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MarkWest Energy Partners, L.P.

155 Inverness Drive West, Suite 200

Englewood, CO 80112-5000

September 15, 2005

Via EDGAR & Hand Delivery

United States Securities and Exchange Commission

450 Fifth Street, N.W.

Washington, D.C. 20549-0305

Attn:          Jill
Davis

Jonathan Duersch

Division of Corporation Finance

Re:  MarkWest Energy Partners, L.P.

Form 10-K for Fiscal Year Ended December 31, 2004

Filed June 24, 2005

Form 10-Q for Fiscal Quarters Ended March 31, 2005 and June 30,
2005

Filed June 24, 2005 and August 9, 2005

File No. 0-21956

Dear Ms. Davis and Mr. Duersch,

On behalf of MarkWest Energy Partners, L.P. (“MarkWest,”
the “Partnership,” “we,” or “our”) and in response to the Securities and
Exchange Commission’s (the “Commission”) staff’s (the “Staff”) August 26,
2005 comment letter addressed to the undersigned (the “Comment Letter”), we are
responding below to the Staff’s comments with respect to MarkWest’s Form 10-K
for the period ended December 31, 2004 filed with the Commission on June 24,
2005 and MarkWest’s Form 10-Qs for the periods ending March 31, 2005
and June 30, 2005 (collectively, the “Periodic Reports”).  Our responses below to the Staff’s comments
are numbered to correspond to the numbering of the comments in the Comment
Letter.

As you will read, we conceptually agree with
a number of the suggested changes and believe they can enhance our
disclosure.  After consultation with our
professional advisors, however, we do not believe that the suggested changes,
individually or in the aggregate, necessitate amendments to our Periodic
Reports because such changes do not result in material changes to such
disclosure, and when viewed in their entirety, our Periodic Reports contain
information adequate for investors to make a fully informed investment decision.  Accordingly, we are proposing to address the
specific disclosures in response to the Staff’s comments described below in our
Quarterly Report on Form 10-Q for the period ending September 30,
2005 and in our Annual Report on Form 10-K for the fiscal year ended December 31,
2005.

Overview of the Industry and Our Business, page 19

1.     Comment:  Please expand your disclosure on page 19 to
explain how the ratios disclosed were calculated and to define your use of the
term gross margin.  Compare and contrast
these measures to the information disclosed in your segment footnote on page 96.

Response:  We will revise future filings to include a
description of how the revenue and gross margin percentages are calculated in
the table on page 19.  Specifically
we will include a disclosure that states: “The revenue and gross margin
percentages in the following table were determined by dividing the revenue and
gross margin for each of the revenue producing activities within our business
segments by total consolidated revenue and total consolidated gross margin”.  Gross Margin is defined on page 3 under “Glossary
of Terms” as revenues less purchased product costs.  We have
confirmed the accuracy of our disclosure regarding revenue and gross margin
percentages using the information in the segment footnote on page 96 as
follows:

Revenue
Analysis:

Information obtained from “Segment Disclosure” on page 96:

  East

  Other

  Texas

  Oklahoma

  Southwest

  Appalachia

  Michigan

  Total

  Revenues
  2004

  21,932

  133,636

  69,464

  60,658

  15,624

  301,314

  Divided by
  Total Revenue

  301,314

  301,314

  301,314

  301,314

  301,314

  301,314

  Calculated
  percent of Total Revenue

  7

  %

  44

  %

  23

  %

  20

  %

  6

  %

  100

  %

Information obtained from page 17:

  East Texas

  Gas Gathering,

  Processing,

  Condensate

  Settlement

  Oklahoma

  Gas

  Gathering,

  Processing,

  Condensate

  Settlement

  Other Southwest

  Gas Gathering,

  Processing and

  Transportation

  Appalachia

  Gas

  Processing

  Appalachia NGL

  Transportation,

  Fractionation &

  Storage

  Services

  Total

  Appalachia

  Michigan

  Gas

  Gathering

  and

  Processing

  Michigan

  Crude

  Oil

  Transportation

  Total

  Michigan

  Total

  Percent of total revenue

  7

  %

  44

  %

  23

  %

  17

  %

  3

  %

  20

  %

  4

  %

  2

  %

  6

  %

  100

  %

  Difference between Page 96
  and 17

  0

  0

  0

  0

  0

  0

Gross Margin Analysis:

Information obtained from Segment Disclosure on Page 96:

  East

  Other

  Texas

  Oklahoma

  Southwest

  Appalachia

  Michigan

  Total

  Revenues
  2004

  21,932

  133,636

  69,464

  60,658

  15,624

  301,314

  Minus: Purchased
  Product Cost 2004

  (3,669

  )

  (118,325

  )

  (55,519

  )

  (30,031

  )

