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 Exhibit 4.23  

Execution Version

REGISTRATION RIGHTS AGREEMENT  

between 

MARKWEST ENERGY PARTNERS, L.P.

and

M&R MWE LIBERTY, LLC

dated 

December 29,
2011 

 

 
 

  TABLE OF CONTENTS    
    

 

							
	 
	 	 ARTICLE I DEFINITIONS
	 	 	 	 
	 Section 1.01
	 	 Definitions
	 	 	

1	 
	 
	 	 ARTICLE II REGISTRATION RIGHTS
	 	 	 	 
	 Section 2.01
	 	 Shelf Registration
	 	 	

4	 
	 Section 2.02
	 	 Piggyback Rights
	 	 	5	 
	 Section 2.03
	 	 Underwritten Offering
	 	 	7	 
	 Section 2.04
	 	 Continuous Equity Programs
	 	 	8	 
	 Section 2.05
	 	 Sale Procedures
	 	 	8	 
	 Section 2.06
	 	 Cooperation by Holders
	 	 	11	 
	 Section 2.07
	 	 Restrictions on Sale by Holders of Registrable Securities
	 	 	11	 
	 Section 2.08
	 	 Expenses
	 	 	11	 
	 Section 2.09
	 	 Indemnification
	 	 	11	 
	 Section 2.10
	 	 Limitations on Subsequent Registration Rights
	 	 	13	 
	 Section 2.11
	 	 Transfer or Assignment of Registration Rights
	 	 	13	 
	 
	 	 ARTICLE III MISCELLANEOUS
	 	 	 	 
	 Section 3.01
	 	 Communications
	 	 	

14	 
	 Section 3.02
	 	 Successors and Assigns
	 	 	15	 
	 Section 3.03
	 	 Interpretations
	 	 	15	 
	 Section 3.04
	 	 Confidentiality
	 	 	15	 
	 Section 3.05
	 	 Recapitalization, Exchanges, Etc. Affecting the Registrable Securities
	 	 	16	 
	 Section 3.06
	 	 Specific Performance
	 	 	16	 
	 Section 3.07
	 	 Counterparts
	 	 	16	 
	 Section 3.08
	 	 Applicable Law, Submission to Jurisdiction
	 	 	16	 
	 Section 3.09
	 	 Waiver of Jury Trial
	 	 	17	 
	 Section 3.10
	 	 Severability of Provisions
	 	 	17	 
	 Section 3.11
	 	 Entire Agreement
	 	 	17	 
	 Section 3.12
	 	 Amendment
	 	 	17	 
	 Section 3.13
	 	 No Presumption
	 	 	17	 
	 Section 3.14
	 	 Obligations Limited to Parties to this Agreement
	 	 	17	 

 

 i

 

 

 
 

  REGISTRATION RIGHTS AGREEMENT    
    

        This REGISTRATION RIGHTS AGREEMENT, dated December 29, 2011, (this
"Agreement"), is entered into by and between MARKWEST ENERGY PARTNERS, L.P., a Delaware limited partnership
("MWE") and M&R MWE Liberty, LLC, a Delaware limited liability company (the "Acquirer"). 

        WHEREAS,
this Agreement is made in connection with the closing of the transactions contemplated by that certain Contribution Agreement, of even date herewith by and among MWE, MarkWest
Liberty Gas Gathering, L.L.C., a Delaware limited liability company and the Acquirer (the "Contribution Agreement"); and 

        WHEREAS,
MWE has agreed to provide the registration and other rights set forth in this Agreement for the benefit of the Acquirer pursuant to the Contribution Agreement. 

        NOW
THEREFORE, in consideration of the mutual covenants and agreements set forth herein and for good and valuable consideration, the receipt and sufficiency of which is hereby
acknowledged by each party hereto, the parties hereby agree as follows: 

 
 

  ARTICLE I
  DEFINITIONS    
    

        Section 1.01    Definitions.    As used in this Agreement, the following terms have the meanings indicated: 

        "Acquirer" is defined in the introductory paragraph of this Agreement. 

        "Acquirer Group Member" means the Acquirer or any Person that is directly or indirectly Controlled by the Acquirer and / or to whom
Converted Units or Class B Units are Disposed of in a Disposition made in compliance with the transfer restrictions applicable to the Acquirer set forth in Sections 4.6(e) and 4.6(f) of,
and elsewhere in, the MWE Partnership Agreement. 

        "Affiliate" means with respect to any Person, any Person that, directly or indirectly, Controls, is Controlled by, or is under a common
Control with, such Person. With respect to any natural person, the term "Affiliate" shall also mean (a) the spouse or children (including those by adoption) and siblings of such Person; and any
trust whose primary beneficiary is such Person, such Person's spouse, such Person's siblings and/or one or more of such Person's lineal descendants, (b) the legal representative or guardian of
such Person or of any such immediate family member in the event such Person or any such immediate family member becomes mentally incompetent and (c) any Person controlled by or under the common
control with any one or more of such Person and the Persons described in clauses (a) or (b) of this definition. 

        "Agreement" is defined in the introductory paragraph of this Agreement. 

        "Business Day" means Monday through Friday of each week, except that a legal holiday recognized as such by the government of the United
States of America or the States of Colorado or Texas shall not be regarded as a Business Day. 

        "Class B Unit" means a Class B Unit representing a limited partner interests in MWE, having the terms set forth therefore in
the MWE Partnership Agreement. 

        "Commission" means the United States Securities and Exchange Commission. 

        "Common Unit" means a Common Unit representing a limited partner interest in MWE, having the terms set forth therefore in the MWE
Partnership Agreement. 

        "Confidential Information" is defined in Section 3.04. 

1

 

        "Continuous Equity Program" means any continuous equity program, "at-the-market" program, "dribble out" program or
similar continuous equity transaction program under which MWE engages one or more investment banks or other broker-dealers to act as distribution agents in continuous registered offerings of Common
Units to the public. 

        "Contribution Agreement" is defined in the recitals of this Agreement. 

        "Control," including the correlative terms "Controlling," and
"Controlled by" means the possession, direct or indirect, of the power to direct or cause the direction of the management and policies of a Person,
whether through ownership of voting securities, by contract or otherwise. 

        "Converted Unit" means a Common Unit issuable upon the conversion of a Class B Unit that is issued to the Acquirer pursuant to the
Contribution Agreement at the closing of the transactions contemplated thereby. 

        "Disposition," including the correlative term "Disposed of," means any transaction by
which the holder of a Common Unit or a Class B Unit directly or indirectly assigns such Common Unit or Class B Unit to another Person, and includes a sale, assignment, gift, pledge,
encumbrance, hypothecation, mortgage, exchange or any other disposition by operation of law or otherwise. 

        "Effective Date" means, with respect to a particular Shelf Registration Statement, the date of effectiveness of such Shelf Registration
Statement. 

        "Effectiveness Period" is defined in Section 2.01(a). 

        "Exchange Act" means the Securities Exchange Act of 1934, as amended, supplemented or restated from time to time and any successor to such
statute. 

        "Governmental Authority" means any executive, legislative, judicial, regulatory or administrative agency, body, commission, department,
board, court, tribunal, arbitrating body or authority of the United States or any foreign country, or any state, local or other governmental subdivision thereof. 

        "Holder" means a record holder of Registrable Securities. 

        "Included Registrable Securities" is defined in Section 2.02(a). 

        "Launch Date" is defined in Section 2.02(a). 

        "Law" means any law, statute, code, ordinance, order, rule, rule of common law, regulation, judgment, decree, injunction, franchise,
permit, certificate, license or authorization of any Governmental Authority. 

        "Losses" is defined in Section 2.09(a). 

        "Managing Underwriter" means, with respect to any Underwritten Offering, the book running lead manager of such Underwritten Offering. 

        "Maximum Underwritten Offering Amount" means, with respect to any Underwritten Offering Request that Holders of
Registrable Securities desire to make pursuant to Section 2.03, a number of Registrable Securities equal to 25 times the average daily trading volume for Common Units on the principal National
Securities Exchange on which Common Units are then listed or admitted to trading for Common Units for the 30 consecutive trading days ending on the close of trading on the last trading day preceding
the date of such desired Underwritten Offering Request. 

        "Minimum Underwritten Offering Amount" means, with respect to any Underwritten Offering Request that Holders of
Registrable Securities desire to make pursuant to Section 2.03, a number of Registrable
Securities equal to 10 times the average daily trading volume for Common Units on the principal National Securities Exchange on which Common Units are then listed or admitted to trading 

2

 

for
Common Units for the 30 consecutive trading days ending on the close of trading on the last trading day preceding the date of such desired Underwritten Offering Request. 

