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 (**).

NATAURAL
GAS LIQUIDS PURCHASE AGREEMENT

By
and Between

ONEOK
HYDROCARBON, L.P.

and

MARKWEST
WESTERN OKLAHOMA GAS COMPANY, L.L.C.

Dated:
August 25, 2006

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TABLE OF CONTENTS

Section, Description

Page #Section 1., Definitions

1Section 2., Term

3Section 3., Delivery by Seller, Acceptance by Buyer

3Section 3.A., Quantity

3Section 3.B., Change in Operations

4Section 3.C., Deliveries

4Section 3.D., Quality

5Section 3.E., Marketing Agreements

5Section 4., Purchase of NGL's

5Section 5., Linefill

6Section 6., Base and Adjusted Differential

6Section 7., Quality Adjustment Fees

7Section 8., Alternative Connections

8Section 9., Payments, Taxes

8Section 10., Credit

10Section 11., Measurement, Sampling and Analysis

10Section 12., Records

13Section 13., Custody and Title

13Section 14., Warranties

13Section 15., Indemnifications

14Section 16., Defaults

14Section 17., Excuse of Performance

15Section 18., Assignment

16Section 19., Notices

16Section 20., Interpretation

17Section 21., Confidentiality

18Section 22., Amendments

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NATURAL GAS LIOUIDS PURCHASE AGREEMENT

This Natural Gas Liquids Purchase Agreement ("Agreement") is made on this 29 Day of August, 2006, by and between MarkWest Western
Oklahoma Gas Company, L.L.C., an Oklahoma limited liability company, ("Seller"), and ONEOK Hydrocarbon, L.P., a Delaware limited partnership, ("Buyer"). Buyer and Seller may be referred to
herein as a "Party", or collectively as "Parties" .

WHEREAS,Seller or its Affiliates (defined below) are in the business of producing and marketing NGL's (defined below), and
Owns or Controls certain raw natural gas liquid production from Seller's Arapaho gas processing plant in Custer County, Oklahoma (hereinafter referred to as the "Plant"); and

WHEREAS,Seller wishes to sell to Buyer all NGL's extracted at the Plant which are Owned or Controlled by Seller; and

WHEREAS,Buyer wishes to purchase such NGL's pursuant to the terms and conditions hereinafter set forth..

NOW, THEREFORE,in consideration of the mutual covenants and promises herein contained, and other good and valuable consideration, Seller
and Buyer agree as follows:

1.Definitions.In this Agreement, each of the following terms shall have the
meanings assigned as follows:

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2

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2.Term.This Agreement shall begin on the Effective Date, and shall be
effective until**(the "Original Contract Term"). This Agreement shall continue in effect**

**
unless either Party gives the other Party written notice of termination at least**prior to the end of the Original Contract Term or the end of any
subsequent**.

3.Delivery by Seller, Acceptance by Buyer.



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4

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4.Purchase of NGL's.

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5.Linefill

6.Base and Adjusted Base Differential.For each Gallon of purity products
which will be fractionated from the NGL's delivered to Buyer at the Delivery Point as determined by Buyer's measurement and analysis, Seller shall pay Buyer a purchase differential as
set forth in the table below ("Base Purchase Differential"), as adjusted pursuant to the following provisions of this Section. Such Base Differential

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(as
adjusted) shall be charged Seller by Buyer upon receipt of NGL's at the Delivery Point and shall be deducted from the purchase price of the NGL's in accordance with
Section 4.b.

Product

Base Purchase Differential
¢/Gal.Propane Plus

**Ethane in E/P

**


7.Quality Adjustment Fees.In addition to the Adjusted Base Differential
specified above, Seller shall pay Buyer the quality adjustment fees specified below.