  (3,990

  )

  (211,534

  )

  Gross margin
  2004

  18,263

  15,311

  13,945

  30,627

  11,634

  89,780

  Divided by
  total gross margin

  89,780

  89,780

  89,780

  89,780

  89,780

  89,780

  Calculated percent
  of total gross
  margin

  20

  %

  17

  %

  16

  %

  34

  %

  13

  %

  100

  %

Information obtained from page 17:

  East Texas

  Gas Gathering,

  Processing,

  Condensate

  Settlement

  Oklahoma

  Gas

  Gathering,

  Processing,

  Condensate

  Settlement

  Other Southwest

  Gas Gathering,

  Processing and

  Transportation

  Appalachia

  Gas

  Processing

  Appalachia NGL

  Transportation,

  Fractionation &

  Storage

  Services

  Total

  Appalachia

  Michigan

  Gas

  Gathering

  and

  Processing

  Michigan

  Crude

  Oil

  Transportation

  Total

  Michigan

  Total

  Percent of total gross margin

  20

  %

  17

  %

  16

  %

  23

  %

  11

  %

  34

  %

  8

  %

  5

  %

  13

  %

  100

  %

  Difference between Page 96 and 17

  0

  0

  0

  0

  0

  0

Financial Statements

Basis of Presentation, page 72

2.     Comment:  Please expand your basis of presentation accounting policy
to disclose the principles under which you determine whether an entity is
consolidated.  In this regard, please
expand your disclosure to describe how you determine consolidation is
appropriate and whether you have interests in unconsolidated entities and the
related methods used to account for those interests.

Response:  By way of background, at December 31, 2004,
the Partnership owned 100% of all of its subsidiaries, except for a 90%
ownership interest in Bright Star and a 37.5% ownership interest in Texana,
subsidiaries engaged in the gathering and transportation of natural gas.  We consolidate Bright Star and we account for
Texana using the equity method.  Our
investment in Texana was $0.2 million at December 31, 2004 and at June 30,
2005.  We have no subsidiaries that are
recorded under the cost method.

On March 31, 2005, the Partnership acquired
a 50% non-operating membership interest in Starfish Pipeline Company, LLC, (“Starfish”)
from an affiliate of Enterprise Products Partners, L.P. for $41.7 million.  As disclosed in our Quarterly Report on Form 10-Q
for the period ending March 31, 2005, Starfish is a joint venture with
Enbridge Offshore Pipelines LLC, which we account for utilizing the equity
method.  Our investment in Starfish was
$42.0 million at June 30, 2005.

The Partnership will revise future filings to
include a description of the principles under which we determine whether an
entity is consolidated.  Specifically we
will add the following disclosure to the description of our accounting
policies:

“The Partnership’s consolidated financial
statements include the accounts of all majority-owned or controlled
subsidiaries. Equity investments in
which we exercise significant influence but do not control and are not the
primary beneficiary are accounted for using the equity method. Investments in
which we are not able to exercise significant influence over the investee are
accounted for under the cost method.”

Revenue Recognition, page 75

3.     Comment:  We note your description of
various types of contracts with customers beginning on pages 17 through 20
and 31.  Please expand your accounting
policy to address the nature of these contracts and your revenue recognition
accounting policy for each.  Additionally
explain in your disclosure how you have applied the revenue recognition
principles in SAB Topic 13.A to the contractual terms of your arrangements and
your operations.

Response:
The
Partnership generates the majority of its revenues from natural gas gathering,
processing and transmission, NGL transportation, fractionation and storage, and
crude oil gathering and transportation.
While all of these services constitute midstream energy operations, the
Partnership provides its services pursuant to six different types of
arrangements.  In many cases, the
Partnership provides services under contracts that contain a combination of
more than one of the arrangements.  The
following is a description of our six arrangements.

Fee-based arrangements - Under fee-based arrangements,
the Partnership receives a fee or fees for one or more of the following
services: gathering, processing, and transmission of natural gas,
transportation, fractionation and storage of NGLs, and gathering and
transportation of crude oil.  The revenue
the Partnership earns from these contracts is directly related to the volume of
natural gas, NGLs or crude oil that flows through its systems and facilities
and is not directly dependent on commodity prices.

Percent-of-proceeds arrangements - Under percent-of-proceeds
arrangements, the Partnership gathers and processes natural gas on behalf of
producers, sells the resulting residue natural gas and NGLs at market prices
and remits to the producers an agreed upon percentage of the proceeds based on
an index price.  In other cases, instead
of remitting cash payments to the producer, MarkWest

Energy
delivers an agreed upon percentage of the residue gas and NGLs to the producer
and sells the volumes it retains to third parties at market prices.