        "MWE" is defined in the introductory paragraph. 

        "MWE Partnership Agreement" means the Third Amended and Restated Agreement of Limited Partnership of MarkWest Energy
Partners, L.P., dated effective as of February 21, 2008, as amended by Amendment No. 1 to Third Amended and Restated Agreement of Limited Partnership of MarkWest Energy
Partners, L.P., dated as of even date with this Agreement. 

        "National Securities Exchange" means an exchange registered with the Commission under Section 6(a) of the Exchange Act, or the
NASDAQ Stock Market or any successor thereto. 

        "Opt-Out Notice" is defined in Section 2.02(a). 

        "Other Holders" is defined in Section 2.02(c). 

        "Person" means an individual or a corporation, limited liability company, partnership, joint venture, trust, unincorporated organization,
association, government agency or political subdivision thereof or other entity. 

        "Piggyback Offering" is defined in Section 2.02(a). 

        "Pricing Date" is defined in Section 2.02(a). 

        "Registrable Securities" means each Converted Unit, in all cases only until the earliest to occur of the following: (a) when a
registration statement covering such Converted Unit becomes or has been declared effective by the Commission and such Converted Unit has been Disposed of pursuant to such registration statement;
(b) when such Converted Unit (or the Class B Unit to which such Converted Unit relates) is held by MWE or one of its subsidiaries; (c) when such Converted Unit (or the
Class B Unit to which such Converted Unit relates) is Disposed of to a Person other than an Acquirer Group Member, whether such Disposition is made pursuant to Rule 144 (or any similar
provision then in force) under the Securities Act or otherwise (provided that this definition does not, for the avoidance of doubt, modify the transfer
restrictions applicable to the Acquirer and its Affiliates set forth in Sections 4.6(e) and 4.6(f) of, and elsewhere in, the MWE Partnership Agreement); and (d) when such Converted Unit,
if previously Disposed of to an Acquirer Group Member, becomes directly or indirectly beneficially owned by a Person who, at any time, is not an Acquirer Group Member (as a result of a change of
control of the Acquirer Group Member to whom such Converted Unit was previously Disposed or otherwise). 

        "Registration Expenses" is defined in Section 2.08(a). 

        "Securities Act" means the Securities Act of 1933, as amended, supplemented or restated from time to time and any successor to such
statute. 

        "Selling Expenses" is defined in Section 2.08(a). 

        "Selling Holder" means a Holder who is selling Registrable Securities under a registration statement pursuant to the terms of this
Agreement. 

        "Selling Holder Documentation" is defined in Section 2.02(a). 

        "Shelf Registration Statement" means a registration statement under the Securities Act to permit the public resale of Registrable
Securities from time to time as permitted by Rule 415 of the Securities Act (or any similar provision then in force under the Securities Act). 

        "Underwritten Offering" means an offering (including an offering pursuant to a Shelf Registration Statement) in which Common Units are
sold to an underwriter on a firm commitment basis for 

3

 

reoffering
to the public. For purposes of this Agreement, an offering or sale pursuant to a Continuous Equity Program shall not be considered an Underwritten Offering. 

        "Underwritten Offering Request" is defined in Section 2.03(a). 

 
 

  ARTICLE II
  REGISTRATION RIGHTS    
    

        Section 2.01    Shelf Registration.    

        (a)    Shelf Registration.    MWE shall use its commercially reasonable best efforts to (i) prepare and file
one Shelf Registration Statement under the Securities Act covering the Registrable Securities and (ii) cause such Shelf Registration Statement to become effective no later than July 1,
2013. To the extent that such Shelf Registration Statement does not become effective on or prior to July 1, 2013, other than at the fault of a Selling Holder, without the prior written consent
of the Holders of a majority of the Registrable Securities, MWE will not sell equity securities for its own account in an Underwritten Offering until such Shelf Registration Statement is effective.
The Shelf Registration Statement filed pursuant to this Section 2.01(a) shall be on such appropriate registration form of the Commission as shall
be selected by MWE; provided, however, that if a prospectus supplement will be used in connection with
the marketing of an Underwritten Offering from such Shelf Registration Statement and the Managing Underwriter at any time shall notify MWE in writing that, in the reasonable judgment of such Managing
Underwriter, inclusion of detailed information to be used in such prospectus supplement is of material importance to the success of the Underwritten Offering of such Registrable Securities, MWE shall
use its commercially reasonable efforts to include such information in the prospectus supplement. MWE will use its commercially reasonable efforts to cause the Shelf Registration Statement filed
pursuant to this Section 2.01(a) to be continuously effective under the Securities Act until the earliest date on which any of the following
occurs: (i) all Registrable Securities covered by such Shelf Registration Statement have been distributed in the manner set forth and as contemplated in such Shelf Registration Statement,
(ii) there are no longer any Registrable Securities covered by such Shelf Registration Statement outstanding and (iii) July 1, 2019 (the "Effectiveness
Period"). The Shelf Registration Statement filed pursuant to this Section 2.01(a) when it becomes or is declared
effective (including the documents incorporated therein by reference) will comply as to form in all material respects with all applicable requirements of the Securities Act and the Exchange Act and
will not contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading (and, in the case of
any prospectus contained in such Shelf Registration Statement, in the light of the circumstances under
which a statement is made). As soon as practicable following the Effective Date of the Shelf Registration Statement filed pursuant to this  Section 2.01(a), but in any event within three Business
Days of such date, MWE will notify the Selling Holders of the effectiveness of such Shelf
Registration Statement. 

        (b)    Maximum Shelf Registration Rights; Delay Rights.    

          (i)  Notwithstanding
anything to the contrary contained in this Agreement, MWE shall not be obligated to file or effect more than one Shelf Registration Statement (including
any post-effective amendments to such Shelf Registration Statement filed for the primary purpose of including Selling Holders or adding Converted Units to such Shelf Registration
Statement) pursuant to Section 2.01(a). 

4

 

 

         (ii)  Notwithstanding
anything to the contrary contained in this Agreement, MWE may, upon written notice to any Selling Holder whose Registrable Securities are included in
the Shelf Registration Statement filed pursuant to Section 2.01(a), suspend such Selling Holder's use of any prospectus that is a part of such
Shelf Registration Statement (in which event the Selling Holder shall discontinue sales of the Registrable Securities pursuant to the Shelf Registration Statement) if (A) MWE is pursuing an
acquisition, merger, reorganization, disposition or other similar transaction and MWE determines in good faith that MWE's ability to pursue or consummate such a transaction would be materially and
adversely affected by any required disclosure of such transaction in the Shelf Registration Statement or (B) MWE has experienced some other material non-public event the disclosure
of which at such time, in the good faith judgment of MWE, would materially and adversely affect MWE; provided,  however, that in no event shall the Selling
Holders be suspended from selling Registrable Securities pursuant to the Shelf Registration Statement for a
period that exceeds an aggregate of 60 days in any 180 day period or 90 days (exclusive of days covered by any lock-up agreement executed by a Selling Holder in
connection with any Underwritten Offering by MWE or a Selling Holder) in any 365 day period. Upon disclosure of such information or the termination of the conditions described above, MWE shall
provide prompt notice to the Selling Holders whose Registrable Securities are included in the Shelf Registration Statement, and shall promptly terminate any suspension of sales it has put into effect
and shall take such other actions necessary or appropriate to permit registered sales of Registrable Securities as contemplated in this Agreement. 

        Section 2.02    Piggyback Rights.    

