey, assigns, transfers,
sets over and delivers to OLP, its successors and assigns, for its and their own
use forever, all if West Shore's membership interests in Basin, and OLP hereby
accepts the membership interests in Basin.

     Section 2.10 BORROWING OF THE OLP DEBT. The parties to this Agreement
acknowledge that OLP is borrowing the OLP Debt concurrently herewith.

     Section 2.11 DISTRIBUTION OF CASH BY OLP TO MLP. OLP hereby distributes to
MLP, its successors and assigns, for its and their own use forever, a portion of
the proceeds from the OLP Debt, equal to $26,700,000, and MLP accepts such funds
as a distribution.

     Section 2.12 DISTRIBUTION OF CASH BY MLP TO GP. MLP hereby distributes to
GP, its successors and assigns, for its and their use forever, a portion of the
funds received from OLP, equal to $26,300,000, and GP accepts such proceeds as a
distribution and in reimbursement of $6,200,000 of capital expenditures.

     Section 2.13 DISTRIBUTION OF CASH BY MLP TO MICHIGAN. MLP hereby
distributes to Michigan, its successors and assigns, for its and their use
forever, a portion of the funds received from OLP equal to $400,000 and Michigan
accepts such funds in reimbursement of $400,000 of capital expenditures.

     Section 2.14 DISTRIBUTION OF GP'S SUB UNITS AND CASH TO MARKWEST. GP hereby
distributes to MarkWest, its successors and assigns, for its and their use
forever, GP's Sub Units and a portion of the funds received from MLP equal to
$36,200,000, and MarkWest accepts such Sub Units and proceeds as a distribution.

     Section 2.15 SALE OF SUB UNITS BY MARKWEST TO THE MANAGEMENT GROUP. The
parties to this Agreement acknowledge the 24,864 Sub Units to the Management
Group for $397,824.

     Section 2.16 SALE OF INTEREST IN GP BY MARKWEST TO THE MANAGEMENT GROUP.
The parties to this Agreement acknowledge the sale by MarkWest of an
8.6%membership interest in GP to the Management Group for $175,000.

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                                   ARTICLE 3
                             ADDITIONAL TRANSACTIONS

     Section 3.1 PURCHASE OF ADDITIONAL COMMON UNITS. IF THE OPTION IS EXERCISED
IN WHOLE OR IN PART, THE PUBLIC, THROUGH THE UNDERWRITERS, WILL CONTRIBUTE
ADDITIONAL CASH TO MLP IN EXCHANGE FOR UP TO AN ADDITIONAL 300,000 COMMON UNITS,
AND THE NET PROCEEDS THEREOF WILL BE USED TO RETIRE A PORTION OF THE OLP DEBT AS
A PARTIAL REIMBURSEMENT FOR CAPITAL EXPENDITURES INCURRED BY MARKWEST.

                                   ARTICLE 4
                        ASSUMPTION OF CERTAIN LIABILITIES

     Section 4.1 ASSUMPTION OF THE MARKWEST LIABILITIES BY MEA. In connection
with MarkWest's contribution and transfer of the Assets to MEA, MEA hereby
assumes and agrees to duly and timely pay, perform and discharge the MarkWest
Liabilities, to the full extent that MarkWest has been heretofore or would have
been in the future, were it not for the execution and delivery of this
Agreement, obligated to pay, perform and discharge the MarkWest Liabilities;
provided, however, that said assumption and agreement to duly and timely pay,
perform and discharge the MarkWest Liabilities shall not increase the obligation
of MEA with respect to the MarkWest Liabilities beyond that of MarkWest, waive
any valid defense that was available to MarkWest with respect to the MarkWest
Liabilities or enlarge any rights or remedies of any third party, if any, under
any of the MarkWest Liabilities. This assumption shall inure to the benefit of
MarkWest, its shareholders, officers, directors, employees and agents.

     Section 4.2 ASSUMPTION OF THE MICHIGAN LIABILITIES BY MLP. In connection
with Michigan's contribution and transfer of the Basin Interest and West Shore
Interest to MLP, MLP hereby assumes and agrees to duly and timely pay, perform
and discharge the Michigan Liabilities, to the full extent that Michigan has
been heretofore or would have been in the future, were it not for the execution
and delivery of this Agreement, obligated to pay, perform and discharge the
Michigan Liabilities; provided, however, that said assumption and agreement to
duly and timely pay and discharge the Michigan Liabilities shall not increase
the obligation of MLP with respect to the Michigan Liabilities beyond that of
Michigan, waive any valid defense that was available to Michigan with respect to
the Michigan Liabilities or enlarge any rights or remedies of any third party,
if any, under any of the Michigan Liabilities. This assumption shall inure to
the benefit of Michigan, its members and each of their predecessors-in-interest
and each of their shareholders, officers, directors, employees and agents.

                                   ARTICLE 5
                                 INDEMNIFICATION

     Section 5.1 INDEMNIFICATION WITH RESPECT TO EXCLUDED LIABILITIES. MarkWest
shall indemnify, defend and hold harmless GP, OLP, MLP and their respective
successors and assigns from and against all Claims arising from or relating to
the Excluded Liabilities; provided, however, MarkWest's indemnity obligation
shall only apply with respect to Claims as to which it received written notice
from GP, OLP or MLP within one year following the date hereof.

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     Section 5.2 INDEMNIFICATION BY OLP WITH RESPECT TO OPERATION OF THE
BUSINESS AND THE ASSUMED LIABILITIES. The OLP shall indemnify, defend and hold
harmless MarkWest, Michigan, GP and MLP and their respective successors and
assigns from and against any and all Claims (including, without limitation,
costs of environmental investigation and remediation and penalties and other
assessments) arising from or relating to the Assumed Liabilities, or the
operation of the Assets or the Business, excluding any claims, demands, costs,
liabilities and expenses arising from or relating to the Excluded Liabilities
for which written notice was provided to MarkWest within one year following the
date hereof, provided, however, that notwithstanding the foregoing, OLP shall
not be required to indemnify, defend and hold harmless MarkWest and its
successors and assigns to the extent that any of the foregoing claims, demands,
costs, liabilities and expenses are recovered through insurance proceeds paid to
MarkWest.

     Section 5.3 INDEMNIFICATION BY MLP WITH RESPECT TO OPERATION OF THE
BUSINESS AND THE ASSUMED LIABILITIES. The MLP shall indemnify, defend and hold
harmless MarkWest, Michigan and GP and their respective successors and assigns
from and against any and all Claims (including, without limitation, costs of
environmental investigation and remediation and penalties and other assessments)
arising from or relating to the Assumed Liabilities, or the operation of the
Assets or the Business, excluding any claims, demands, costs, liabilities and
expenses arising from or relating to the Excluded Liabilities for which written
notice was provided to MarkWest within one year following the date hereof,
provided, however, that notwithstanding the foregoing, MLP shall not be required
to indemnify, defend and hold harmless MarkWest and its successors and assigns
to the extent that any of the foregoing claims, demands, costs, liabilities and
expenses are recovered through insurance proceeds paid to MarkWest.

