<PAGE>
                                                                    EXHIBIT 10.2

                      FOURTH AMENDMENT TO CREDIT AGREEMENT

         THIS FOURTH AMENDMENT TO CREDIT AGREEMENT (herein called this
"Amendment"), dated as of March 11, 2002, is entered into by and among The
Williams Companies, Inc., a Delaware corporation, as Borrower pursuant to the
Credit Agreement (as hereinafter defined), the Banks from time to time party to
the Credit Agreement, the Co-Syndication Agents as named therein, the
Co-Documentation Agents as named therein and Citibank, N.A., as agent for the
Banks (in such capacity, the "Agent"). Except as otherwise defined or as the
context requires, terms defined in the Credit Agreement are used herein as
therein defined.

                                   WITNESSETH:

         WHEREAS, The Williams Companies, Inc. ("TWC" or the "Borrower") has
entered into a certain Credit Agreement dated as of July 25, 2000 with the
financial institutions from time to time party thereto (the "Banks"), The Chase
Manhattan Bank and Commerzbank AG, as Co-Syndication Agents, Credit Lyonnais New
York Branch, as Documentation Agent, and Citibank, N.A., as Agent (the "Original
Credit Agreement"), which has been amended by that certain Waiver and First
Amendment to Credit Agreement dated as of January 31, 2001, by that certain
Limited Waiver and Second Amendment to Credit Agreement dated as of July 24,
2001 and by that certain Third Amendment to Credit Agreement dated as of
February 7, 2002 (the Original Credit Agreement, as so amended to the date
hereof, the "Credit Agreement");

         WHEREAS, the Borrower and the Banks now desire to amend the Credit
Agreement in certain respects, as hereinafter provided;

         NOW, THEREFORE, in consideration of the premises and the mutual
agreements herein contained, the Borrower and the Banks hereby agree as follows:

         SECTION 1. Amendment of Section 5.2. Section 5.2 of the Credit
Agreement is hereby amended as follows:

                  (a) Clause (c) of Section 5.2 is hereby amended by deleting
the word "or" at the end of subclause (iv) thereof, deleting the period at the
end of subclause (v) thereof and inserting "; or" in its place, and inserting
the following new subclause (vi) immediately following the existing clause (v):

                  "(vi) Kern River Gas Transmission Company in connection with
         the transaction with a subsidiary of Berkshire Hathaway, Inc. announced
         by TWC on March 7, 2002 from (1) selling, conveying or otherwise
         transferring all or substantially all of its assets or (2) merging or
         consolidating with or into another Person."

         SECTION 2. Representations and Warranties. To induce the Agent and the
Banks to enter into this Amendment, the Borrower hereby reaffirms, as of the
date hereof, its



<PAGE>

representations and warranties contained in Article IV of the Credit Agreement
(except to the extent such representations and warranties relate solely to an
earlier date) and additionally represents and warrants as follows:

                  (a) The Borrower is duly organized, validly existing and in
good standing under the laws of the State of Delaware and has all corporate or
limited liability company powers and all governmental licenses, authorizations,
certificates, consents and approvals required to carry on its business as now
conducted in all material respects, except for those licenses, authorizations,
certificates, consents and approvals which the failure to have could not
reasonably be expected to have a material adverse effect on the business,
assets, condition or operation of the Borrower and its Subsidiaries taken as a
whole. Each material Subsidiary of the Borrower is duly organized or validly
formed, validly existing and (if applicable) in good standing under the laws of
its jurisdiction of incorporation or formation, except where the failure to be
so organized, existing and in good standing could not reasonably be expected to
have a material adverse effect on the business, assets, condition or operations
of the Borrower and its Subsidiaries taken as a whole. Each material Subsidiary
of the Borrower has all corporate or limited liability company powers and all
governmental licenses, authorizations, certificates, consents and approvals
required to carry on its business as now conducted in all material respects,
except for those licenses, authorizations, certificates, consents and approvals
which the failure to have could not reasonably be expected to have a material
adverse effect on the business, assets, condition or operation of the Borrower
and its Subsidiaries taken as a whole.

                  (b) The execution, delivery and performance by the Borrower of
this Amendment and the consummation of the transactions contemplated by this
Amendment are within the Borrower's corporate powers, have been duly authorized
by all necessary corporate action, do not contravene (i) the Borrower's charter
or by-laws or (ii) any law or any contractual restriction binding on or
affecting the Borrower and will not result in or require the creation or
imposition of any Lien.