        (a)    Underwritten Offering Piggyback Rights.    If at any time during the Effectiveness Period MWE proposes to
file (i) a prospectus supplement to an effective shelf registration statement, other than the Shelf Registration Statement contemplated by  Section 2.01(a), or (ii) a registration
statement (other than: (A) a shelf registration statement; (B) a registration
relating solely to employee benefit plans; (C) a registration relating solely to a Rule 145 transaction; or (D) a registration on any registration form which does not permit
secondary sales), in either case, for the sale of Common Units in an Underwritten Offering for its own account, then, as soon as practicable but not less than two Business Days prior to the date such
Underwritten Offering is expected to be launched (the "Launch Date") (1) MWE shall notify the Holders of the pendency of the Underwritten
Offering and such notice shall offer the Holders the
opportunity to include in such Underwritten Offering such number of Registrable Securities (the "Included Registrable Securities") as each such Holder
may request in writing (a "Piggyback Offering") and (2) if the Holders propose to include Included Registrable Securities in the Underwritten
Offering, then the Managing Underwriter of the Underwritten Offering shall, no later than the two Business Days prior to the expected Launch Date, provide to the Selling Holders all of the
documentation customarily required for the inclusion of Registrable Securities in the Underwritten Offering, including, without limitation, a custody agreement and
power-of-attorney, Selling Holders' customary representations and warranties, and a form of legal opinion required to be delivered by counsel to the Selling Holders (in form
and substance reasonably acceptable to counsel for the Selling Holders) at the closing of an Underwritten Offering and any over-allotment option closing (collectively, the
"Selling Holder Documentation"). To include Registrable Securities in an Underwritten Offering, each Selling Holder shall, subject to receipt of notice
of the Underwritten Offering and Selling Holder Documentation within the time periods set forth above: (A) complete its review and return the Selling Holder Documentation, with such revisions
as have been agreed to by MWE (such agreement not to be unreasonably withheld) and the Selling Holder, at least one Business Day prior to the expected Launch Date; (B) place the Registrable
Securities eligible for inclusion in an Underwritten Offering into the custody of MWE's transfer agent at least one Business Day prior to the expected Launch Date; (C) agree to participate
following reasonable notice in any due diligence calls arranged by the Managing Underwriter of an Underwritten Offering on the expected Launch Date, the pricing date of an Underwritten Offering (the
"Pricing Date") or in advance of the closing of an Underwritten Offering 

5

 

and
any over-allotment option closing; and (D) unconditionally waive any right to withdraw any Registrable Securities placed into the custody of MWE's transfer agent for inclusion
in an Underwritten Offering within one Business Day of the expected Launch Date, whether on the basis of the offering price, underwriter discount, or for any other reason. Notwithstanding the
foregoing, if MWE has been advised by the Managing Underwriter that the inclusion of Registrable Securities for sale for the benefit of the Holders will have an adverse effect on the price, timing or
distribution of the Common Units, then the amount of Registrable Securities to be offered for the accounts of participating Holders shall be determined based on the provisions of  Section 2.02(c).
If, at any time after giving written notice of its intention to undertake an Underwritten Offering and prior to the closing of
such Underwritten Offering, MWE shall determine for any reason not to undertake or to delay such Underwritten Offering, MWE shall give written notice of such determination to the Selling Holders and,
(i) in the case of a determination not to undertake such Underwritten Offering, shall be relieved of its obligation to sell any Registrable Securities held by the Selling Holders in connection
with such terminated Underwritten Offering, and (ii) in the case of a determination to delay such Underwritten Offering, shall be permitted to delay offering any Registrable Securities held by
the Selling Holders for the same period as the delay of the Underwritten Offering and, so long as (A) such delay is not longer than 10 days and (B) the number of Common Units
intended to be included in the resumed Underwritten Offering by MWE is no more than 20% lower or higher than the number of Common Units that were intended to be included by MWE in such Underwritten
Offering prior to the delay, shall not be required to offer any non-Selling Holders the opportunity to include Registrable Securities in such delayed Underwritten Offering once it is
resumed. Any Selling Holder shall have the right to withdraw such Selling Holder's request for inclusion of such Selling Holder's Registrable Securities in such Underwritten Offering by giving written
notice to MWE of such withdrawal at least one Business Day prior to the Launch Date. Notwithstanding the foregoing, any
Holder may deliver written notice (an "Opt-Out Notice") to MWE requesting that such Holder not receive notice from MWE of any proposed
Underwritten Offering; provided, however, that such Holder may later revoke any such Opt-Out
Notice in writing. For the avoidance of doubt, if a Holder elects to include Registrable Securities in a Piggyback Offering, such included Registrable Securities shall be allocated to the primary
offering of Common Units and to any over-allotment option requested by the Managing Underwriter in the same relative proportions as are the Common Units intended to be included in such
Piggyback Offering by MWE. In the event that following the Launch Date, MWE determines to increase the number of units offered in any Underwritten Offering, MWE shall provide written notice to the
Selling Holders and such Selling Holders shall have the right to increase the number of Registrable Securities offered by such Selling Holders to the extent covered by the Selling Holder Documentation
and subject to the limitations set forth in Section 2.02(b). In the event of any such upsize, the Selling Holders will promptly (and in a manner that
does not unreasonably or materially delay or impair MWE's primary marketing efforts in relation to the anticipated timing of pricing the Underwritten Offering) notify MWE in writing of their intention
to participate in the upsized Underwritten Offering. 

        (b)    Limitation on Piggyback Rights.    Notwithstanding anything to the contrary contained in this Agreement, if, in
connection with an Underwritten Offering contemplated by Section 2.02(a), the total amount of Registrable Securities that Holders propose to
include in such Underwritten Offering would exceed 20% of the total number of Common Units intended to be included in such Underwritten Offering by MWE, then, subject to the limitations set forth in  Section 2.02(c)
, such Holders shall only be entitled to register in such Underwritten Offering a number of Registrable Securities equal to 20% of
the total number of Common Units intended to be included in such Underwritten Offering by MWE (including an equal percentage in any over-allotment option requested by the Managing
Underwriter), with such number to be allocated (i) pro-rata among such Holders based on the percentage determined by dividing (A) the number of Registrable Securities
proposed to be sold by each such Holder in such Underwritten Offering by (B) the aggregate number of Registrable Securities proposed to be sold by all 

6

 

Holders
in such Underwritten Offering or (ii) in such other proportions as such Holders may specify in a written notice delivered to MWE at least one Business Day prior to the Launch Date. 

        (c)    Priority of Piggyback Rights.    Notwithstanding anything to the contrary contained in this Agreement, in
connection with an Underwritten Offering contemplated by Section 2.02(a), if the Managing Underwriter or Managing Underwriters of such
Underwritten Offering advises MWE that the total amount of Common Units that the Selling Holders and any other Persons intend to include in such Underwritten Offering exceeds the number that can be
sold in such Underwritten Offering without being likely to have an adverse effect on the price, timing or distribution of the Common Units offered or the market for the Common Units, then the Common
Units to be included in such Underwritten Offering shall include the number of Common Units that such Managing Underwriter or Managing Underwriters advises MWE can be sold without having such adverse
effect, with such number to be allocated (i) first, pro-rata among MWE and the Selling Holders, based, for MWE and
each such Selling Holder, on the percentage derived by dividing (A) the number of Common Units proposed to be sold by MWE or such Selling Holder in such Underwritten Offering (subject to the
limitations set forth in Section 2.02(b)); by (B) the aggregate number of Common Units proposed to be sold by MWE and all Selling Holders
in the Underwritten Offering (subject to the limitations set forth in Section 2.02(b)) and (ii) second, pro rata among any other Persons
who have been or are granted registration rights on or after the date of this Agreement who have requested participation in the Underwritten Offering (the "Other
Holders") based, for each such Other Holder, (i) on the percentage derived by dividing (A) the number of Common Units proposed to be sold by such Other Holders in
such Underwritten Offering; by (B) the aggregate number of Common Units proposed to be sold by all Other Holders in the Underwritten Offering or (ii) on such other manner as such Other
Holders may agree. 

        Section 2.03    Underwritten Offering.    

        (a)    Request for Underwritten Offering.    From and after January 1, 2017, in the event that Holders of at
least a majority of the Registrable Securities elect to Dispose of Registrable Securities under a Shelf Registration Statement pursuant to an Underwritten Offering, MWE shall, at the request of such
Selling Holders (such request, the "Underwritten Offering Request"), enter into an underwriting agreement in customary form with the Managing
Underwriter or Managing Underwriters, which shall include, among other provisions, indemnities to the effect and to the extent provided in  Section 2.09, and shall take all such other reasonable
actions as are requested by the Managing Underwriter to expedite or facilitate the
Disposition of the Registrable Securities; provided, however, that (i) MWE shall not be required
to effect more than three Underwritten Offerings pursuant to this Section 2.03; (ii) the Holders shall be limited to one Underwritten
Offering Request in any consecutive 365-day period; (iii) MWE shall not be required to effect either of the first two Underwritten Offerings requested pursuant to this  Section 2.03 if the
Holders do not request to register at least the Minimum Underwritten Offering Amount in such Underwritten Offering and
(iv) the Holders shall not be permitted to request to register more than the Maximum Underwitten Offering Amount in any single Underwritten Offering Request. 

