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                                                              EXHIBIT (e)(6)

                            NONDISCLOSURE AGREEMENT

     THE WILLIAMS COMPANIES, INC., a Delaware corporation ("Williams") and
BARRETT RESOURCES CORPORATION, a Delaware corporation ("Recipient"), sometimes
referred to herein individually as a "Party" and collectively as the "Parties",
in consideration of the mutual covenants of this Agreement, hereby agree as
follows:

1.   Recipient has requested information regarding Williams for the purpose of
     evaluating a possible business combination regarding Williams and Recipient
     ("Transaction"). Williams may consider such information proprietary under
     this Agreement either because it has developed the Information internally,
     or because it has received the Information subject to a continuing
     obligation to maintain the confidentiality of the Information, or because
     of other reasons.

2.   The term "Information" as used in this Agreement shall mean information
     regarding Williams or any of its subsidiaries or their respective assets or
     businesses which is furnished to Recipient by Williams or its
     representatives. Williams shall have the right to determine, in its sole
     judgment, what information it shall provide to Recipient.

3.   With respect to Information disclosed under this Agreement, Recipient
     shall:

     a.   Hold the Information in confidence, exercising a degree of care not
          less than the care used by Recipient to protect its own proprietary or
          confidential information that it does not wish to disclose.

     b.   Restrict disclosure of the Information solely to those directors,
          officers, employees, and/or agents/consultants with a need to know for
          the purpose of evaluating the Transaction and not disclose it to any
          other person.

     c.   Advise those persons to whom the Information was disclosed of their
          obligations with respect to the Information. Recipient shall be
          responsible for any breach of this Agreement by its representatives.

     d.   Use the Information only in connection with continuing discussions by
          the Parties concerning the Transaction, except as may otherwise be
          agreed to by Williams in writing.

4.   The Information shall be deemed the property of Williams and, upon request,
     Recipient shall return all Information received in tangible form to
     Williams, without retaining any copy or duplicate thereof, and shall
     destroy any and all written, printed or other material or information
     derived from the Information and provide Williams written certification of
     such document destruction. If Recipient loses or makes an unauthorized
     disclosure of Williams' Information, it shall notify Williams immediately
     and use reasonable efforts to retrieve the lost or wrongfully disclosed
     Information.

5.   Recipient shall have no obligation to preserve the proprietary nature of
     any Information which:

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     a.   was previously known to Recipient free of any obligation to keep it
          confidential;

     b.   is or becomes publicly available by other than unauthorized
          disclosure;

     c.   is received from a third party whose disclosure, to the best of
          Recipient's knowledge, does not violate any confidentiality
          obligation; or

     d.   is disclosed pursuant to the requirement or request of a governmental
          agency or court of competent jurisdiction to the extent such
          disclosure is required by a valid law, regulation or court order, and
          sufficient notice is given by Recipient to Williams of any such
          requirement or request in order to permit Williams to seek an
          appropriate protective order or exemption from such requirement or
          request.

6.   With respect to any information, including but not limited to Information,
     which Williams discloses to Recipient for the purpose of evaluating the
     Transaction, it is understood and agreed that Williams does not make any
     representations or warranties as to the accuracy, completeness or fitness
     for a particular purpose thereof. It is further understood and agreed that
     neither Williams nor its representatives shall have any liability or
     responsibility to Recipient or to any other person or entity resulting from
     the use of any information so furnished or otherwise provided. Neither this
     Agreement, nor the transfer of Information hereunder, shall be construed as
     granting either expressly, by implication, estoppel, or otherwise, any
     license or right to any information or data now or hereafter owned or
     controlled by Williams to Recipient and all such Information shall remain
     the property of Williams.

7.   Neither this Agreement, nor the disclosure of Information under this
     Agreement, nor the ongoing discussions and correspondence between the
     Parties, shall constitute or imply a commitment or binding obligation
     between the Parties or their respective affiliated companies regarding the
     Transaction. If, in the future, the Parties elect to enter into a binding
     commitment regarding the Transaction, such commitment shall be explicitly
     stated in a separate written agreement executed by both Parties, and the
     Parties hereby affirm that they do not intend their discussions,
     correspondence, and other activities to be construed as forming a contract
     regarding the Transaction or any other transaction between them without
     execution of such separate written agreement.

8.   Recipient acknowledges that it is aware (and that prior to the disclosure
     of any Information to any person pursuant to Paragraph 3b such person will
     be advised) that the United States securities laws prohibit any person who
     has material non-public information about a company from purchasing or
     selling securities of such company or from communicating such information
     to any other person under circumstances in which it is reasonably
     foreseeable that such person is likely to purchase or sell such securities.

9.   This Agreement shall benefit and be binding upon the Parties hereto and
     their respective successors and assigns.

10.  This Agreement shall be governed by and construed in accordance with the
     laws of the State of Oklahoma without regard to choice of law principles.

11.  This Agreement shall become effective as of the date set forth below
     ("Effective Date"). The

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     obligations of the Parties under this Agreement shall survive and continue
     beyond the Effective Date for a period of three (3) years.

12.  Recipient acknowledges that in the event of an unauthorized disclosure, the
     damages incurred by Williams may be difficult if not impossible to
     ascertain, and that Williams may seek injunctive relief as well as monetary
     damages against Recipient for breach of this Agreement.

13.  This Agreement constitutes the entire understanding between the Parties
     with respect to the Information provided hereunder. No amendment or
     modification of this Agreement shall be valid or binding on the Parties
     unless made in writing and executed on behalf of each Party by its duly
     authorized representative.

Each Party represents that it has caused this Agreement to be executed on its
behalf as of the date written below by a representative empowered to bind that
Party with respect to the undertakings and obligations contained herein.

Executed and effective this 6th day of May, 2001

THE WILLIAMS COMPANIES, INC.               BARRETT RESOURCES CORPORATION

By:    /s/ MARK D. WILSON                  By:     /s/ EUGENE A. LANG
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Name:  Mark D. Wilson                      Name:  Eugene A. Lang
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Title: Vice President-Corporate            Title: Executive Vice President,
       Development                                General Counsel and Secretary
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