     Section 5.4 INDEMNIFICATION BY GP WITH RESPECT TO OPERATION OF THE BUSINESS
AND THE ASSUMED LIABILITIES. The GP shall indemnify, defend and hold harmless
MarkWest and its respective successors and assigns from and against any and all
Claims (including, without limitation, costs of environmental investigation and
remediation and penalties and other assessments) arising from or relating to the
Assumed Liabilities, or the operation of the Assets or the Business, excluding
any claims, demands, costs, liabilities and expenses arising from or relating to
the Excluded Liabilities for which written notice was provided to MarkWest
within one year following the date hereof, provided, however, that
notwithstanding the foregoing, GP shall not be required to indemnify, defend and
hold harmless MarkWest and its successors and assigns to the extent that any of
the foregoing claims, demands, costs, liabilities and expenses are recovered
through insurance proceeds paid to MarkWest.

     Section 5.5 COVERED ENVIRONMENTAL LOSSES. Nothing herein is intended to
affect or apply to Covered Environmental Losses, as such are defined in the
Omnibus Agreement, and which shall be governed by the Omnibus Agreement.

                                   ARTICLE 6
                                  TITLE MATTERS

     Section 6.1 ENCUMBRANCES. The contribution of the Assets made under Section
2.1 is made expressly subject to all recorded and unrecorded liens,
encumbrances, agreements, defects,

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restrictions, adverse claims and all laws, rules, regulations, ordinances,
judgments and orders of governmental authorities or tribunals having or
asserting jurisdiction over the Assets or the Business and operations conducted
thereon or therewith, in each case to the extent the same are valid, enforceable
and affect the Assets, including, without limitation, all matters that a current
survey or visual inspection of the Assets would reflect.

     Section 6.2 DISCLAIMER OF WARRANTIES; SUBROGATION; WAIVER OF BULK SALES
LAWS.

          (a) NOTWITHSTANDING ANYTHING TO THE CONTRARY CONTAINED IN THIS
AGREEMENT, MARKWEST AND MEA ACKNOWLEDGE AND AGREE MARKWEST HAS NOT MADE, DOES
NOT MAKE AND SPECIFICALLY NEGATES AND DISCLAIMS, ANY REPRESENTATIONS,
WARRANTIES, PROMISES, COVENANTS, AGREEMENTS OR GUARANTIES OF ANY KIND OR
CHARACTER WHATSOEVER, WHETHER EXPRESS, IMPLIED OR STATUTORY, ORAL OR WRITTEN,
PAST OR PRESENT (ALL OF WHICH ARE EXPRESSLY DISCLAIMED BY MARKWEST REGARDING
(1) THE TITLE, VALUE, NATURE, QUALITY OR CONDITION OF THE ASSETS, INCLUDING,
WITHOUT LIMITATION, THE WATER, SOIL, GEOLOGY OR ENVIRONMENTAL CONDITION OF THE
ASSETS GENERALLY, INCLUDING THE PRESENCE OR LACK OF HAZARDOUS SUBSTANCES OR
OTHER MATTERS ON THE ASSETS, (2) THE INCOME TO BE DERIVED FROM THE ASSETS, (3)
THE SUITABILITY OF THE ASSETS FOR ANY AND ALL ACTIVITIES AND USES WHICH MEA MAY
CONDUCT THEREON, (4) THE COMPLIANCE OF OR BY THE ASSETS OR THEIR OPERATIONS
WITH ANY LAWS (INCLUDING WITHOUT LIMITATION ANY ZONING, ENVIRONMENTAL
PROTECTION, POLLUTION OR LAND USE LAWS, RULES, REGULATIONS, ORDERS OR
REQUIREMENTS), OR (5) THE HABITABILITY, MERCHANTABILITY, MARKETABILITY,
PROFITABILITY OR FITNESS FOR A PARTICULAR PURPOSE OF THE ASSETS. MARKWEST AND
MEA ACKNOWLEDGE AND AGREE MEA HAS HAD THE OPPORTUNITY TO INSPECT THE ASSETS AND
MEA IS RELYING SOLELY ON ITS OWN INVESTIGATION OF THE ASSETS, AND NOT ON ANY
INFORMATION PROVIDED OR TO BE PROVIDED BY MARKWEST AND MARKWEST IS NOT LIABLE OR
BOUND IN ANY MANNER BY ANY VERBAL OR WRITTEN STATEMENTS, REPRESENTATIONS OR
INFORMATION PERTAINING TO THE ASSETS FURNISHED BY ANY AGENT, EMPLOYEE, SERVANT
OR THIRD PARTY. MARKWEST AND MEA EACH ACKNOWLEDGE THAT TO THE MAXIMUM EXTENT
PERMITTED BY LAW, THE CONTRIBUTION OF THE ASSETS AS PROVIDED FOR HEREIN IS MADE
ON AN "AS IS", "WHERE IS" BASIS WITH ALL FAULTS AND THE ASSETS ARE CONTRIBUTED
OR DISTRIBUTED AND CONVEYED BY MARKWEST AND ACCEPTED BY MEA SUBJECT TO THE
FOREGOING. THIS PARAGRAPH SHALL SURVIVE SUCH CONTRIBUTION OR DISTRIBUTION AND
CONVEYANCE OR THE TERMINATION OF THIS AGREEMENT. THE PROVISIONS OF THIS SECTION
6.2(a) HAVE BEEN NEGOTIATED BY MARKWEST AND MEA AFTER DUE CONSIDERATION AND ARE
INTENDED TO BE A COMPLETE EXCLUSION AND NEGATION OF ANY REPRESENTATIONS OR
WARRANTIES OF MARKWEST, WHETHER EXPRESS, IMPLIED OR STATUTORY, WITH RESPECT TO
THE ASSETS THAT MAY ARISE PURSUANT TO ANY LAW NOW OR HEREAFTER IN EFFECT, OR
OTHERWISE.

                                       11
<Page>

          (b) The contribution of the Assets made under Section 2.1 is made with
full rights of substitution and subrogation of MEA, and all persons claiming by,
through and under MEA, to the extent assignable, in and to all covenants and
warranties by the predecessors-in-title of MarkWest, and with full subrogation
of all rights accruing under applicable statutes of limitation and all rights of
action of warranty against all former owners of the Assets.