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CO2 Content

CO2 Quality Adjustment Fee, per Barrel
of NGL's delivered hereunder**

**


8.Alternative Connections.    Notwithstanding anything to the contrary contained
herein, if the Plant is shut down or the natural gas and NGL's previously being processed in the Plant are diverted to another gas plant(s), Buyer (or its Affiliate) shall have the
right, at its option, to connect the other gas plant(s) at issue in order to receive the NGL's Seller or its Affiliates Own or Control that would have otherwise been extracted at the
Plant. In the event of such a diversion, Seller shall, within thirty (30) Days prior to such diversion, notify Buyer of the diversion. If Buyer wishes to exercise its option, it shall so notify
Seller, within thirty (30) Days of its receipt of Seller's notice, of Buyer's intent (or its Affiliate's) to so connect to the new gas plant(s), and thereafter shall, at Buyer's (or its
Affiliate's) own cost and expense, connect the new gas plant(s) as soon as is reasonably practicable. Upon such connection, the NGL's Owned or Controlled by Seller or its Affiliates
which are produced at such new gas plant(s) and which were diverted from the Plant shall be delivered under the terms and conditions of this Agreement, and the interconnection between Buyer's, or its
Affiliate's, facilities and the new gas plant's facilities shall be deemed an additional Delivery Point under this Agreement. If Buyer (or its Affiliate) does not so elect to connect the new gas
plant(s), then the NGL's Owned or Controlled by Seller or its Affiliates which are produced at such new gas plant(s) shall be released from this Agreement. Provided, however,
NGL's which are diverted to another gas plant which is connected and flowing NGL's to Buyer or its Affiliate may continue to be delivered hereunder pursuant to the terms
and conditions of this Agreement, at Buyer's option.

9.Payments, Taxes.

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10.Credit.

11.Measurement. Sampling and Analysis.The measurement systems used to
measure NGL's delivered hereunder shall be designed, installed and operated by Buyer or Buyer's designee, at Buyer's expense; however, Seller, at Seller's cost and expense, shall
provide any necessary electrical power to Buyer's building to operate such meter, sampler and any other concomitant equipment. Buyer shall, insofar as Seller has the right to convey such rights, have
a license and servitude on any leasehold or premises of Seller for installing, operating, and maintaining equipment necessary or reasonably desirable for Buyer to perform measurement services
hereunder, with the right to remove the same before or within a reasonable time after the termination or expiration of this Agreement.

10

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11

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(i).

By correcting the error if the percentage of error is ascertainable by calibration test or calculation.(ii).

By using measurements from accurate check meters that have been tested in accordance with this Agreement and were in operation during the period to be corrected.(iii).

By any other method agreed upon by both Parties.




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12.Records.    Each Party shall retain all accounting records and documents
related to this Agreement and prepared by such Party for a period of not less than two (2) Years after the origination date of the document.

13.Custody and Title.    Possession, title, and risk of loss to the
NGL's shall pass from Seller to Buyer and vest in Buyer at the inlet flange connection at the Delivery Point. Upon receipt of the NGL's. Buyer will be deemed to have
exclusive ownership and control of said NGL's and shall be responsible for any injuries or damages caused thereby, except to the extent such injuries or damages are caused by the
actions or omissions of Seller and/or its agents.

14.Warranties.    Seller warrants merchantable title to the NGL's
delivered to Buyer hereunder and the right to sell the same, and further warrants that all such NGL's are, at the time of delivery, free from all charges, liens, encumbrances, defects,
taxes, charges and adverse claims.EXCEPT AS EXPRESSLY WARRANTED HEREIN, INCLUDING WITHOUT LIMITATION THE QUALITY SPECIFICATIONS ESTABLISHED PURSUANT TO SECTION 3.D.,
THERE ARE NO OTHER WARRANTIES, AND IT IS EXPRESSLY AGREED THAT SELLER MAKES NO WARRANTY, EXPRESSED OR IMPLIED, AS TO THE MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE OF THE PRODUCTS TO BE
DELIVERED UNDER THIS AGREEMENT OR AS TO THE RESULTS TO BE OBTAINED FROM THE USE OF SUCH PRODUCTS.Neither Party shall be liable for any incidental, special, indirect,
consequential, exemplary or punitive damages, or damages for loss of profits or revenue, incurred by either Party or any third party, whether in an action in contract or tort (including negligence),
statutory, or otherwise, even if the other Party or any other person has been advised of the possibility of such damages. The limitation of liability provisions provided for herein shall survive any
termination of the Agreement.Seller agrees to indemnify and hold Buyer harmless from and against any and all claims, causes of action, judgments or liabilities brought by or
awarded to third parties arising out of or connected witb any allegation that Seller or its Affiliates did not have title or the authority to sell and convey merchantable title to the same. Said
indemnity includes payments of attorney's fees and expenses incurred in defense of said claims or causes of action. Said indemnity shall survive the expiration or termination of this
Agreement.

