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                                                                    EXHIBIT 10.3

                               AMENDMENT NO. 1 TO

                     MASTER PROFESSIONAL SERVICES AGREEMENT

      This Amendment No. 1 (this "AMENDMENT") to the Master Professional
Services Agreement between The Williams Companies, Inc. ("WILLIAMS") and
International Business Machines Corporation ("PROVIDER") dated June 1, 2004 (the
"AGREEMENT") is made as of June 1, 2004 (the "AMENDMENT EFFECTIVE DATE") by and
between Williams and IBM.

      WHEREAS, Williams and Provider engaged in extensive negotiations,
discussions and due diligence that have culminated in the formation of the
contractual relationship described in the Agreement;

      WHEREAS Williams and Provider desire to make minor changes and corrections
to the Agreement and the various Schedules thereto in order to better reflect
the intended relationship between the parties; and

      WHEREAS, capitalized terms used herein and not otherwise defined herein,
shall have the meanings given such terms in the Agreement,

      NOW THEREFORE, in consideration of good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, Williams and Provider
hereby agree as follows:

1.    OTHER PROVISIONS UNCHANGED. Except as specifically amended hereby, all
      other provisions of the Agreement shall remain in full force and effect.

2.    SECTION 2.1(86). Section 2.1(86) of the Agreement is hereby revised and
      restated to read as follows:

"TAX AUTHORITY" shall mean any federal, state, provincial, regional,
territorial, local or other fiscal, revenue, customs or excise authority, body
or official competent to impose, collect or assess tax.

3. SECTION 16.1(c). The first sentence of Section 16.1(c) of the Agreement is
hereby revised and restated to read as follows:

      "ENDORSEMENTS. Provider's insurance policies as required herein under
      Sections 16.1(a)(ii) and (iii) shall name Williams, Williams Affiliates
      and Eligible Recipients and their respective officers, directors and
      employees as Additional Insureds for any and all liability arising at any
      time in connection with Provider's performance under this Agreement."

4.    SECTION 9.1(a). The first sentence of Section 9.1(a) of the Agreement is
      hereby revised and restated to read as follows:

                                       1

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      DELIVERY AND CONTENTS. As part of the Services, and at no additional cost
      to Williams, Provider shall deliver to Williams for its review, comment
      and approval (i) a reasonably complete draft of the Policy and Procedures
      Manual by the date indicated in Schedule H and (ii) a final draft of the
      Policy and Procedures Manual by the date indicated in Schedule H or, if
      later, within thirty (30) days after receipt of comments and suggestions
      as described in Section 9.1(b).

      In Section 9.1(a)(iii), the words "and 15.14" are deleted.

5. SECTION 12.2. The final sentence of Section 12.2 of the Agreement is hereby
revised and restated to read as follows:

"Prior to the Commencement Date and until such time Williams achieves an
investment grade status of Moody's "Baa3" or better, or Standard & Poors "BBB-"
or better, Williams shall provide to Provider an irrevocable letter of credit of
Two Million Dollars ($2,000,000) to the benefit of Provider to be drawn upon by
Provider in its sole discretion in the event of Williams's non-payment of
undisputed amounts after first giving notice to Williams and providing Williams
the five (5) business day opportunity to cure as set forth above."

6. Section 18.3(c)(i). The word "indemnitees" is replaced by "indemnities."

7. Section 21.3(a): The address under the second heading of "with a copy to" is
replaced by the following:

      General Counsel
      IBM Business Consulting Services
      Building 2, Route 100
      Somers, NY 10589

8.    SCHEDULE B. Schedule B is hereby replaced with the revised Schedule B
      attached to the Agreement.

9.    SCHEDULE D. Schedule D is hereby amended as set forth in Exhibit 1 hereto

10.   SCHEDULE G. Schedule G and the Attachments to Schedule G are hereby
      replaced with the revised Schedule G and the revised Attachments to
      Schedule G attached to the Agreement.

11.   SCHEDULE J. Schedule J and the Attachments to Schedule J are hereby
      replaced with the revised Schedule J and the revised Attachments to
      Schedule J attached to the Agreement.

12.   SCHEDULE L. Schedule L is hereby replaced with the revised Schedule L
      attached to the Agreement.

13.   SCHEDULE S. Schedule S is hereby amended as set forth in Exhibit 1 hereto.

                                       2

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10.   COUNTERPARTS. This Amendment may be executed in more than one counterparts
      by the parties hereto, each of which shall be deemed an original but all
      of which shall constitute one and the same instrument.

11.   GOVERNING LAW AND FORUM. This Amendment and performance under it shall be
      governed by and construed in accordance with Section 19.5 of the
      Agreement. This Amendment is incorporated into and made a part of the
      Agreement. This Amendment is subject to the terms and conditions of the
      Agreement, as such terms are modified by this Amendment.

                                       3

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      IN WITNESS WHEREOF, the parties have caused this Amendment to be executed
by their respective duly authorized representatives as of the Amendment
Effective Date.