          (c) MarkWest and MEA agree that the disclaimers contained in this
Section 6.2 are conspicuous disclaimers. Any covenants implied by statute or law
by the use of the words grant, convey, bargain, sell, assign, transfer, deliver
or set over, or any of them or any other words used in this Agreement, are
hereby expressly disclaimed, waived and negated.

          (d) Each of the parties hereto hereby waives compliance with any
applicable bulk sales law or any similar law in any applicable jurisdiction in
respect of the transactions contemplated by this Agreement.

                                   ARTICLE 7
                               FURTHER ASSURANCES

     Section 7.1 MARKWEST ASSURANCES. From time to time after the Effective
Time, and without any further consideration, MarkWest shall execute, acknowledge
and deliver all such additional deeds, assignments, conveyances, instruments,
notices, releases, acquittances and other documents, and will do all such other
acts and things, including any required conveyance of certificated titles or
other official registration documentation, all in accordance with applicable
law, as may be necessary or appropriate (a) to more fully assign to MEA, and
each of its successors and assigns, all of the properties, rights, titles,
interests, estates, remedies, powers and privileges by this Agreement granted to
MEA or intended so to be, and (b) to more fully and effectively carry out the
purposes and intent of this Agreement. Additionally, from time to time after the
Effective Time, and without any further consideration, MarkWest will do all acts
necessary or appropriate to assign to MEA any rights to indemnification
associated with the Assets, to the extent assignable, or if not assignable, do
all acts necessary or appropriate to assign to MEA the benefits of any such
rights, including, without limitation, filing claims for indemnification and
pursuing such claims in good faith and with diligence until completion.

     Section 7.2 OTHER ASSURANCES. From time to time after the Effective Time,
and without any further consideration, MarkWest, GP, Michigan and MLP shall
execute, acknowledge and deliver all such additional instruments, notices and
other documents, and will do all such other acts and things, all in accordance
with applicable law, as may be necessary or appropriate to more fully and
effectively carry out the purposes and intent of this Agreement.

                                   ARTICLE 8
                                 EFFECTIVE TIME

     Notwithstanding anything contained in this Agreement to the contrary, none
of the provisions of Article 2, Article 3, Article 4 or Article 5 of this
Agreement shall be operative or have any effect until the Effective Time, at
which time all the provisions of Article 2, Article 3, Article 4 and Article 5
of this Agreement shall be effective and operative as of the Effective Time,
without further action by any party hereto.

                                       12
<Page>

                                   ARTICLE 9
                                  MISCELLANEOUS

     Section 9.1 ORDER OF COMPLETION OF TRANSACTIONS. The transactions provided
for in Article 2 and Article 3 of this Agreement shall be completed immediately
following the Effective Time in the following order: first, the transactions
provided for in Article 2 shall be completed; and second, following the
completion of the transactions as provided in Article 2, the transactions, if
they occur, provided for in Article 3 shall be completed.

     Section 9.2 CONSENTS; RESTRICTION ON ASSIGNMENT. If there are prohibitions
against or conditions to the conveyance of one or more portions of the Assets
without the prior written consent of third parties, including, without
limitation, governmental agencies (other than consents of a ministerial nature
which are normally granted in the ordinary course of business), which if not
satisfied would result in a breach of such prohibitions or conditions or would
give an outside party the right to terminate MEA's rights with respect to such
portion of the Assets (a "RESTRICTION"), then any provision contained in this
Agreement to the contrary notwithstanding, the transfer of title to or interest
in each such portion of the Assets (the "RESTRICTION-ASSET") pursuant to this
Agreement shall not become effective unless and until such Restriction is
satisfied, waived or no longer applies. When and if such a Restriction is so
satisfied, waived or no longer applies, to the extent permitted by applicable
law and any applicable contractual provisions, the assignment of the
Restriction-Asset subject thereto shall become effective automatically as of the
date of this Agreement, without further action on the part of MEA or MarkWest.
MarkWest and OLP agree to use their best efforts to obtain satisfaction of any
Restriction on a timely basis. The description of any portion of the Assets as a
Restriction-Asset shall not be construed as an admission that any Restriction
exists with respect to the transfer of such portion of the Assets. In the event
that any Restriction-Asset exists, MarkWest agrees to hold such
Restriction-Asset in trust for the exclusive benefit of MEA and to otherwise use
its best efforts to provide OLP with the benefits thereof, and MarkWest will
enter into other agreements, or take such other action as it deems necessary, in
order to help ensure that OLP has all of the Assets and concomitant rights
necessary to operate the Business.

     Section 9.3 COSTS. The OLP shall pay all expenses, fees and costs,
including but not limited to, all sales, use and similar taxes, arising out of
the contributions, conveyances and deliveries to be made hereunder and shall pay
all documentary, filing, recording, transfer, deed, and conveyance taxes and
fees required in connection therewith. In addition, the OLP shall be responsible
for all costs, liabilities and expenses (including court costs and reasonable
attorneys' fees) incurred in connection with the implementation of any
conveyance or delivery pursuant to Section 7.1 or Section 7.2 or the
satisfaction or waiver of any Restriction pursuant to Section 9.2.

     Section 9.4 HEADINGS; REFERENCES; INTERPRETATION. All Article and Section
headings in this Agreement are for convenience only and shall not be deemed to
control or affect the meaning or construction of any of the provisions hereof.
The words "hereof," "herein" and "hereunder" and words of similar import, when
used in this Agreement, shall refer to this Agreement as a whole, including,
without limitation, all Schedules and Exhibits attached hereto, and not to any
particular provision of this Agreement. All references herein to Articles,
Sections, Schedules and Exhibits shall, unless the context requires a different
construction, be deemed to

                                       13
<Page>

be references to the Articles and Sections of this Agreement and the Schedules
and Exhibits attached hereto, and all such Schedules and Exhibits attached
hereto are hereby incorporated herein and made a part hereof for all purposes.
All personal pronouns used in this Agreement, whether used in the masculine,
feminine or neuter gender, shall include all other genders, and the singular
shall include the plural and vice versa. The use herein of the word including
following any general statement, term or matter shall not be construed to limit
such statement, term or matter to the specific items or matters set forth
immediately following such word or to similar items or matters, whether or not
non-limiting language (such as without limitation, but not limited to, or words
of similar import) is used with reference thereto, but rather shall be deemed to
refer to all other items or matters that could reasonably fall within the
broadest possible scope of such general statement, term or matter.

     Section 9.5 SUCCESSORS AND ASSIGNS. The Agreement shall be binding upon and
inure to the benefit of the parties signatory hereto and their respective
successors and assigns.