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15.Indemnification.Except as otherwise provided for
in this Agreement, Seller and Buyer each assume liability for and shall indemnify, defend and hold harmless the other Party, and that Party's partners or affiliates, and their officers, employees, and
agents, from and against all liability, loss, claims, strict liability claims, demands, lawsuits, judgments, orders, penalties, expenses (including but not limited to reasonable attorneys' fees),
costs, and causes of action (collectively referred to as "Claims") asserted by any person or entity (including but not limited to the employees of either Seller or Buyer) for personal injury or death,
for compliance with environmental laws, regulations, orders, or guidelines, or for loss or damage to property, arising from or relating to, or claimed to arise from or relate to, the activities of the
indemnifying Party pursuant to this Agreement, to the extent that such Claims are caused by tbe negligence or willful misconduct of the indemnifying Party or its agents, employees or
contractors.

16.Defaults.

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17.Excuse of Performance.

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18.Assignment.The rights and obligations of this Agreement shall bind and
inure to the respective successors and assigns of the Parties hereto. However, any assignment or attempted assignment, except to an Affiliate, shall be void without the prior written consent of the
other Party, which consent shall not be unreasonably withheld, conditioned, delayed or denied except for reasons which may include, but not be limited to the creditworthiness of the assignee. Seller
further agrees that it and its Affiliates will not sell or assign their interest in the NGL's subject to this Agreement or in the Plant unless (i) contemporaneously with such
sale or assignment, this Agreement is assigned to such assignee; and (ii) the buyer or assignee agrees, in a writing executed by an authorized representative of the buyer or assignee and
delivered to Buyer, that it and the NGL's so sold or assigned shall be bound by, and subject to this Agreement.

18.Notices.Written notices, demands and statements shall be directed as
follows:

General
Notices and writings:

Buyer:

Seller:ONEOK Hydrocarbon, L.P.
P.O. Box 871, MD 2-1
Tulsa, Oklahoma 74103-4298
Attn: Sheridan Swords
Telephone: (918) 588-7010
Fax: (918) 588-7877
E-mail:sheridan.swords@oneok.com

MarkWest Western Oklahoma Gas Company, L.L.C.
1515 Arapahoe Street, Tower 2
Suite 700
Denver, CO 80202
Attn: John Mollenkopf
Telephone: (303) 290-8700
Fax: (303) 290-8769
E-mail: jmollenkopf@tnarkwest.com


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Statements,
Invoices:

Buver:

Seller:ONEOK Hydrocarbon, L.P.
Attn: Brenda Balmer
100 W 5TH STREET
Tulsa, OK 74103

MarkWest Western Oklahoma Gas Company, L.L.C.
1515 Arapahoe Street, Tower 2
Suite 700
Denver, CO 80202
Attn: Accounts Receivable/Accounts Payable
Telephone: (303) 290-8700
Fax: (303) 290-8769
E-mail:


Wire
Payments:

Buver:

Seller:**

**


Notices,
demands, and statements shall be deemed received the Day after the Day of mailing if mailed by United States express or certified mail, return receipt requested, and, in all
other cases, deemed received upon the actual Day of delivery or, if transmitted by facsimile, on the Day the transmission is sent, if sent during normal business hours. Either Party may change its
address shown above by notifying the other Party, in writing, of such change in accordance with this Section.

19.Interpretation.

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20.Confidentiality.Each Party recognizes and acknowledges each Parties'
proprietary interest in this Agreement and each Party agrees to hold in confidence and not to divulge any of the contents hereof or information obtained in association with this Agreement to any other
third party, person, firm, corporation or other entity. Each Party further agrees to be responsible for enforcing the confidentiality of this Agreement and agrees to take such action as necessary to
prevent any disclosure by any of its agents or employees.

21.Amendments.No modification of, addition to, or waiver of any of the terms
of this Agreement shall be binding upon either Party unless in writing and signed by an authorized representative of such Party.

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IN
WITNESS WHEREFORE, the undersigned Parties have executed this Agreement in duplicate originals as of date first set forth above.

Seller:

Buyer:MARKWEST WESTERN OKLAHOMA GAS COMPANY, L.L.C.

ONEOK HYDROCARBON, L.P.By: ONEOK Hydrocarbon GP, L.L.C.,
its general partnerBy:

/s/ Frank Semple

By:

/s/ Sheridan SwordsPrinted Name:

Frank Semple

Printed Name:

Sheridan SwordsTitle:

President

Title:

Vice-President


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EXHIBIT A        SEVERANCE TAX AFFIDAVIT

Check and initial the box next to the statement which applies:



Seller represents that the statement next to the initialed box above is true and correct.

Name:

/s/ John Mollenkopf John Mollenkopf

Date:

8/29/06Title:

SVP


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APPENDIX I  An example of the computations for Fuel Gas and electric power adjustments in Section 6.

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EXHIBIT Y, SPECIFICATIONS, DEMETHANlZED MIX (NGL'S)

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