Percent-of-index arrangements- Under percent-of-index arrangements, the
Partnership generally purchases natural gas at either (1) a percentage
discount to a specified index price, (2) a specified index price less a
fixed amount or (3) a percentage discount to a specified index price less
an additional fixed amount. MarkWest Energy then gathers and delivers the
natural gas to pipelines where it resells the natural gas at the index price.

Keep-whole arrangements - Under keep-whole
arrangements, the Partnership gathers natural gas from the producer, processes
the natural gas and sells the resulting NGLs to third parties at market
prices.  Because the extraction of the
NGLs from the natural gas during processing reduces the Btu content of the
natural gas, the Partnership must either purchase natural gas at market prices
to return to the producers or make a cash payment to the producers equal to the
difference in the energy content of the natural gas processed before and after
processing.

Settlement margin - Under settlement margin, we are
allowed to retain a fixed percentage of the natural gas volume gathered to
cover the compression fuel charges and deemed line losses.  To the extent our gathering systems are
operated more efficiently than the specified contractual allowance, we are
entitled to retain the difference for our own account.

Condensate sales - During the gathering process,
thermodynamic forces contribute to changes in operating conditions of the
natural gas flowing through the pipeline infrastructure.  As a result, hydrocarbon dew points are
reached, causing condensation of hydrocarbons in the high-pressure
pipelines.  Under these arrangements,
condensate collected in the system is retained by us and sold at market prices.

In
general, the accounting guidance provides that revenue should not be recognized
until it is realized and earned.
Concepts Statement 5, paragraph 83(b) states that “an entity’s
revenue-earning activities involve delivering or producing goods, rendering
services, or other activities that constitute its ongoing major or central
operations, and revenues are considered to have been earned when the entity has
substantially accomplished what it must do to be entitled to the benefits
represented by the revenues”.  Paragraph
84(a) states that “the two conditions (being realized or realizable and
being earned) are usually met by the time product or merchandise is delivered
or services are rendered to customers, and revenues from manufacturing and
selling activities and gains and losses from sales of other assets are commonly
recognized at time of sale (usually meaning delivery).”  SAB Topic 13.A addresses general revenue
recognition issues related to revenue being realized and earned.  Under SAB Topic 13.A, revenue generally is
considered realized and earned when persuasive evidence of an arrangement
exists, delivery has occurred or services have been rendered, the fee is fixed
or determinable and collectibility is probable.

Under all six arrangements, revenue is
recognized at the time the product is delivered and title is transferred.  It is upon delivery and transfer of title
that the Partnership meets all four revenue recognition criteria, and it is at
such time that the Partnership recognizes revenue.

The Partnership’s assessment of each of the
four revenue recognition criteria as they relate to its revenue producing
activities is as follows:

Persuasive evidence of an arrangement exists. The Partnership’s customary practice
is to enter into a written contract, executed by both the customer and the
Partnership.

Delivery.  Delivery
is deemed to have occurred at the time the product is delivered and title is
transferred, or in the case of fee-based arrangements, when the services are
rendered.  To the extent we retain our equity liquids as inventory,
delivery occurs when the inventory is subsequently sold and title is
transferred to the third party purchaser.

The fee is fixed or determinable.
The Partnership negotiates the fee for its services at the outset of its
fee-based arrangements. In these arrangements, the fees are nonrefundable. The
fees are generally due within ten days of delivery or services rendered. For
other arrangements, the amount of revenue is determinable when the sale of the
applicable product has been completed upon delivery and transfer of tile. Proceeds
from the sale of products are generally due in ten days.

Collectibility is probable. Collectibility is
evaluated on a customer-by-customer basis. New and existing customers are
subject to a credit review process, which evaluates the customers’ financial
position (e.g. cash position and credit rating) and their ability to pay. If
collectibility is not considered probable at the outset of an arrangement in
accordance with the Partnership’s credit review process, revenue is recognized
when the fee is collected.

In order to enhance our disclosures, we will
add a description of our revenue recognition policies and how we have applied
the revenue recognition principles in SAB Topic 13.A. in our future filings as
follows:

The
Partnership generates the majority of its revenues from natural gas gathering,
processing and transmission, NGL transportation, fractionation and storage, and
crude oil gathering and transportation.
While all of these services constitute midstream energy operations, the
Partnership provides its services pursuant to six different types of
arrangements.  In many cases, the
Partnership provides services under contracts that contain a combination of
more than one of the arrangements.  The
following is a description of our six arrangements.

Fee-based arrangements - Under fee-based arrangements,
the Partnership receives a fee or fees for one or more of the following
services: gathering, processing, and transmission of natural gas,
transportation, fractionation and storage of NGLs, and gathering and
transportation of crude oil.  The revenue
the Partnership earns from these contracts is directly related to the volume