                  (c) No authorization or approval or other action by, and no
notice to or filing with, any governmental authority or regulatory body is
required for the due execution, delivery and performance by the Borrower of this
Amendment or the consummation of the transactions contemplated by this
Amendment.

                  (d) This Amendment has been duly executed and delivered by the
Borrower. This Amendment and the Credit Agreement as amended by this Amendment
are the legal, valid and binding obligations of the Borrower enforceable against
the Borrower in accordance with its terms, except as such enforceability may be
limited by any applicable bankruptcy, insolvency, reorganization, moratorium or
similar law affecting creditors' rights generally and by general principles of
equity.

                  (e) Except as set forth in the Public Filings and except for
certain class-action lawsuits filed on or after January 29, 2002 alleging fraud
and other violations of applicable securities laws, there is, as to the
Borrower, no pending or, to the knowledge of the Borrower, threatened action or
proceeding affecting the Borrower or any material Subsidiary of the Borrower
before any court, governmental agency or arbitrator, which could reasonably be
expected to materially and adversely affect the financial condition or
operations of the Borrower



                                       2
<PAGE>

and its Subsidiaries taken as a whole or which purports to affect the legality,
validity, binding effect or enforceability of this Amendment, the Credit
Agreement or any Note. For the purposes of this Section, "Public Filings" shall
mean the Borrower's annual report on Form 10-K for the year ended December 31,
2001, and the Borrower's reports on Form 8-K for the period from March 1, 2002
through March 11, 2002.

                  (f) Upon giving effect to this Amendment, no event has
occurred and is continuing which constitutes an Event of Default or which would
constitute an Event of Default but for the requirement that notice be given or
time elapse or both.

         SECTION 3. Conditions to Effectiveness. The effectiveness of this
Amendment is conditioned upon receipt by the Agent of all the following
documents, each in form and substance satisfactory to the Agent:

                  (a) Counterparts of this Amendment executed by the Borrower,
the Agent and Banks constituting not less than the Majority Banks; and

                  (b) Such other documents as the Agent shall have reasonably
requested.

         SECTION 4. Effect. This Amendment shall be deemed to be an amendment to
the Credit Agreement, and the Credit Agreement, as amended hereby, is hereby
ratified, approved and confirmed in each and every respect. All references to
the Credit Agreement in any other document, instrument, agreement or writing
shall hereafter be deemed to refer to the Credit Agreement as amended hereby.

         SECTION 5. Governing Law, Etc. THIS AMENDMENT SHALL BE A CONTRACT MADE
UNDER AND GOVERNED BY THE INTERNAL LAWS OF THE STATE OF NEW YORK (WITHOUT GIVING
EFFECT TO THE PRINCIPLES THEREOF RELATING TO CONFLICT OF LAW EXCEPT SECTION
5-1401 OF THE NEW YORK GENERAL OBLIGATIONS LAW). Whenever possible each
provision of this Amendment shall be interpreted in such manner as to be
effective and valid under applicable law, but if any provision of this Amendment
shall be prohibited by or invalid under applicable law, such provision shall be
ineffective to the extent of such prohibition or invalidity, without
invalidating the remainder of such provision or the remaining provisions of this
Amendment.

         SECTION 6. Counterpart Execution. This Amendment may be executed in any
number of counterparts, all of which taken together shall constitute one and the
same instrument, and any party hereto may execute this Amendment by signing one
or more counterparts.

         SECTION 7. Successors and Assigns. This Amendment shall be binding upon
the Borrower, the Agent and the Banks and their respective successors and
assigns, and shall inure to the benefit of each of the Borrower, the Agent and
the Banks and the successors and assigns of the Banks.



                                       3
<PAGE>

         IN WITNESS WHEREOF, the parties have caused this Amendment to be
executed by their respective officers thereunto duly authorized, to be effective
as of the date first written above.

                                       BORROWER:

                                       THE WILLIAMS COMPANIES, INC.



                                       By: /s/ James G. Ivey
                                          --------------------------------------
                                       Name: James G. Ivey
                                       Title: Treasurer



                                      S-1
<PAGE>

                                       AGENT:

                                       CITIBANK, N.A., as Agent



                                       By: /s/ Lydia G. Junek
                                          --------------------------------------
                                                     Attorney-in-Fact
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------



                                       CO-SYNDICATION AGENTS:

                                       JPMORGAN CHASE BANK
                                       (formerly known as
                                       THE CHASE MANHATTAN BANK),
                                       as Co-Syndication Agent and as a Bank



                                       By: /s/ Signature not legible
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------

                                       COMMERZBANK AG, as Co-Syndication Agent



                                       By: /s/ Harry P. Yergey
                                          --------------------------------------
                                              Senior Vice President & Manager
                                                     Authorized Officer