     Section 9.6 NO THIRD PARTY RIGHTS. The provisions of this Agreement are
intended to bind the parties signatory hereto as to each other and are not
intended to and do not create rights in any other person or confer upon any
other person any benefits, rights or remedies and no person is or is intended to
be a third party beneficiary of any of the provisions of this Agreement.

     Section 9.7 COUNTERPARTS. This Agreement may be executed in any number of
counterparts, all of which together shall constitute one agreement binding on
the parties hereto.

     Section 9.8 GOVERNING LAW. This Agreement shall be governed by, and
construed in accordance with, the laws of the state of Colorado applicable to
contracts made and to be performed wholly within such state without giving
effect to conflict of law principles thereof, except to the extent that it is
mandatory that the law of a jurisdiction wherein an Asset is located shall
apply.

     Section 9.9 SEVERABILITY. If any of the provisions of this Agreement are
held by any court of competent jurisdiction to contravene, or to be invalid
under, the laws of any political body having jurisdiction over the subject
matter hereof, such contravention or invalidity shall not invalidate the entire
Agreement. Instead, this Agreement shall be construed as if it did not contain
the particular provision or provisions held to be invalid and an equitable
adjustment shall be made and necessary provision added so as to give effect to
the intention of the parties as expressed in this Agreement at the time of
execution of this Agreement.

     Section 9.10 DEED; BILL OF SALE; ASSIGNMENT. To the extent required by
applicable law, this Agreement shall, as of the Effective Time, also constitute
a deed, bill of sale or assignment of the Assets.

     Section 9.11 AMENDMENT OR MODIFICATION. This Agreement may be amended or
modified from time to time only by the written agreement of all the parties
hereto. Each such instrument shall be reduced to writing and shall be designated
on its face as an Amendment to this Agreement.

                                       14
<Page>

     Section 9.12 INTEGRATION. This Agreement supersedes all previous
understandings or agreements between the parties, whether oral or written, with
respect to its subject matter. This document is an integrated agreement which
contains the entire understanding of the parties. No understanding,
representation, promise or agreement, whether oral or written, is intended to be
or shall be included in or form part of this Agreement unless it is contained in
a written amendment hereto executed by the parties hereto after the date of this
Agreement.

            [THE REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK]

                                       15
<Page>

     IN WITNESS WHEREOF, this Agreement has been duly executed by the parties
hereto as of the date first above written.

MARKWEST ENERGY OPERATING               MARKWEST ENERGY APPALACHIA, L.L.C.
COMPANY, L.L.C.

By: MarkWest Energy Partners, L.P.,     By: MarkWest Hydrocarbon, Inc., its
    its sole member                         sole member

    By: MarkWest Energy GP, L.L.C.,
        its General Partner

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

MARKWEST MICHIGAN, INC.                 MARKWEST ENERGY PARTNERS, L.P.
                                        By: MarkWest Energy GP, L.L.C., its
                                            General Partner

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

MARKWEST HYDROCARBON, INC.              MARKWEST ENERGY GP, L.L.C.
                                        By: MarkWest Hydrocarbon, Inc., its
                                            sole member

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

WEST SHORE PROCESSING COMPANY, L.L.C.
By: MarkWest Michigan, Inc., its Manager

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

                                       16
<Page>

                                   EXHIBIT A

                                     Assets

                                      A-1

<Page>

                                   EXHIBIT B-1

                                     [Deeds]

                                      B-1

<Page>

                                   EXHIBIT B-2

                                 [Bills of Sale]

                                      B-2
<Page>

                                   EXHIBIT C

                                Management Group

NAME & ADDRESS

JOHN M. FOX
[Address]
[Phone & Fax]

ARTHUR J. DENNEY
[Address]
[Phone & Fax]

GERALD TYWONIUK
[Address]
[Phone & Fax]

RANDY S. NICKERSON
[Address]
[Phone & Fax]

JOHN C. MOLLENKOPF
[Address]
[Phone & Fax]

FREDERICK J. WITSELL
[Address]
[Phone & Fax]

GRANT M. CARNIE
[Address]
[Phone & Fax]

                                      C-1<Page>

                  FRACTIONATION, STORAGE AND LOADING AGREEMENT
                                    (Siloam)

     This Fractionation, Storage and Loading Agreement ("Agreement") is made and
entered into this ____ day of ______, 2002, by and between MARKWEST ENERGY
APPALACHIA, L.L.C., a Delaware limited partnership ("MEA"), and MARKWEST
HYDROCARBON, INC., a Delaware corporation ("MarkWest"). MEA and MarkWest may be
referred to individually as "Party", or collectively as "Parties".

     Section 1. SCOPE OF AGREEMENT AND GENERAL TERMS AND CONDITIONS. MarkWest
agrees to deliver, or cause to be delivered, Raw Make, as defined below, to MEA,
and MEA agrees to receive and fractionate that Raw Make into Plant Products, as
defined below, and to store, load and deliver Plant Products to MarkWest, all in
accordance with this Agreement. This Agreement incorporates and is subject to
all of the General Terms and Conditions attached hereto, together with any other
Exhibits attached hereto.

     Section 2. EFFECTIVE DATE. The date on which the obligations and duties of
the Parties shall commence, being the "Effective Date", shall be
_______________, 2002.

     Section 3. TERM. This Agreement shall remain in full force and effect from
the Effective Date for a period of 10 years (the "Primary Term"), and shall
continue thereafter on a year-to-year basis until terminated by either Party by
providing at least 60 days written notice to the other Party in advance of the
termination of the Primary Term or of any one-year extension thereof.

     Section 4. FEES AND CONSIDERATION.

     A.   As full consideration for the services provided by MEA, MarkWest shall
     pay the following fees and MEA shall make the following deliveries:

          i.   For the fractionation of Raw Make into Plant Products, by MEA, at
          Siloam, MarkWest shall pay MEA a Fractionation Fee equal to the
          gallons of Raw Make fractionated multiplied by $*. The Fractionation
          Fee covers, and is inclusive of the MEA's costs for fractionating Raw
          Make, loading Plant Products and above ground storage of Plant
          Products.

          ii.  For the exclusive use of the Cavern, MarkWest shall pay MEA an
          Annual Storage Fee equal to $* for MEA storing MarkWest's Plant
          Products in the Cavern.

          iii. Should MarkWest deliver any Raw Make to Siloam by railcar, MEA
          shall unload the Raw Make for fractionation and MarkWest shall pay MEA
          an Unloading Fee of $* per gallon of Raw Make unloaded from railcars.

          iv.  A portion of each of the Fractionation Fee, Annual Storage Fee
          and Unloading Fee (collectively, the "Fees") shall be subject to
          annual adjustments. *% of each of the Fees, shall be adjusted on an
          annual basis in proportion to the percentage change, from the
          preceding year, in the Producer Price Index for oil and gas field
          services (SIC 138) as published by the Department of Labor

                    *Denotes Confidential Portion Omitted and
                      Filed Separately with the Commission

                                       1

<Page>

          ("PPI"). The adjustment of the Fees shall be made effective January 1
          of each year, and shall reflect the percentage change in the PPI as it
          existed for the immediately preceding January from the PPI for the
          second immediately preceding January.

          v.   MEA shall deliver and load the Plant Products fractionated from
          MarkWest's Raw Make to the Product Delivery Points in accordance with
          the terms of this Agreement.