        (b)    General Procedures.    In connection with any Underwritten Offering, MWE shall be entitled to select the
Managing Underwriter or Managing Underwriters. In connection with an Underwritten Offering contemplated by this Agreement in which a Selling Holder participates, each Selling Holder and MWE shall be
obligated to enter into an underwriting agreement with the Managing Underwriter or Managing Underwriters that contains such representations, covenants, indemnities and other rights and obligations as
are customary in underwriting agreements for firm commitment offerings of equity securities. No Selling Holder may participate in an Underwritten Offering unless such Selling Holder agrees to sell its
Registrable Securities on the basis provided in such underwriting agreement and completes and executes all questionnaires, powers-of-attorney, indemnities and other documents
reasonably required under the terms of such underwriting agreement. Each Selling Holder may, at its 

7

 

option,
require that any or all of the representations and warranties by, and the other agreements on the part of, MWE to and for the benefit of such underwriters also be made to and for such Selling
Holder's benefit and that any or all of the conditions precedent to the obligations of such underwriters under such underwriting agreement also be conditions precedent to its obligations. No Selling
Holder shall be required to make any representations or warranties to or agreements with MWE or the underwriters other than representations, warranties or agreements regarding such Selling Holder and
its ownership of the securities being registered on its behalf and its intended method of distribution and any other representation required by Law. If any Selling Holder disapproves of the terms of
an Underwritten Offering, such Selling Holder may elect to withdraw therefrom by notice to MWE and the Managing Underwriter; provided,  however, that such
withdrawal must be made at least one Business Day prior to the pricing of such Underwritten Offering to be effective. No such
withdrawal or abandonment shall affect MWE's obligation to pay Registration Expenses. In the event that all Selling Holders holding Registrable Securities subject to such Underwritten Offering,
specifically not including any securities to be sold by MWE or other Persons in such Underwritten Offering, withdraw from such Underwritten Offering, such Underwritten Offering shall not be counted
for purposes of the Underwritten Offering limitations set forth in Section 2.03(a)(i) or (ii). 

        Section 2.04    Continuous Equity Programs.    If at any time during the Effectiveness Period MWE has in place
or has imminent plans to implement a Continuous Equity Program, MWE shall provide prompt notice of the existence or planned implementation of such Continuous Equity Program to the Acquirer and, if
notified by the Acquirer in writing, shall cooperate with the Acquirer to provide the Acquirer the opportunity to, at the election of MWE, either: (a) enter into commercially reasonable
arrangements to include, on behalf of the Acquirer in such Continuous Equity Program Registrable Securities equal to 20% of the total number of Common Units included or intended to be included in such
Continuous Equity Program by MWE; or (b) enter into commercially reasonable alternative arrangements that would permit the Acquirer to resell Registrable Securities equal to 20% of the total
number of Common Units included or intended to be included in such Continuous Equity Program by MWE to the public from time to time, pursuant to Rule 144 or such other method of distribution as
may be agreed between MWE and the Acquirer. If the Acquirer participates in a Continuous Equity Program in accordance with this Section 2.04, the
Acquirer and MWE shall enter into an equity distribution agreement with the distribution agent or distribution agents that contain such representations, covenants, indemnities and other rights and
obligations as are customary in equity distribution agreements for continuous equity transaction programs. The Acquirer will not be permitted to participate in a Continuous Equity Program unless the
Acquirer agrees to sell the applicable Registrable Securities on the basis provided in such equity distribution agreement and completes and executes all questionnaires,
powers-of-attorney, indemnities and other documents reasonably required under the terms of such equity distribution agreement. The Acquirer shall not be required to make any
representations or warranties to or agreements with MWE or the distribution agents other than representations, warranties or agreements regarding the Acquirer and its ownership of the securities to be
subject to such equity distribution agreement and its intended method of distribution and any other representations required by Law. Each Holder shall keep any information relating to any such
Continuous Equity Program confidential and shall not disseminate or in any way disclose such information 

        Section 2.05    Sale Procedures.    In connection with its obligations under this  Article II, MWE will, as expeditiously as possible:

        (a)   prepare
and file with the Commission such amendments and supplements to the Shelf Registration Statement filed pursuant to  Section 2.01(a) and the prospectus used in connection therewith as may be
necessary to keep such Shelf Registration Statement effective for the
Effectiveness Period and as may be necessary to comply with the provisions of the Securities Act with respect to the Disposition of all securities covered by such Shelf Registration Statement; 

8

 

        (b)   furnish
to each Selling Holder (i) as far in advance as reasonably practicable before filing the Shelf Registration Statement to be filed pursuant to  Section 2.01(a) or any other registration
statement contemplated by this Agreement or any supplement or amendment thereto, upon request, copies
of reasonably complete drafts of all such documents proposed to be filed (including exhibits and each document incorporated by reference therein to the extent then required by the rules and
regulations of the Commission, which shall be deemed provided if such exhibits and documents are available on the Commission's website), and provide each such Selling Holder the opportunity to object
to any information pertaining to such Selling Holder and its plan of distribution that is contained therein and make the corrections reasonably requested by such Selling Holder with respect to such
information prior to filing such Shelf Registration Statement or such other registration statement and the prospectus included therein or any supplement or amendment thereto, and (ii) an
electronic copy of such Shelf Registration Statement or such other registration statement and the prospectus included therein and any supplements and amendments thereto as such Selling Holder may
reasonably request in order to facilitate the public sale or other Disposition of the Registrable Securities covered by such Shelf Registration Statement or other registration statement; 

        (c)   if
applicable, use its commercially reasonable efforts to register or qualify the Registrable Securities covered by the Shelf Registration Statement filed pursuant to  Section 2.01(a) or any other
registration statement contemplated by this Agreement under the securities or "blue sky" laws of such jurisdictions
as the Selling Holders or, in the case of an Underwritten Offering, the Managing Underwriter, shall reasonably request; provided,  however, that MWE shall
not be required to qualify generally to transact business in any jurisdiction where it is not then required to so qualify or to
take any action which would subject it to general service of process in any such jurisdiction where it is not then so subject; 

        (d)   promptly
notify each Selling Holder and each underwriter of Registrable Securities, at any time when a prospectus relating thereto is required to be delivered under the
Securities Act, of (i) the filing of the Shelf Registration Statement filed pursuant to Section 2.01(a) or any other registration
statement contemplated by this Agreement or any prospectus or prospectus supplement to be used in connection therewith, or any amendment or supplement thereto, and, with respect to such Shelf
Registration Statement or any other registration statement or any post-effective amendment thereto, when the same has become effective; and (ii) the receipt of any written comments
from the Commission with respect to any filing referred to in clause (i) and any written request by the Commission for amendments or supplements to such Shelf Registration Statement or any
other registration statement or any prospectus or prospectus supplement thereto; 

        (e)   immediately
notify each Selling Holder and each underwriter of Registrable Securities, at any time when a prospectus relating thereto is required to be delivered under
the Securities Act, of (i) the happening of any event as a result of which the prospectus or prospectus supplement contained in the Shelf Registration Statement filed pursuant to  Section 2.01(a) or any other registration statement contemplated by this Agreement, as then in effect, or any supplemental amendment thereto,
includes an untrue statement of a material fact or omits to state any material fact required to be stated therein or necessary to make the statements therein not misleading in light of the
circumstances then existing; (ii) the issuance or threat of issuance by the Commission of any stop order suspending the effectiveness of such Shelf Registration Statement or any other
registration statement contemplated by this Agreement, or the initiation of any proceedings for that purpose; or (iii) the receipt by MWE of any notification with respect to the suspension of
the qualification of any Registrable Securities for sale under the applicable securities or blue sky laws of any jurisdiction. Following the provision of such notice, MWE agrees to as promptly as
practicable amend or supplement the prospectus or prospectus supplement or take other appropriate action so that the prospectus or prospectus supplement does not include an untrue statement of a
material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading in the light of the circumstances 

9

 

then
existing and to take such other action as is necessary to remove a stop order, suspension, threat thereof or proceedings related thereto; 

        (f)    upon
request and subject to appropriate confidentiality obligations, furnish to each Selling Holder copies of all material correspondence with the Commission or any
other governmental agency or self-regulatory body or other body having jurisdiction (including any domestic or foreign securities exchange) relating to such offering of Registrable
Securities; 

        (g)   in
the case of an Underwritten Offering, furnish upon request, (i) an opinion letter of counsel for MWE dated the date of the closing under the underwriting
agreement, including a standard "10b-5" letter and (ii) a "cold comfort" letter dated the Pricing Date of such Underwritten Offering and a letter of like kind dated the date of the
closing under the underwriting agreement, in each case, signed by the independent public accountants who have certified MWE's financial statements included or incorporated by reference into the
applicable registration statement, and each of the opinion and the "cold comfort" letter shall be in customary form and covering substantially the same matters with respect to such registration
statement (and the prospectus included therein and any supplement thereto) and as are customarily covered in opinion letters of issuer's counsel and in accountants' letters delivered to the
underwriters in underwritten offerings of equity securities; 