                                       By: /s/ Brian J. Campbell
                                          --------------------------------------
                                                   Senior Vice President
                                                    Authorized Officer

                                       Date: March 20,2002
                                            ------------------------------------



                                      S-2
<PAGE>

                                       CO-DOCUMENTATION AGENTS:

                                       CREDIT LYONNAIS NEW YORK BRANCH,
                                       as Co-Documentation Agent and as a Bank



                                       By: /s/ Bernard Weymuller
                                          --------------------------------------
                                                   Senior Vice President
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------

                                       BANK OF AMERICA, N.A.
                                       as Co-Documentation Agent and as a Bank



                                       By: /s/ Claire Liu
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-3
<PAGE>

                                       BANKS:

                                       CITIBANK, N.A.



                                       By: /s/ Lydia G. Junek
                                          --------------------------------------
                                                     Attorney-in-Fact
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------



                                      S-4
<PAGE>

                                       THE BANK OF NOVA SCOTIA



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-5
<PAGE>

                                       BANK ONE, N.A. (MAIN OFFICE - CHICAGO)



                                       By: /s/ Janie C. Harman
                                          --------------------------------------
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------



                                      S-6
<PAGE>

                                       COMMERZBANK AG,
                                       NEW YORK AND GRAND CAYMAN BRANCHES


                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-7
<PAGE>

                                       THE FUJI BANK, LIMITED


                                       By: /s/ Jacques Azagury
                                          --------------------------------------
                                                    Authorized Officer

                                       Date: March 15, 2002
                                            ------------------------------------



                                      S-8
<PAGE>

                                       NATIONAL WESTMINSTER BANK PLC
                                       NEW YORK BRANCH



                                       By: /s/ Kevin J. Howard
                                          --------------------------------------
                                       Name: Kevin J. Howard
                                       Title: Managing Director

                                       Date:                              , 2002


                                       NATIONAL WESTMINSTER BANK PLC



                                       BY:
                                          --------------------------------------
                                       NAME:
                                            ------------------------------------
                                       TITLE:
                                             -----------------------------------

                                       DATE:                              , 2002
                                            ------------------------------



                                      S-9
<PAGE>

                                       ABN AMRO BANK, N.V.



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-10
<PAGE>

                                       BANK OF MONTREAL



                                       By: /s/ Signature not legible
                                          --------------------------------------
                                                    Authorized Officer

                                       Date: March 22, 2002
                                            ------------------------------------



                                      S-11
<PAGE>

                                       THE BANK OF NEW YORK



                                       By: /s/ Raymond J. Palmer
                                          --------------------------------------
                                                      Vice President
                                                    Authorized Officer

                                       Date: March 22, 2002
                                            ------------------------------------



                                      S-12
<PAGE>

                                       BARCLAYS BANK PLC



                                       By: /s/ Nicholas A. Bell
                                          --------------------------------------
                                          Director, Loan Transaction Management
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-13
<PAGE>

                                       CIBC INC.



                                       By: /s/ Signature not legible
                                          --------------------------------------
                                                    Authorized Officer

                                       Date: March 20, 2002
                                            ------------------------------------



                                      S-14
<PAGE>

                                       CREDIT SUISSE FIRST BOSTON



                                       By: /s/ James P. Moran
                                          --------------------------------------
                                                         Director
                                                    Authorized Officer

                                       By: /s/ David M. Koczan
                                          --------------------------------------
                                                        Associate
                                                    Authorized Officer

                                       Date: March 19, 2002
                                            ------------------------------------



                                      S-15
<PAGE>

                                       ROYAL BANK OF CANADA



                                       By: /s/ Tom J. Oberaigner
                                          --------------------------------------
                                                      Senior Manager
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------



                                      S-16
<PAGE>

                                       THE BANK OF TOKYO-MITSUBISHI, LTD.,
                                       HOUSTON AGENCY



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-17
<PAGE>

                                       FLEET NATIONAL BANK
                                       f/k/a Bank Boston, N.A.



                                       By: /s/ Signature not legible
                                          --------------------------------------
                                                    Authorized Officer

                                       Date: March 22, 2002
                                            ------------------------------------



                                      S-18
<PAGE>

                                       SOCIETE GENERALE, SOUTHWEST AGENCY



                                       By: /s/ Signature not legible
                                          --------------------------------------
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------



                                      S-19
<PAGE>

                                       THE INDUSTRIAL BANK OF JAPAN, LIMITED,
                                       NEW YORK BRANCH



                                       By: /s/ Michael N. Oakes
                                          --------------------------------------
                                          Senior Vice President, Houston Office
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------



                                      S-20
<PAGE>

                                       TORONTO DOMINION (TEXAS), INC.