     Section 5. NOTICES. All notices, statements, invoices or other
communications required or permitted between the Parties shall be in writing and
shall be considered as having been given if delivered by mail, courier, hand
delivery, or facsimile to the other Party at the designated address or facsimile
numbers. Normal operating instructions can be delivered by telephone or other
agreed means. Notice of events of Force Majeure may be made by telephone and
confirmed in writing within a reasonable time after the telephonic notice.
Monthly statements, invoices, payments and other communications shall be deemed
delivered when actually received. Either Party may change its address or
facsimile and telephone numbers upon written notice to the other Party:

     MarkWest:

          Address:  155 Inverness Drive West, Suite 200
                    Englewood, Colorado 80112
                    Attn: Contract Administration
                    Fax: (303) 290-8769

     MEA:

          Address:  155 Inverness Drive West, Suite 200
                    Englewood, Colorado 80112
                    Attn: Contract Administration
                    Fax: (303) 290-8769

     Section 6. EXECUTION. This Agreement may be executed in any number of
counterparts, each of which shall be considered and original, and all of which
shall be considered one instrument.

IN WITNESS WHEREOF, the Parties have executed this Agreement on the date first
set forth above.

                                        MARKWEST HYDROCARBON, INC.

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

                                        MARKWEST ENERGY APPALACHIA, L.L.C.

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

                                       2
<Page>

                          GENERAL TERMS AND CONDITIONS
                   ATTACHED TO AND MADE A PART OF THAT CERTAIN
                  FRACTIONATION, STORAGE AND LOADING AGREEMENT
                                     BETWEEN
                    MARKWEST HYDROCARBON, INC., AS "MARKWEST"
                                       AND
                  MARKWEST ENERGY APPALACHIA, L.L.C., AS "MEA"
                                     DATED:

ARTICLE 1: DEFINITIONS

ACCOUNTING PERIOD. The period commencing at 10:00 a.m., Eastern Time, on the
first day of a calendar month and ending at 10:00 a.m., Eastern Time, on the
first day of the next succeeding month.

CAVERN. The two underground Plant Products storage cavern owned and operated by
MEA at Siloam with a capacity of approximately 11,000,000 gallons.

FORCE MAJEURE. Any cause or condition not within the reasonable control of the
Party claiming suspension and which by the exercise of reasonable diligence,
such Party is unable to prevent or overcome.

FRACTIONATION FUEL. All Gas, Plant Products, vapors or other forms of energy
utilized as fuel in Siloam.

GAS. All hydrocarbon and non-hydrocarbon substances in a gaseous state.

INCIDENTAL LOSSES OR GAINS. The incidental losses of Raw Make and/or Plant
Products incurred in MEA's facilities, or the losses or gains of Raw Make and/or
Plant Products incurred due to variations in measurement equipment.

INDEMNIFYING PARTY and INDEMNIFIED PARTY. As defined in Article 8, below.

LOSSES. Any actual loss, cost, expense, liability, damage, demand, suit,
sanction, claim, judgment, lien, fine or penalty which are incurred by the
applicable Indemnified Party on account of injuries (including death) to any
person or damage to or destruction of any property, sustained or alleged to have
been sustained in connection with or arising out of the matters for which the
Indemnifying Party has indemnified the applicable Indemnified Party.

MEA PLANTS. Gas processing and extraction plants, owned and/or operated by MEA.

PLANT PRODUCTS. The finished liquid products fractionated from the Raw Make
delivered hereunder, including propane (including incidental ethane), isobutane,
normal butane and natural gasoline.

PLANT PRODUCTS DELIVERY POINT. The point at which the Plant Products are
delivered to, or for the account of, MarkWest into transportation facilities
furnished by MarkWest.

RAW MAKE. A combined stream of propane and heavier liquefied hydrocarbons,
including incidental ethane.

RECEIPT POINT. For Raw Make, the inlet flange of the pipeline at the point at
which MarkWest delivers Raw Make into the pipeline, and for Raw Make delivered
by truck trailer or by tank car, the inlet flange of the Raw Make unloading
facilities of MEA at or near Siloam.

SILOAM. MEA's Siloam fractionation facility located near South Shore, Kentucky,
including any treating equipment, Plant Products separation and fractionation

                        1 of General Terms and Conditions
<Page>

vessels, all above ground Plant Products storage vessels and all below ground
Plant Products and Raw Make storage caverns and facilities, and associated
condensing, heating, pumping, conveying, and other equipment and
instrumentation; including all structures associated with those facilities; and,
all Plant Products loading facilities, including railcar loading, truck loading
and barge loading facilities and including all easements, rights-of-way, and
other property rights pertaining to the construction and operation of those
facilities; wherever those facilities, structures, easements, rights-of-way, and
other property rights are located.

ARTICLE 2: MARKWEST COMMITMENTS

2.1. MarkWest hereby commits and agrees to deliver at the Receipt Points all of
MarkWest's Raw Make acquired from the MEA Plants, or from other extraction
plants in the Appalachian region, unless there is not sufficient available
capacity at Siloam to fractionate any portion thereof, in which case MarkWest
shall not be obligated to deliver the portion for which there is no capacity.

ARTICLE 3: OPERATION OF MEA'S FACILITIES

3.1. Subject to the other provisions of this Agreement, MEA agrees to accept all
of MarkWest's Raw Make, up to the capacity of Siloam, fractionate the Raw Make
into Plant Products in accordance with this Agreement and to store and load
Plant Products for MarkWest as provided herein.

3.2  MEA agrees that it shall, at its sole cost, risk, and expense, furnish all
Fractionation Fuel for operating Siloam, and in no event shall any of MarkWest's
Raw Make delivered hereunder or Plant Products or any vapors therefrom be
consumed or utilized by MEA as Fractionation Fuel or in any other manner prior
to delivery of Plant Products to MarkWest as herein provided.