        (h)   otherwise
use its commercially reasonable efforts to comply with all applicable rules and regulations of the Commission, and make available to its security holders, as
soon as reasonably practicable, an earnings statement, which earnings statement shall satisfy the provisions of Section 11(a) of the Securities Act and Rule 158 promulgated thereunder; 

        (i)    make
available to the appropriate representatives of the Managing Underwriter and Selling Holders access to such information and MWE personnel as is reasonable and
customary to enable such parties to establish a due diligence defense under the Securities Act; provided,  however, that MWE need not disclose any
non-public information to any such representative unless and until such representative has entered
into a confidentiality agreement with MWE reasonably satisfactory to MWE; 

        (j)    cause
all Registrable Securities registered pursuant to this Agreement to be listed on each National Securities Exchange, if any, on which similar securities issued by
MWE are then listed; 

        (k)   use
its commercially reasonable efforts to cause the Registrable Securities to be registered with or approved by such other Governmental Authorities as may be necessary
by virtue of the business and operations of MWE to enable the Selling Holders to consummate the Disposition of such Registrable Securities, subject to the last clause of  Section 2.05(c);

        (l)    provide
a transfer agent and registrar for Registrable Securities covered by the registration statement in respect of any registration of any Registrable Securities not
later than the effective date of such registration statement; and 

        (m)  take
such other actions as are reasonably requested by the Selling Holders or the underwriters, if any, to expedite or facilitate the Disposition of such Registrable
Securities. and 

        Each
Selling Holder, upon receipt of notice from MWE of the happening of any event of the kind described in subsection (e) of this  Section 2.05, shall forthwith discontinue Disposition of the
Registrable
Securities until such Selling Holder's receipt of the copies of the supplemented or amended prospectus contemplated by subsection (e) of this  Section 2.05 or until it is advised in writing by
MWE that the use of the prospectus may be resumed, and has received copies of any additional or
supplemental filings incorporated by reference in the prospectus, and, if so directed by MWE, such Selling Holder will deliver, or will request the Managing Underwriter or Managing Underwriters, if
any, to deliver to MWE all copies in their possession or control, other than permanent file copies then in such Selling Holder's possession, of the prospectus and any prospectus supplement covering
such Registrable Securities current at the time of receipt of such notice. 

10

 

 

        Section 2.06    Cooperation by Holders.    MWE shall have no obligation to include Registrable Securities of a
Holder in a Shelf Registration Statement or in an Underwritten Offering or otherwise under Article II if such Selling Holder has failed to timely
furnish such information that, in the reasonable opinion of counsel to MWE, is reasonably required for such registration statement or prospectus supplement, as applicable, to comply with the
Securities Act. 

        Section 2.07    Restrictions on Sale by Holders of Registrable Securities.    During the Effectiveness Period,
each Holder of Registrable Securities who is included in the Shelf Registration Statement filed pursuant to Section 2.01(a) agrees not to effect
any Disposition of Common Units during the 90 calendar day period beginning on the date that a prospectus supplement or other prospectus (including any free writing prospectus) is filed with the
Commission with respect to an Underwritten Offering of equity securities of MWE; provided that the duration of the foregoing restrictions shall be no
longer than the duration of the shortest restriction generally imposed by the underwriters on the officers, directors or any other unitholder of MWE on whom a restriction is imposed in connection with
such public offering. 

        Section 2.08    Expenses.    

        (a)    Certain Definitions.    "Registration Expenses" means all
expenses incident to MWE's performance under or compliance with this Agreement to effect the registration of Registrable Securities in the Shelf Registration Statement pursuant to  Section 2.01(a),
a Piggyback Offering pursuant to Section 2.02, an Underwritten Offering
pursuant to Section 2.03, or any Continuous Equity Program or other arrangement contemplated by  Section 2.04, and the Disposition of such
securities pursuant thereto, including, without limitation, all customary registration, filing,
securities exchange listing and securities exchange fees, all customary registration, filing, qualification and other fees and expenses of complying with securities or "blue sky" laws, fees of the
Financial Industry Regulatory Authority, Inc., fees of transfer agents and registrars, all word processing, duplicating and printing expenses, the fees and disbursements of counsel to MWE and
independent public accountants for MWE, including the expenses of any special audits or "cold comfort" letters required by or incident to such performance and compliance, and reasonable fees and
expenses of one counsel for the Holders in such registration
as a group (which counsel shall be selected by the Holders of a majority of the Registrable Securities included in such registration). "Selling
Expenses" means all underwriting fees, discounts and selling commissions (and similar fees or arrangements associated with) and transfer taxes allocable to the sale of the
Registrable Securities. 

        (b)    Expenses.    MWE will pay all reasonable Registration Expenses as determined in good faith, including, in the
case of an Underwritten Offering or a Piggyback Offering, whether or not any sale is made pursuant to the related registration statement. Except as otherwise provided in  Section 2.08(a) or
Section 2.09, MWE shall not be responsible for legal fees incurred by
Holders in connection with the exercise of such Holders' rights and obligations under this Agreement, or for any Selling Expenses. Each Selling Holder shall pay all Selling Expenses in connection with
any sale of its Registrable Securities. 

        Section 2.09    Indemnification.    

        (a)    By MWE.    In the event of a registration of any Registrable Securities under the Securities Act pursuant to
this Agreement, MWE will indemnify and hold harmless each Selling Holder, its directors, officers, employees, agents and managers, and each underwriter, pursuant to the applicable underwriting
agreement with such underwriter, of Registrable Securities thereunder and each Person, if any, who controls such Selling Holder or underwriter within the meaning of the Securities Act and the Exchange
Act, and its directors, officers, employees, agents and managers, against any losses, claims, damages, expenses or liabilities (including reasonable attorneys' fees and expenses) (collectively,
"Losses"), joint or several, to which such Selling Holder or underwriter or controlling Person may become subject under the Securities Act, the Exchange
Act or otherwise, insofar as such Losses (or 

11

 

actions
or proceedings, whether commenced or threatened, in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact (in the case of any
prospectus, in the light of the circumstances under which such statement is made) contained in the Shelf Registration Statement filed pursuant to  Section 2.01(a) or any other registration statement
contemplated by this Agreement, any preliminary prospectus or final prospectus contained
therein, or any free writing prospectus related thereto, or any amendment or supplement thereof, or arise out of or are based upon the omission or alleged omission to state therein a material fact
required to be stated therein or necessary to make the statements therein (in the case of a prospectus, in the light of the circumstances under which they were made) not misleading, and will reimburse
each such Selling Holder, its directors and officers, each such underwriter and each such controlling Person for any legal or other expenses reasonably incurred by them in connection with
investigating or defending any such Loss or actions or proceedings; provided, however, that MWE will not
be liable in any such case if and to the extent that any such Loss arises out of or is based upon an untrue statement or alleged untrue statement or omission or alleged omission so made in conformity
with information furnished by such Selling Holder, such underwriter or such controlling Person in writing specifically for use in the Shelf
Registration Statement or such other registration statement, free writing prospectus or prospectus supplement, as applicable. Such indemnity shall remain in full force and effect regardless of any
investigation made by such Selling Holder or any such director, officer, employee, agent, manager or controlling Person, and shall survive the transfer of such securities by such Selling Holder. 

        (b)    By Each Selling Holder.    Each Selling Holder agrees to indemnify and hold harmless MWE, its directors,
officers, employees and agents and each Person, if any, who controls MWE within the meaning of the Securities Act or of the Exchange Act to the same extent as the foregoing indemnity from MWE to the
Selling Holders, but only with respect to information regarding such Selling Holder furnished in writing by or on behalf of such Selling Holder expressly for inclusion in the Shelf Registration
Statement filed pursuant to Section 2.01(a) or any other registration statement contemplated by this Agreement, any preliminary prospectus or
final prospectus contained therein, or any free writing prospectus related thereto, or any amendment or supplement thereof; provided,  however, that the
liability of each Selling Holder shall not be greater in amount than the dollar amount of the proceeds (net of Selling Expenses)
received by such Selling Holder from the sale of the Registrable Securities giving rise to such indemnification. Such indemnity shall remain in full force and effect regardless of any investigation
made by or on behalf of MWE or any such director, officer, employee, agent, manager or controlling Person, and shall survive the transfer of such securities by such Selling Holder. 