THE WILLIAMS COMPANIES, INC.                INTERNATIONAL BUSINESS
                                            MACHINES CORPORATION

By:  /s/ Michael P. Johnson                 By: /s/ Edward V. Kelly
     ----------------------------------         --------------------------------
Title: Senior Vice President                Title:  Senior Project Executive
Date 08/02/04                               Date: 08/02/04

                                      S-1<PAGE>

                                                                    EXHIBIT 10.4

                                 AMENDMENT NO.2

                                       to

                               PURCHASE AGREEMENT,

                           dated as of April 18, 2003,

                                  by and among

                         WILLIAMS ENERGY SERVICES, LLC,

                     WILLIAMS NATURAL GAS LIQUIDS, INC. and

                                 WILLIAMS GP LLC

                        collectively, as Selling Parties,

                                       and

                             WEG ACQUISITIONS, L.P.
                         a Delaware limited partnership,
                                    as Buyer,

                          for the purchase and sale of

                       (i) all the membership interests of

                                   WEG GP LLC
                      a Delaware limited liability company,

             (ii) all of the Common Units and Subordinated Units of

                          WILLIAMS ENERGY PARTNERS L.P.
                         a Delaware limited partnership

  owned by Williams Energy Services, LLC and Williams Natural Gas Liquids, Inc.

                                       and

                      (iii) all the Class B Common Units of

                          WILLIAMS ENERGY PARTNERS L.P.
                         a Delaware limited partnership

                           dated as of January 6, 2004

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                                 AMENDMENT NO. 2

                                       TO

                               PURCHASE AGREEMENT

      THIS AMENDMENT NO. 2 TO PURCHASE AGREEMENT (THIS "AMENDMENT NO. 2") is
made and entered into as of this 6th day of January 2004, by and among WILLIAMS
ENERGY SERVICES, LLC, a Delaware limited liability company ("WES"), WILLIAMS
NATURAL GAS LIQUIDS, INC., a Delaware corporation ("WNGL"), and WILLIAMS GP LLC,
a Delaware limited liability company (the "OLD COMPANY," and collectively with
WES and WNGL, the "SELLING PARTIES"), and MAGELLAN MIDSTREAM HOLDINGS, L.P.,
formerly WEG Acquisitions, L.P., a Delaware limited partnership ("BUYER").

                                   WITNESSETH:

      WHEREAS, the Selling Parties and Buyer entered into the Purchase
Agreement, dated as of April 18, 2003 (the "PURCHASE AGREEMENT"), pursuant to
which, on the terms and subject to the conditions set forth therein, the Selling
Parties sold, and Buyer purchased, at the Closing the Securities (as such terms
are defined in the Purchase Agreement); and

      WHEREAS, in accordance with Section 9.8 of the Purchase Agreement, the
Selling Parties and Buyer have agreed to enter into this Amendment No. 2 to
amend the Purchase Agreement to the extent, and only to the extent, specified
below;

      NOW, THEREFORE, in consideration of the mutual terms, conditions and other
agreements set forth herein and in the Purchase Agreement, the parties hereto
agree as follows:

                                    ARTICLE I
                                   AMENDMENTS

      SECTION 1.1. AMENDMENT. The Purchase Agreement is hereby amended by
deleting Schedule 1.3 attached thereto and replacing it with Schedule 1.3
attached to this Amendment No. 2.

                                   ARTICLE II
                                  MISCELLANEOUS

      SECTION 2.1. SIGNATURES AND COUNTERPARTS. Facsimile transmissions of any
signed original document and/or retransmission of any signed facsimile
transmission shall be the same as delivery of an original. At the request of
Buyer or the Selling Parties, the parties will confirm facsimile transmission by
signing a duplicate original document. This Amendment No. 2 may be executed in
two or more counterparts, each of which shall be deemed an original and all of
which together shall be considered one and the same document.

      SECTION 2.2. GOVERNING LAW. This Amendment No. 2 shall be governed by and
construed in accordance with the internal and substantive laws of New York and
without regard to any conflicts of laws concepts that would apply the
substantive law of some other jurisdiction.

      SECTION 2.3. CONTINUATION OF PURCHASE AGREEMENT. To the extent not amended
hereby, the Purchase Agreement shall remain in full force and effect.

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      IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 2
as of the date first above written.

SELLING PARTIES:            WILLIAMS ENERGY SERVICES, LLC

                            By:     /s/ Travis N. Campbell
                                 ----------------------------------
                            Name:  Travis N. Campbell
                            Title: Treasurer

                            WILLIAMS NATURAL GAS LIQUIDS, INC.

                            By:     /s/ Travis N. Campbell
                                 -----------------------------------
                            Name:  Travis N. Campbell
                            Title: Treasurer

                            WILLIAMS GP LLC

                            By:  WILLIAMS ENERGY SERVICES, LLC and
                                 WILLIAMS NATURAL GAS LIQUIDS, INC.,
                                 Its Members

BUYER:                      MAGELLAN MIDSTREAM HOLDINGS, L.P.

                            By:  MAGELLAN MIDSTREAM MANAGEMENT, LLC
                                 It General Partner

                            By:     /s/ Don R. Wellendorf
                                 -----------------------------------
                            Name:  Don R. Wellendorf

                            Title: President and CEO

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