3.3  MEA agrees that it shall, at its sole cost, risk, and expense, operate,
maintain, and replace (if necessary) docks, loading racks, pipelines, and all
other facilities for loading each Product for shipment by highway, rail, and
marine transportation from the vicinity of Siloam. MEA agrees that all
facilities operated by MEA which are required in the performance of the services
herein agreed upon shall, at its sole cost, risk, and expense, be maintained and
operated at all times as a prudent operator would maintain and operate similar
facilities. MEA hereby grants MarkWest, at no additional consideration, the
trackage rights on MEA's Siloam railroad siding to move Product hereunder.

3.4. MEA agrees that it shall, at its sole cost, risk, and expense, be
responsible for all loading of each Product for shipments in accordance with
reasonable authorizations and instructions given from time to time by MarkWest,
including, but not limited to, preparation and distribution of all shipping
papers pertaining to movement of Plant Products from Siloam, rail, truck and
barge bills of lading, loading tickets, and reports and odorization
certifications. MEA shall furnish all trained employees required to perform
these services and shall maintain complete records of all Product dispositions.

3.5. MEA agrees that it shall, at its sole risk, be responsible for placing
Plant Products into storage in the Cavern and withdrawing Plant Products from
the Cavern in accordance with reasonable authorizations and instructions given
from time to time by MarkWest.

3.6  All Incidental Losses and Gains incurred at Siloam shall be allocated to
MarkWest and other parties for whom MEA is fractionating Raw Make at Siloam.

ARTICLE 4: QUALITY

4.1. RAW MAKE QUALITY.

                        2 of General Terms and Conditions
<Page>

A.   The Raw Make fractionated under this Agreement is derived from MEA Plants,
and from other plants. As long as the Raw Make delivered hereunder for
fractionation is of a quality which, when fractionated, meets the applicable
specifications set forth on Exhibit A, attached hereto, then MEA agrees to
receive and fractionate that Raw Make into Plant Products meeting the
specifications set forth herein.

B.   Should any of the Raw Make fail to meet the above specifications, then:

     i.   MEA may take receipt of the non-conforming Raw Make, and that receipt
     shall not be construed as a waiver or change of standards for future Raw
     Make deliveries; or

     ii.  MEA may, at its sole discretion, cease receiving the non-conforming
     Raw Make, and shall notify MarkWest that it has, or will, cease receiving
     the non-conforming Raw Make.

4.2  PLANT PRODUCTS QUALITY. MEA shall fractionate all Raw Make meeting the
requirements under Section 4.1, to produce Plant Products meeting the
specifications set forth on Exhibit A, attached hereto.

4.3  MEA shall odorize Plant Products in accordance with the directions of
MarkWest.

ARTICLE 5: MEASUREMENT EQUIPMENT AND PROCEDURES AND ANALYSES

5.1. RAW MAKE. Raw Make shall be measured at the respective Receipt Point(s) and
shall conform to applicable API and GPA standards for pipeline, truck, and rail
car measurement as follows:

     (1)  For Raw Make delivered by pipeline:

     A.   MEA shall measure the weight of the Raw Make delivered hereunder using
     either turbine or coriolis mass flow meters installed, operated and
     maintained in accordance with GPA Standard 8182-latest edition and/or API
     Manual of Petroleum Measurement Standards Draft Standard, Measurement of
     Single-Phase, Intermediate and Finished Hydrocarbon Fluids by Coriolis
     Meters-latest edition.

     B.   MEA shall measure the composition of the Raw Make delivered hereunder
     using a chromatograph installed, operated and maintained in accordance with
     GPA Standard 2165-latest edition, GPA Standard 2145-latest edition, GPA
     Standard 2261-latest edition, GPA Standard 2177-latest edition and the
     manufacturer's specifications and standards. Factors for hexanes and
     heavier shall be in accordance with Table IV of GPA Standard 2261-latest
     edition or determined by periodic samples taken by the MEA. Samples shall
     be taken at intervals not to exceed 20 minutes. The arithmetic average of
     the samples during a day shall be deemed to be the Raw Make Composition for
     such day.

     C.   The weight of each Raw Make component shall be converted to gallons at
     60(degree)F in accordance with GPA Standard 8173-latest edition and GPA
     Standard 2145-latest edition.

     (2)  The trucks shall be weighed empty and full. GPA Standard 8186, as
revised, is the standard to be used on all truck deliveries.

     (3)  Rail cars shall be measured using strapping tables and liquid spew
gauges. Vapor correction calculations will be made as required by applicable
industry standards.

5.2 PLANT PRODUCTS MEASUREMENT.

                        3 of General Terms and Conditions
<Page>

Measurement of all Plant Products and deliveries shall be converted to 60oF and
shall conform to applicable API and GPA standards for barge, truck, and rail car
measurement:

     (1)  Barge loading will be by strapping tables. Vapor correction will be
included on delivery tickets on all Plant Products except gasoline.

     (2)  The trucks shall be weighed empty and full. GPA Standard 8186, as
revised, is the standard to be used on all truck deliveries.

     (3)  Rail cars shall be measured using strapping tables and liquid spew
gauges. Vapor correction calculations will be made as required by applicable
industry standards.

5.3  If any measuring equipment used herein is out of service or, upon test, is
found to be in error by an amount exceeding 1%, at a recording rate
corresponding to the average rate of flow for the period since the last
preceding test, then any preceding recordings of that equipment since the last
preceding test shall be corrected to zero error for any period which is known
definitely or agreed upon. If the period is not known definitely or agreed upon,
the correction shall be for a period extending back one-half of the time elapsed
since the last test. In the event a correction is required for previous
deliveries, the volumes delivered shall be calculated by the first of the
following methods which is feasible: (i) by using the registration of any check
meter or meters if installed and accurately registering; or (ii) by correcting
the error if the percentage of error is ascertainable by calibration, test, or
mathematical calculations; or (iii) by MarkWest estimating the quantity of
delivery by deliveries during periods of similar conditions when the meter was
registering accurately.

5.4  INVENTORY.

A.   MEA will maintain and provide MarkWest with daily reports setting forth the
volumes of MarkWest's Raw Make and Plant Products held in inventory at Siloam.

B.   MEA shall measure the inventory of each above ground storage tank using
tank gauges and shall measure the inventory in the Cavern using inlet and outlet
meters and gauges. Such meters and gauges shall be installed, operated and
maintained in accordance with applicable industry standards.

C.   At MarkWest's request, MEA shall operate the Cavern(s) in either propane or
butane service; provided, that MarkWest pays MEA in advance for all reasonable
and necessary costs to convert from one service to the other.