        (c)    Notice.    Promptly after any indemnified party has received notice of any indemnifiable claim hereunder, or
the commencement of any action, suit or proceeding by a third person, which the indemnified party believes in good faith is an indemnifiable claim under this Agreement, the indemnified party shall
give the indemnifying party written notice of such claim but failure to so notify the indemnifying party will not relieve the indemnifying party from any liability it may have to such indemnified
party hereunder except to the extent that the indemnifying party is materially prejudiced by such failure. Such notice shall state the nature and the basis of such claim to the extent then known. The
indemnifying party shall be entitled to participate in and, to the extent it shall wish, to assume and undertake the defense thereof with counsel reasonably satisfactory to such indemnified party and,
after notice from the indemnifying party to such indemnified party of its election so to assume and undertake the defense thereof, the indemnifying party shall not be liable to such indemnified party
under this Section 2.09 for any legal expenses subsequently incurred by such indemnified party in connection with the defense thereof other than
reasonable costs of investigation and of liaison with counsel so selected; provided, however, that,
(i) if the indemnifying party has failed to assume the defense and employ counsel or (ii) if the defendants in any such action include both the indemnified party and the indemnifying
party and counsel to the indemnified party shall have concluded that there may be reasonable defenses available to the indemnified party that are different from or additional to 

12

 

those
available to the indemnifying party, or if the interests of the indemnified party reasonably may be deemed to conflict with the interests of the indemnifying party, then the indemnified party
shall have the right to select a separate counsel and to assume such legal defense and otherwise to participate in the defense of such action, with the reasonable out-of-pocket
expenses
and fees of such separate counsel and other reasonable out-of-pocket expenses related to such participation to be reimbursed by the indemnifying party as incurred.
Notwithstanding any other provision of this Agreement, the indemnifying party shall not settle any indemnified claim without the consent of the indemnified party, unless the settlement thereof imposes
no liability or obligation on, and includes a complete release from liability of, and does not contain any admission of wrongdoing by, the indemnified party. 

        (d)    Contribution.    If the indemnification provided for in this  Section 2.09 is held by a court or government agency of
competent jurisdiction to be unavailable to any indemnified party or is insufficient to
hold them harmless in respect of any Losses, then each such indemnifying party, in lieu of indemnifying such indemnified party, shall contribute to the amount paid or payable by such indemnified party
as a result of such Loss in such proportion as is appropriate to reflect the relative fault of the indemnifying party on the one hand and of such indemnified party on the other in connection with the
statements or omissions which resulted in such Losses, as well as any other relevant equitable considerations; provided,  however, that in no event shall a
Selling Holder be required to contribute an aggregate amount in excess of the dollar amount of proceeds (net of
Selling Expenses) received by such Selling Holder from the sale of Registrable Securities giving rise to such indemnification. The relative fault of the indemnifying party on the one hand and the
indemnified party on the other shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a
material fact has been made by, or relates to, information supplied by such party, and the parties' relative intent, knowledge, access to information and opportunity to correct or prevent such
statement or omission. The parties hereto agree that it would not be just and equitable if contributions pursuant to this paragraph were to be determined by pro rata allocation or by any other method
of allocation which does not take account of the equitable considerations referred to herein. The amount paid by an indemnified party as a result of the Losses referred to in the first sentence of
this paragraph shall be deemed to include any legal and other expenses reasonably incurred by such indemnified party in connection with investigating or defending any Loss that is the subject of this
paragraph. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any Person who is not guilty of
such fraudulent misrepresentation. 

        (e)    Other Indemnification.    The provisions of this  Section 2.09 shall be in addition to any other rights to
indemnification or contribution that an indemnified party may have pursuant to Law,
equity, contract or otherwise. 

        Section 2.10    Limitations on Subsequent Registration Rights.    From and after the date of this Agreement,
MWE shall not, without the prior written consent of the Holders of a majority of the Registrable Securities then outstanding, enter into any agreement with any holder or prospective holder of any
securities of the Company that contains priority rights that contravene the priority rights of the Holders under Section 2.02(c);  provided that this
limitation shall not apply to any additional Person who becomes a party to this Agreement in accordance with  Section 2.11. This Section 2.10 does
not limit or restrict any outstanding agreements
providing for registration rights between MWE and any other Person(s) entered into prior to the date of this Agreement. 

        Section 2.11    Transfer or Assignment of Registration Rights.    The rights to cause MWE to register
Registrable Securities granted to the Acquirer by MWE under this Article II may be transferred or assigned by a
Holder to a transferee or assignee; provided, that the transferee or assignee is an Acquirer Group Member. The transferor shall give written notice to
MWE at least ten Business Days prior to any said transfer or assignment, setting forth the information required under Section 3.01 for each such
transferee and identifying the securities with respect to which such registration rights are 

13

 

being
transferred or assigned, and each such transferee shall agree in writing to be subject to all of the terms and conditions of this Agreement. 

 
 

  ARTICLE III
  MISCELLANEOUS    
    

        Section 3.01    Communications; Holder Representative.    

        (a)   All
notices and demands provided for hereunder shall be in writing and shall be given by hand delivery, electronic mail, facsimile, registered or certified mail, return
receipt requested, regular mail, or air courier guaranteeing overnight delivery to the following addresses: 

(i)    If
to the Acquirer: 

c/o
M&R MWE Liberty, LLC

811 Main Street, Suite 4200

Houston, Texas 77002

Attention: Holder Representative 

Facsimile:
(713) 579-5010 

Electronic
mail: jraymond@emgtx.com

                           jrawls@emgtx.com

                           pwade@emgtx.com 

with
a copy (which shall not constitute notice) to: 

Locke
Lord LLP

600 Travis Street, Suite 2800

Houston, Texas 77002

Attention: H. William Swanstrom 

Electronic
mail: bswanstrom@lockelord.com 

(ii)    If
to MWE: 

MarkWest
Energy Partners, L.P.

1515 Arapahoe Street

Tower 1, Suite 1600

Denver, Colorado 80202-2126

Attention:    Senior Vice President and Chief Financial Officer

                    Senior Vice President and General Counsel 

Facsimile:
(303) 925-9305 

Electronic
mail:    nbuese@markwest.com

                              cbromley@markwest.com 

or,
if to a transferee of the Acquirer, to the transferee at the addresses provided pursuant to Section 2.10. All notices and communications
shall be deemed to have been duly given: (i) at the time delivered by hand, if personally delivered; (ii) when notice is sent to the recipient provided that confirmation of receipt is
obtained by sender orally, by facsimile or by electronic mail if sent by electronic mail; (iii) upon confirmation of delivery, if sent by facsimile; (iv) upon actual receipt if sent by
registered or certified mail, return receipt requested, or regular mail, if mailed; and (v) upon actual receipt when delivered to an air courier guaranteeing overnight delivery. 

        (b)   John
T. Raymond is hereby appointed by the Acquirer and by any Person who may become a Holder from time to time (and their respective successors and assigns) as agent
and attorney-in-fact 

14

 

with
full power of substitution (the "Holder Representative") for the Acquirer and each such other Holder as the party authorized to: (i) to
elect to exercise, or not exercise, any and all rights of the Acquirer and any such Holder arising under this Agreement, including those relating to the exercise of rights in respect of Underwritten
Offerings under Article II; (ii) consent to and execute any amendment, waiver or consent of or under this Agreement; and (iii) give and receive notices, demands and other
communications to or from the Acquirer or any such other Holder relating to the this Agreement and the transactions contemplated by this Agreement, in each case without having to seek or obtain the
consent of the Acquirer or any such other Holder. The Holders may at any time remove and replace the Holder Representative by providing written notice thereof, executed by the Holders of at least a
majority of the Registrable Securities to MWE. 

        (c)   Notwithstanding
anything to the contrary in this Agreement, wherever any notice, demand or other communication to the Acquirer, any other Holder or any group of Holders,
or any Selling Holder or group of Selling Holders (including any such notice, demand or other communication under Article II) is provided for in this Agreement, such notice, demand or other
communication shall be deemed duly given if delivered to the Holder Representative. MWE shall be entitled to act in full reliance and shall be protected from acting in reliance upon any notice, demand
or other communication from the Holder Representative on behalf of the Acquirer, any other Holder or any group of Holders, or any Selling Holder or group of Selling Holders. 

        Section 3.02    Successors and Assigns.    This Agreement shall inure to the benefit of and be binding upon the
successors and assigns of each of the parties, including subsequent Holders of Registrable Securities to the extent permitted herein. 