                                       By: /s/ Jill Hall
                                          --------------------------------------
                                                      Vice President
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------



                                      S-21
<PAGE>

                                       UBS AG, STAMFORD BRANCH



                                       By: /s/ Patricia O'Kicki
                                          --------------------------------------
                                            Director, Banking Products Services
                                                    Authorized Officer

                                       By: /s/ Wilfred V. Saint
                                          --------------------------------------
                                            Associate Director Banking Products
                                                        Services US
                                                    Authorized Officer

                                       Date: March 20, 2002
                                            ------------------------------------



                                      S-22
<PAGE>

                                       WELLS FARGO BANK TEXAS, N.A.



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-23
<PAGE>

                                       WESTDEUTSCHE LANDESBANK GIROZENTRALE,
                                       NEW YORK BRANCH



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-24
<PAGE>

                                       CREDIT AGRICOLE INDOSUEZ



                                       By: /s/ Mark Lvoff
                                          --------------------------------------
                                           First Vice President, Head of Energy
                                                         Platform
                                                    Authorized Officer

                                       By: /s/ Brian Knezeak
                                          --------------------------------------
                                                   First Vice President
                                                    Authorized Officer


                                       Date: March 22, 2002
                                            ------------------------------------



                                      S-25
<PAGE>

                                       SUNTRUST BANK



                                       By: /s/ Signature not legible
                                          --------------------------------------
                                                    Authorized Officer

                                       Date: March 18, 2002
                                            ------------------------------------



                                      S-26
<PAGE>

                                       THE DAI-ICHI KANGYO BANK, LTD.



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-27
<PAGE>

                                       ARAB BANKING CORPORATION (B.S.C.)



                                       By: /s/ Robert J. Ivosevich
                                          --------------------------------------
                                                  Deputy General Manager
                                                    Authorized Officer

                                       Date: March 22, 2002
                                            ------------------------------------



                                      S-28
<PAGE>

                                       BANK OF CHINA, NEW YORK BRANCH



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-29
<PAGE>

                                       BANK OF OKLAHOMA, N.A.



                                       By: /s/ Robert D. Mattax
                                          --------------------------------------
                                                            SVP
                                                    Authorized Officer

                                       Date: March 15, 2002
                                            ------------------------------------



                                      S-30
<PAGE>

                                       BNP PARIBAS, HOUSTON AGENCY



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-31
<PAGE>

                                       KBC BANK N.V.



                                       By: /s/ Jean-Pierre Diels
                                          --------------------------------------
                                                   First Vice President
                                                    Authorized Officer

                                       By: /s/ Eric Raskin
                                          --------------------------------------
                                                      Vice President
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-32
<PAGE>

                                       SUMITOMO MITSUI BANKING CORPORATION



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-33
<PAGE>

                                       COMMERCE BANK, N.A.



                                       By: /s/ Dennis R. Block,
                                          --------------------------------------
                                                           SVP
                                                    Authorized Officer

                                       Date: March 15, 2002
                                            ------------------------------------



                                      S-34
<PAGE>

                                       RZB FINANCE LLC



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-35
<PAGE>

                                       FIRST UNION NATIONAL BANK



                                       By: /s/ Robert R. Wetteroff,
                                          --------------------------------------
                                                           SVP
                                                    Authorized Officer

                                       Date: March 13, 2002
                                            ------------------------------------



                                      S-36
<PAGE>

                                       UMB BANK, N.A.



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date: _____________________________, 2002



                                      S-37
<PAGE>

                                       MERRILL LYNCH BANK USA



                                       By: /s/ D. Kevin Imlay
                                          --------------------------------------
                                                    Authorized Officer

                                       Date: March 20, 2002
                                            ------------------------------------



                                      S-38
<PAGE>

                                       LEHMAN COMMERCIAL PAPER INC.



                                       By:
                                          --------------------------------------
                                                    Authorized Officer

                                       Date:                              , 2002
                                            ------------------------------



                                      S-39
<PAGE>

                                       NATEXIS BANQUES POPULAIRES


                                       By: /s/ Louis P. Laville, III
                                          --------------------------------------
                                                      Vice President
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------



                                       By: /s/ Daniel Payer
                                          --------------------------------------
                                                      Vice President
                                                    Authorized Officer

                                       Date: March 21, 2002
                                            ------------------------------------



                                      S-40