5.5  ANALYSES.

A.   MEA shall, at its sole cost, risk, and expense, install, operate, and
maintain equipment to analyze the composition of the Raw Make and of the Plant
Products in accordance with applicable GPA standards.

B.   With respect to Raw Make delivered by tank and truck cars, and with respect
to Plant Products, samples shall be analyzed in accordance with applicable GPA
standards. The analysis shall also include the determination of the molecular
weight, density, and heating value of the hexane and heavier fraction be
extended analysis, quarterly in accordance with industry recognized standards.
MarkWest or MEA or their representatives may take samples for verification of
composition and may be present during any of the other party's sampling
operations.

ARTICLE 6: PAYMENTS

6.1. MEA shall provide MarkWest with a statement explaining fully how all

                        4 of General Terms and Conditions
<Page>

consideration due under the terms of this Agreement was determined not later
than the 20th day of the Accounting Period following the Accounting Period for
which the consideration is due.

6.2. Any sums due MEA under this Agreement shall be paid no later than the last
day of the Accounting Period in which the statement provided under Section 6.1
was received.

6.3. Either Party, on 10 days prior written notice, shall have the right at its
expense, at reasonable times during business hours, to audit the books and
records of the other Party to the extent necessary to verify the accuracy of any
statement, measurement, computation, charge, or payment made under or pursuant
to this Agreement. A Party electing to audit ("Auditing Party") shall complete
its audit within 3 months following the date on which the books and records of
the other Party ("Audited Party") are first made available for inspection
following the Auditing Party's notice of audit. Within that 3-month period, the
Auditing Party shall submit, in writing, all exceptions disclosed by the audit
to the Audited Party. The Audited Party shall have 30 days following receipt of
the exceptions in which to respond in writing to the exceptions. If the Audited
Party fails to respond within that 30-day period, the exceptions shall be deemed
accepted and appropriate adjustments and settlements shall be made and, as
applicable, paid. If the Parties are unable to reach agreement as to any
exceptions to which the Audited Party timely responded within 30 days of the
Audited Party's response, then either Party may submit the matter to arbitration
in accordance with the provisions in Article 9.

ARTICLE 7: FORCE MAJEURE

7.1. In the event a Party is rendered unable, wholly or in part, by Force
Majeure, to carry out its obligations under this Agreement, other than the
obligation to make any payments due hereunder, the obligations of that Party, so
far as they are affected by Force Majeure, shall be suspended from the inception
and during the continuance of the inability, and the cause of the Force Majeure,
as far as possible, shall be remedied with commercially reasonable diligence.
The Party affected by Force Majeure shall provide the other Party with written
notice of the Force Majeure event, with reasonably full detail of the Force
Majeure within a reasonable time after the affected Party learns of the
occurrence of the Force Majeure event. The settlement of strikes, lockouts, and
other labor difficulty shall be entirely within the discretion of the Party
having the difficulty and nothing herein shall require the settlement of
strikes, lockouts, or other labor difficulty.

ARTICLE 8: LIABILITY AND INDEMNIFICATION

8.1. As among the Parties hereto, MarkWest and any of its designees shall be in
custody, control and possession of the Raw Make hereunder, until the Raw Make is
delivered to MEA at the Receipt Point, and shall be in custody control and
possession of the Plant Products after the Plant Products are loaded by MEA into
transportation facilities provided by MarkWest.

8.2. As among the Parties hereto, MEA and any of its designees shall be in
custody, control and possession of the Raw Make hereunder after Raw Make is
delivered at the Receipt Point and shall be in custody, control and possession
of the Plant Products until the Plant Products are loaded by MEA into
transportation facilities provided by MarkWest.

8.3. Each Party ("Indemnifying Party") hereby covenants and agrees with the
other Party, and its affiliates (except for the Indemnifying Party itself), and
each of their directors, officers and employees ("Indemnified Parties"), that
except to the extent caused by the Indemnified Parties' gross negligence or
willful conduct, the Indemnifying Party shall protect, defend,

                        5 of General Terms and Conditions
<Page>

indemnify and hold harmless the Indemnified Parties from, against and in respect
of any and all Losses incurred by the Indemnified Parties to the extent those
Losses arise from or are related to: (a) the Indemnifying Party's facilities; or
(b) the Indemnifying Party's possession and control of the Raw Make or Plant
Products, as applicable.

ARTICLE 9: MISCELLANEOUS

9.1. The failure of any Party hereto to exercise any right granted hereunder
shall not impair nor be deemed a waiver of that Party's privilege of exercising
that right at any subsequent time or times.

9.2. This Agreement shall be governed by, construed, and enforced in accordance
with the laws of the State of Colorado without regard to choice of law
principles.

9.3. This Agreement shall extend to and inure to the benefit of and be binding
upon the Parties, and their respective successors and assigns, including any
assigns of MarkWest's Interests covered by this Agreement. No assignment of this
Agreement shall be binding on either of the Parties until the first day of the
Accounting Period following the date a certified copy of the instrument
evidencing that sale, transfer, assignment or conveyance has been delivered to
the other Party. Further, each assigning Party shall notify its assignee of the
existence of this Agreement and obtain a ratification of this Agreement prior to
such assignment. No assignment by either Party shall relieve that Party of its
continuing obligations and duties hereunder without the express consent of the
other Party.

9.4. Any change, modification or alteration of this Agreement shall be in
writing, signed by the Parties; and, no course of dealing between the Parties
shall be construed to alter the terms of this Agreement.

9.5  This Agreement, including all exhibits and appendices, contains the entire
agreement between the Parties with respect to the subject matter hereof, and
there are no oral or other promises, agreements, warranties, obligations,
assurances, or conditions precedent, affecting it.

9.6  NO BREACH OF THIS AGREEMENT OR CLAIM FOR LOSSES UNDER ANY INDEMNITY
OBLIGATION CONTAINED IN THIS AGREEMENT SHALL CAUSE ANY PARTY TO BE LIABLE FOR,
NOR SHALL LOSSES INCLUDE, ANY DAMAGES OTHER THAN ACTUAL AND DIRECT DAMAGES, AND
EACH PARTY EXPRESSLY WAIVES ANY RIGHT TO CLAIM ANY OTHER DAMAGES, INCLUDING,
WITHOUT LIMITATION, CONSEQUENTIAL, SPECIAL, INDIRECT, PUNITIVE OR EXEMPLARY
DAMAGES.