        Section 3.03    Interpretations.    In this Agreement, unless a clear contrary intention appears:
(a) the singular includes the plural and vice versa; (b) reference to a Person includes such Person's successors and assigns but, in the case of a party, to this Agreement only if such
successors and assigns are permitted by this Agreement, and reference to a Person in a particular capacity excludes such Person in any other capacity; (c) reference to any gender includes each
other gender; (d) references to any Section, Article, subsection and other subdivision refer to the corresponding Sections, Articles, subsections and other subdivisions of this Agreement unless
expressly provided otherwise; (e) references in any Section or Article or definition to any clause means such clause of such Section, Article or definition; (f) "hereunder," "hereof,"
"hereto" and words of similar import are references to this Agreement as a whole and not to any particular provision of this Agreement; (g) the word "or" is not exclusive, and the word
"including" (in its various forms) means "including without limitation"; (h) references to "days" are to calendar days; and (i) all references to money refer to the lawful currency of
the United States.
The table of contents and Article and Section titles and headings in this Agreement are inserted for convenience of reference only and are not intended to be a part of, or to affect the meaning or
interpretation of, this Agreement. Whenever any determination, consent or approval is to be made or given by MWE under this Agreement, such action shall be in the MWE's sole discretion unless
otherwise specified. 

        Section 3.04    Confidentiality.    The Acquirer agrees that all information that is not generally available to
the public that is disclosed to the Acquirer pursuant to this Agreement, including any information regarding the expected price, timing or distribution of the Common Units expected be offered or the
market for the Common Units in any Underwritten Offering ("Confidential Information"), shall be kept confidential by the Acquirer unless such
Confidential Information (a) is known or becomes known to the public in general (other than as a result of a breach of this Section 3.04
by the Acquirer or any Person to whom Acquirer discloses such Confidential Information) or (b) is or has been made known or disclosed to the Acquirer by a third party without a breach of any
obligation of confidentiality such third party may have to MWE; provided, however, that the Acquirer may
disclose Confidential Information (i) to its attorneys, accountants, consultants and other professionals to the extent necessary to obtain their services in connection with monitoring its 

15

 

investment
in MWE and who agree to abide by, or are otherwise bound by obligations of confidentiality sufficient to ensure compliance with, this  Section 3.04; provided
further that the Holder Representative shall use commercially reasonable
efforts to limit broad disclosure of such information prior to any election of Holders to exercise rights to include Registered Securities in any Underwritten Offering or to participate in any
Continuous Equity Program or other alternative arrangement under Section 2.04; (ii) to any prospective purchaser of any Registrable
Securities from the Acquirer, if such Holder agrees in writing to become subject to the terms and conditions of the Section 3.04; (iii) to
any existing or prospective Affiliate, partner, member, or wholly-owned subsidiary of the Acquirer in the ordinary course of business and who have a need to know, provided that the Acquirer informs
such Person that such information is confidential and directs such Person to maintain the confidentiality of such information and such Person agrees to abide by, or is otherwise bound by obligations
of confidentiality sufficient to ensure compliance with, this Section 3.04; or (iv) as may otherwise be required by Law, subpoena, civil
investigation, court order, demand or similar legal process, provided that the Acquirer promptly notifies MWE in writing of such disclosure and takes reasonable steps to minimize the extent of such
required disclosure. The Acquirer shall be responsible for any breach of the terms and conditions of this Section 3.04 by any Person described in clause (i), (ii) or
(iii) of the preceding sentence. 

        Section 3.05    Recapitalization, Exchanges, Etc. Affecting the Registrable Securities.    The provisions of
this Agreement shall apply to the fullest extent set forth herein with respect to any and all limited partner interests of MWE or equity securities of any successor or assignee of MWE (whether by
merger, consolidation, sale of assets or otherwise) that may be issued in respect of, in exchange for or in substitution of, the Registrable Securities, and shall be appropriately adjusted for
combinations, splits, recapitalizations and the like occurring after the date of this Agreement. 

        Section 3.06    Specific Performance.    Damages in the event of breach of this Agreement by a party hereto may
be difficult, if not impossible, to ascertain, and it is therefore agreed that each such Person, in addition to and without limiting any other remedy or right it may have, will have the right to an
injunction or other equitable relief in any court of competent jurisdiction, enjoining any such breach, and enforcing specifically the terms and provisions hereof, and each of the parties hereto
hereby waives any and all defenses it may have on the ground of lack of jurisdiction or competence of the court to grant such an injunction or other equitable relief. The existence of this right will
not preclude any such Person from pursuing any other rights and remedies at law or in equity which such Person may have. 

        Section 3.07    Counterparts.    This Agreement may be executed in any number of counterparts and by different
parties hereto in separate counterparts, each of which counterparts, when so executed and delivered, shall be deemed to be an original and all of which counterparts, taken together, shall constitute
but one and the same Agreement. 

        Section 3.08    Applicable Law, Submission to Jurisdiction.    THIS AGREEMENT AND THE RIGHTS OF THE PARTIES
HEREUNDER SHALL BE INTERPRETED IN ACCORDANCE WITH THE LAWS OF THE STATE OF DELAWARE AND ALL RIGHTS AND REMEDIES SHALL BE GOVERNED BY SUCH LAWS WITHOUT REGARD TO PRINCIPLES OF CONFLICT OF LAWS; THE
PARTIES FURTHER AGREE THAT ANY LEGAL ACTION OR PROCEEDING WITH RESPECT TO THIS AGREEMENT OR ANY DOCUMENT RELATING HERETO MAY BE BROUGHT ONLY IN A FEDERAL OR STATE COURT OF COMPETENT JURISDICTION IN
HOUSTON, TEXAS. EACH PARTY HEREBY IRREVOCABLY WAIVES ANY OBJECTION, INCLUDING, BUT NOT LIMITED TO, ANY OBJECTION TO THE LAYING OF VENUE OR BASED ON THE GROUNDS OF FORUM NON-CONVENIENCE,
WHICH IT MAY NOW OR HEREAFTER HAVE TO THE BRINGING OF SUCH ACTION OR PROCEEDING IN ANY SUCH RESPECTIVE JURISDICTION. 

16

 

        Section 3.09    Waiver of Jury Trial.    THE PARTIES TO THIS AGREEMENT EACH HEREBY KNOWINGLY, VOLUNTARILY,
INTENTIONALLY, AND IRREVOCABLY WAIVE, AND AGREE TO CAUSE THEIR AFFILIATES TO WAIVE, TO THE FULLEST EXTENT PERMITTED BY LAW, ANY RIGHT TO TRIAL BY JURY OF ANY CLAIM, DEMAND, ACTION OR CAUSE OF ACTION
(i) ARISING UNDER THIS AGREEMENT OR (ii) IN ANY WAY CONNECTED WITH OR RELATED OR INCIDENTAL TO THE DEALINGS OF THE PARTIES HERETO IN RESPECT OF THIS AGREEMENT OR ANY OF THE TRANSACTIONS
RELATED HERETO, IN EACH CASE WHETHER NOW EXISTING OR HEREAFTER ARISING, AND WHETHER IN CONTRACT, TORT, EQUITY OR OTHERWISE. THE PARTIES TO THIS AGREEMENT EACH HEREBY AGREES AND CONSENTS THAT ANY SUCH
CLAIM, DEMAND, ACTION OR CAUSE OF ACTION SHALL BE DECIDED BY COURT TRIAL WITHOUT A JURY AND THAT THE PARTIES TO THIS AGREEMENT MAY FILE AN ORIGINAL COUNTERPART OF A
COPY OF THIS AGREEMENT WITH ANY COURT AS WRITTEN EVIDENCE OF THE CONSENT OF THE PARTIES HERETO TO THE WAIVER OF THEIR RIGHT TO TRIAL BY JURY. 

        Section 3.10    Severability of Provisions.    Any provision of this Agreement that is prohibited or
unenforceable in any jurisdiction shall, as to such jurisdiction, be ineffective to the extent of such prohibition or unenforceability without invalidating the remaining provisions hereof or affecting
or impairing the validity or enforceability of such provision in any other jurisdiction. 

        Section 3.11    Entire Agreement.    This Agreement is intended by the parties as a final expression of their
agreement and intended to be a complete and exclusive statement of the agreement and understanding of the parties hereto in respect of the subject matter contained herein. There are no restrictions,
promises, warranties or undertakings, other than those set forth or referred to herein with respect to the rights granted by MWE set forth herein. This Agreement supersedes all prior agreements and
understandings between the parties with respect to such subject matter. 

        Section 3.12    Amendment.    This Agreement may be amended only by means of a written amendment signed by MWE
and the Holders of a majority of the then outstanding Registrable Securities; provided, however, that no
such amendment shall disproportionately and adversely affect the rights of any Holder hereunder without the consent of such Holder. 

        Section 3.13    No Presumption.    In the event any claim is made by a party relating to any conflict,
omission, or ambiguity in this Agreement, no presumption or burden of proof or persuasion shall be implied by virtue of the fact that this Agreement was prepared by or at the request of a particular
party or its counsel. 