9.7  DISPUTE RESOLUTION. Any dispute arising under this Agreement ("Arbitrable
Dispute") shall be referred to and resolved by binding arbitration in Denver,
Colorado, by three (3) arbitrators, in accordance with the rules and procedures
of the Judicial Arbiter Group ("JAG"); and, to the maximum extent applicable,
the Federal Arbitration Act (Title 9 of the United States Code). If there is any
inconsistency between this Section and any statute or rules, this Section shall
control. Arbitration shall be initiated within the applicable time limits set
forth in this Agreement and not thereafter or if no time limit is given, within
the time period allowed by the applicable statute of limitations, by one party
("Claimant") giving written notice to the other party ("Respondent") and to JAG,
that the Claimant elects to refer the Arbitrable Dispute to arbitration, and
that the Claimant has appointed an arbitrator, who shall be identified in such
notice. The Respondent shall notify the Claimant and JAG within thirty (30) Days
after receipt of Claimant's notice, identifying the arbitrator the Respondent
has appointed. The two (2) arbitrators so chosen shall select a third arbitrator
within thirty (30) Days after the

                        6 of General Terms and Conditions
<Page>

second arbitrator has been appointed (upon failure of a party to act within the
time specified for naming an arbitrator, such arbitrator shall be appointed by
the administrator's designee). MarkWest shall pay the compensation and expenses
of the arbitrator named by or for it, MEA shall pay the compensation and
expenses of the arbitrator named by or for it, and MarkWest and MEA shall each
pay one-half of the compensation and expenses of the third arbitrator. All
arbitrators must be neutral parties who have never been officers, directors,
employees, contractors or agents of the parties or any of their Affiliates, must
have not less than ten (10) years experience in the oil and gas industry, and
must have a formal financial/accounting, engineering or legal education. The
parties shall have all rights of discovery in accordance with the Federal Rules
of Civil Procedure. The hearing shall be commenced within thirty (30) Days after
the selection of the third arbitrator. The parties and the arbitrators shall
proceed diligently and in good faith in order that the arbitral award shall be
made as promptly as possible. The interpretation, construction and effect of
this Agreement shall be governed by the laws of Colorado, and to the maximum
extent allowed by law, in all arbitration proceedings the laws of Colorado shall
be applied, without regard to any conflicts of laws principles. All statutes of
limitation and of repose that would otherwise be applicable shall apply to any
arbitration proceeding. The tribunal shall not have the authority to grant or
award indirect or consequential damages, punitive damages or exemplary damages.

                        7 of General Terms and Conditions
<Page>

                                    EXHIBIT A

                         PRODUCTS QUALITY SPECIFICATIONS

PROPANE

<Table>
<Caption>
                                                                            TEST METHODS
      PRODUCT CHARACTERISTICS           MINIMUM            MAXIMUM         LATEST REVISION
      -----------------------           -------            -------         ---------------
<S>                                     <C>                <C>             <C>
1.  COMPOSITION                                                                 ASTM E-260
PERCENT BY LIQUID VOLUME:

Ethane                                               As limited by other
                                                     components and vapor
                                                           pressure

HD-5 Propane                              90                 100

Propylene                                                     5

Butanes & Heavier                                            2.5               ASTM D-2163

2.  VAPOR PRESSURE  (psig @ 100                              208               ASTM D-1267
degrees F.)

3.  CORROSION
Copper Strip @ 100 deg. F.                                   1-b               ASTM D-1838

4.  TOTAL SULFUR (PPM by weight                              123               ASTM D-2784
in liquid)

5.  NON-VOLATILE RESIDUE
       a) Milliliters @ 100 deg. F.                          0.05              ASTM D-2158
                       b) Oil Stain                          Pass

</Table>

                        8 of General Terms and Conditions
<Page>

NORMAL BUTANE

<Table>
<Caption>
                                                                            TEST METHODS
      PRODUCT CHARACTERISTICS           MINIMUM            MAXIMUM         LATEST REVISION
      -----------------------           -------            -------         ---------------
<S>                                     <C>                <C>             <C>

1.  COMPOSITION                                                                 ASTM E-260
PERCENT BY LIQUID VOLUME:

Isobutane and Lighter                                         5                ASTM D-2163

Butylene (Percent of N. Butane)                               1

Normal Butane & Butylene                  95                 100                 GPA 2165

Pentanes & Heavier                                            2

2.  VAPOR PRESSURE  (psig @ 100                               50               ASTM D-1267
degrees F.)

3.  CORROSION
Copper Strip @ 100 deg. F.                                   1-b               ASTM D-1838

4.  TOTAL SULFUR (PPM by weight                              140               ASTM D-3246
in liquid)

5.  VOLATILE RESIDUE
95% Evaporated-Temperature,                                plus 36             ASTM D-1837
degrees F.

</Table>

                        9 of General Terms and Conditions
<Page>

ISOBUTANE

<Table>
<Caption>
                                                                            TEST METHODS
      PRODUCT CHARACTERISTICS           MINIMUM            MAXIMUM         LATEST REVISION
      -----------------------           -------            -------         ---------------
<S>                                     <C>                <C>             <C>

1.  COMPOSITION                                                                 ASTM E-260
PERCENT BY LIQUID VOLUME:

Propane, Propylene and Lighter                                3                ASTM D-2163

Isobutane                                 96                 100

Butylene, Normal Butane & Heavier                             4

2.  VAPOR PRESSURE  (psig @ 100                               62               ASTM D-1267
degrees F.)

3.  CORROSION
Copper Strip @ 100 deg. F.                                   1-b               ASTM D-1838

4.  TOTAL SULFUR (PPM by weight                              140               ASTM D-3246
in liquid)

5.  VOLATILE RESIDUE
95% Evaporated-Temperature,                                plus 16             ASTM D-1837
degrees F.

6.  DRYNESS                                             No free water             Visual

</Table>

                       10 of General Terms and Conditions
<Page>

NATURAL GASOLINE

<Table>
<Caption>
                                                                            TEST METHODS
      PRODUCT CHARACTERISTICS           MINIMUM            MAXIMUM         LATEST REVISION
      -----------------------           -------            -------         ---------------
<S>                                     <C>                <C>             <C>

1.  COMPOSITION                                                                 ASTM E-260
PERCENT BY LIQUID VOLUME:

Butanes and Lighter                                           3                  GPA 2165

Pentanes & Heavier                        97                 100

2.  VAPOR PRESSURE  (psig @ 100                               14                ASTM D-323
degrees F.)

3.  CORROSION
Copper Strip @ 104 deg. F.                                   1-b                ASTM D-130

4.  DOCTOR TEST                                            Negative              GPA 1138

5.  DRYNESS                                             No free water             Visual

6.  COLOR                                                  No Color       Field White Cup Method
            Saybolt No.                 plus 25                               Lab-ASTM D-156

7.  DISTILLATION
        End Point, deg. F.                                   375                ASTM D-216

</Table>

                       11 of General Terms and Conditions

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