        Section 3.14    Obligations Limited to Parties to this Agreement.    Each of the parties hereto covenants,
agrees and acknowledges that no Person other than the Acquirer, its permitted assignees and MWE shall have any obligation hereunder and that, notwithstanding that one or more of MWE and the Acquirer
may be a corporation, partnership, limited liability company or other entity, no recourse under this Agreement or under any documents or instruments delivered in connection herewith or therewith shall
be had against any former, current or future director, officer, employee, agent, general or limited partner, manager, member, stockholder or Affiliate of any of MWE, the Acquirer or their respective
permitted assignees, or any former, current or future director, officer, employee, agent, general or limited partner, manager, member, stockholder or Affiliate of any of the foregoing, whether by the
enforcement of any assessment or by any legal or equitable proceeding, or by virtue of any applicable Law, it being expressly agreed and acknowledged that no personal liability whatsoever shall attach
to, be imposed on or otherwise by incurred by any former, current or future director, officer, employee, agent, general or limited partner, manager, member, stockholder or Affiliate of any of MWE, the
Acquirer or any of their respective assignees, or any former, current or future director, officer, employee, agent, general or limited partner, manager, member, stockholder or Affiliate of any of the
foregoing, as such, for any obligations of MWE, the Acquirer or their respective permitted assignees under this Agreement or any documents or instruments delivered in connection herewith or therewith
or for any claim based on, in respect of or by reason of such obligation or its creation, except in each case for any assignee of a Holder. 

[Signature Page Follows] 

17

        IN
WITNESS WHEREOF, the parties hereto execute this Agreement, effective as of the date first above written. 

 

					
	 	 	MARKWEST ENERGY PARTNERS, L.P.
	

 	
 	
 By:	
 	

MarkWest Energy GP, L.L.C.,

its general partner
	

 	
 	
By:	
 	
/s/ Frank M. Semple

 
	 	 	Name:	 	Frank M. Semple

 
	 	 	Title:	 	President and CEO

 

 

   

   

SIGNATURE PAGE TO

REGISTRATION RIGHTS AGREEMENT

 

					
	 	 	M&R MWE LIBERTY, LLC
	

 	
 	

 	
 	

 
	 	 	By:	 	/s/ John T. Raymond

 
	 	 	Name:	 	John T. Raymond

 
	 	 	Title:	 	CEO & Managing Partner

 

 

   

   

 SIGNATURE PAGE TO

REGISTRATION RIGHTS AGREEMENT

QuickLinks

TABLE OF CONTENTS

REGISTRATION RIGHTS AGREEMENT

ARTICLE I DEFINITIONS

ARTICLE II REGISTRATION RIGHTS

ARTICLE III MISCELLANEOUSQuickLinks
 -- Click here to rapidly navigate through this document

 

 
 

  Exhibit 10.33    
    

SPECIFIC TERMS IN THIS EXHIBIT HAVE BEEN REDACTED BECAUSE CONFIDENTIAL TREATMENT FOR THOSE TERMS HAS BEEN REQUESTED. THE REDACTED MATERIAL HAS BEEN SEPERATELY FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION, AND THE TERMS HAVE BEEN MARKED AT THE APPROPRIATE PLACE WITH TWO ASTERISKS (**).

 
 

  AMENDMENT NO. 3 TO
  SECOND AMENDED AND RESTATED LIMITED LIABILITY COMPANY
  AGREEMENT OF MARKWEST LIBERTY MIDSTREAM & RESOURCES, L.L.C.    
    

        This Amendment No. 3 dated December 19, 2011 (this "Amendment") to the
Second Amended and Restated Limited Liability Company Agreement of MarkWest Liberty Midstream & Resources, L.L.C., dated as of November 1, 2009, as amended by that certain Amendment
No. 1, dated as of November 20, 2009, and that certain Amendment No. 2, dated as of April 28, 2011 (as so amended and as further amended from time to time, the
"Agreement"), is made and entered into by the Company and the undersigned Members of the Company, and hereby amends the Agreement as set forth herein.
Capitalized terms not otherwise defined herein shall have the meaning in the Agreement. 

        WHEREAS,
the Members have never intended for a Transfer of Interests from the NGPMR Group to the MWE Liberty Group to be considered an NGPMR Exit Transaction or a Partial NGPMR Exit
Transaction; and 

        WHEREAS,
pursuant to that unanimous written consent of the Managers and Members dated the date hereof, the Board and the Members have consented to this Amendment; and 

        WHEREAS,
the undersigned are the sole Members of the Company and pursuant to Section 15.9 of the Agreement, the Members and the Company desire to amend the Agreement to modify the
Agreement in the manner set forth in this Amendment; 

        NOW
THEREFORE, in consideration of the mutual promises made herein, the parties, intending to be legally bound, hereby agree as follows: 

        1.     Section 5.6
of the Agreement is hereby amended by deleting the first paragraph thereof and replacing it with the following: 

        "In
the event NGPMR receives cash from any NGPMR Exit Transaction or Partial NGPMR Exit Transaction, in each case other than such a transaction that consists of a Transfer of Interests
by the NGPMR Group to the MWE Liberty Group (for the purposes of this section, such transaction an "Incentive Interest Transaction") that would result
in ** Payout**, simultaneously with the consummation of any such transaction, NGPMR shall pay to MWE
Liberty as a fee the following amount**, to the extent applicable:" 

        2.     Section 7.2
of the Agreement is hereby amended to add Section 7.2(a)(iii) as follows: 

        "(iii)  For
the avoidance of doubt, for purposes of this Section 7.2(a), if any member of the NGPMR Group is a Transferring Member, a Third Party Offer to such member
of the NGPMR Group for a ROFO Interest will not constitute a Qualifying Third Party Offer if the consideration that would be received by such member of the NGPMR Group for such ROFO Interest pursuant
to such Third Party Offer, net of any amount** that would be required to be paid to MWE Liberty pursuant to Section 5.6 as a result of the
Transfer of such ROFO Interest to the third party making such Third Party Offer, does not exceed the consideration payable to such member of the NGPMR Group for such ROFO Interest pursuant to any ROFO
Offer made by any member or members of the MWE Liberty Group." 

        3.     Except
as hereby expressly modified by this Amendment, all terms of the Agreement remain in full force and effect. This Amendment shall bind and benefit the Company and
its Members and their respective heirs, beneficiaries, administrators, executors, receivers, trustees, successors and assigns. 

 

        4.     The
Members agree that the actions of the Board, Members and officers previously taken in connection with the actions, elections and transactions of the Company and
contemplated to be taken under this Amendment and the Consent are in all respects, authorized, approved, ratified and confirmed as the acts and deeds of the Company. 

        5.     This
Amendment may be executed in any number of counterparts, including by electronic transmission, with each such counterpart constituting an original and all of such
counterparts constituting but one and the same instrument. 

[SIGNATURE
PAGE FOLLOWS] 

2

 

        IN
WITNESS WHEREOF, the Company and the Members have executed this Amendment as of the date first written above pursuant to and in accordance with Section 15.9 of the Agreement. 

							
	 COMPANY:	 	 	 	 
	
MARKWEST LIBERTY MIDSTREAM & RESOURCES, L.L.C.,

a Delaware limited liability company	
 	

 	
 	

 
	
 By:	
 	
/s/ Frank M. Semple

 	
 	

 	
 	

 
	Name:	 	Frank M. Semple	 	 	 	 
	Title:	 	President and CEO	 	 	 	 
	
MEMBERS:	
 	

 	
 	

 
	
MARKWEST LIBERTY GAS GATHERING, L.L.C.,

a Delaware limited liability company	
 	
 M&R MWE LIBERTY, LLC,
 a Delaware limited liability company
	
 By:	
 	
/s/ Frank M. Semple

 	
 	
By:	
 	
/s/ John T. Raymond

 
	Name:	 	Frank M. Semple	 	Name:	 	John T. Raymond
	Title:	 	President and CEO	 	Title:	 	Managing Partner & CEO

   

   

 SIGNATURE
PAGE TO

AMENDMENT NO. 3 TO

SECOND AMENDED AND RESTATED LIMITED LIABILITY COMPANY

AGREEMENT OF MARKWEST LIBERTY MIDSTREAM & RESOURCES, L.L.C. 

QuickLinks

Exhibit 10.33

AMENDMENT NO. 3 TO SECOND AMENDED AND RESTATED LIMITED LIABILITY COMPANY AGREEMENT OF MARKWEST LIBERTY MIDSTREAM & RESOURCES, L.L.C.

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