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                                                                     EXHIBIT 5.1

                             ANDREWS & KURTH L.L.P.

                             600 Travis, Suite 4200
                                Houston, TX 77002




March 21, 2001



The Williams Companies, Inc.
One Williams Center
Tulsa, Oklahoma 74172

Ladies and Gentlemen:

         We have acted as counsel for The Williams Companies, Inc., a Delaware
corporation (the "Company"), in connection with the filing by the Company with
the Securities and Exchange Commission of a Registration Statement on Form S-4
(the "Registration Statement") with respect to (i) the issuance by the Company
of up to $700,000,000 aggregate amount of its 7.50% Debentures due January 15,
2031, Series A (the "Exchange Debentures"), registered pursuant to the
Registration Statement under the Securities Act of 1933, as amended (the
"Securities Act"), in exchange for up to $700,000,000 aggregate amount of the
Company's outstanding 7.50% Debentures due January 15, 2031 (the "Outstanding
Debentures") and (ii) the issuance by the Company of up to $400,000,000
aggregate amount of its 6.75% Putable Asset Term Securities (PATS)
Putable/Callable January 15, 2006, Series A (the "Exchange PATS"), registered
pursuant to the Registration Statement under the Securities Act, in exchange for
up to $400,000,000 aggregate amount of the Company's outstanding 6.75% Putable
Asset Term Securities (PATS) Putable/Callable January 15, 2006 (the "Outstanding
PATS"). The Exchange Debentures are to be issued pursuant to an Indenture dated
as of November 10, 1997 (the "Original Indenture"), as amended by the Fifth
Supplemental Indenture dated as of January 17, 2001 (collectively, the
"Debenture Indenture") between the Company and Bank One Trust Company, N.A., as
Trustee. The Exchange PATS are to be issued pursuant to the Original Indenture,
as amended by the Fourth Supplemental Indenture dated as of January 17, 2001
(collectively, the "PATS Indenture") between the Company and Bank One Trust
Company, N.A., as Trustee.

         Before rendering our opinions hereinafter set forth, we examined such
certificates, instruments and records of the Company, including the Debenture
Indenture and the PATS Indenture, and we reviewed such questions of law, as we
considered appropriate. Unless otherwise specified, capitalized terms used and
not defined herein shall have the meaning assigned to them in the Original
Indenture.

         Based upon the foregoing, we are of the opinion that:

         (i) When the Registration Statement has become effective under the
Securities Act and the Exchange Debentures have been duly executed and
authenticated in accordance with the
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                                                                     EXHIBIT 5.1


Debenture Indenture and issued as contemplated in the Registration Statement,
the Exchange Debentures will constitute valid and legally binding obligations of
the Company, subject to bankruptcy, insolvency, reorganization, moratorium and
other laws relating to or affecting creditors' rights generally and to general
equitable principles.

         (ii) When the Registration Statement has become effective under the
Securities Act and the Exchange PATS have been duly executed and authenticated
in accordance with the PATS Indenture and issued as contemplated in the
Registration Statement, the Exchange PATS will constitute valid and legally
binding obligations of the Company, subject to bankruptcy, insolvency,
reorganization, moratorium and other laws relating to or affecting creditors'
rights generally and to general equitable principles.

         In rendering the opinion expressed above, with your consent and without
independent investigation or verification of any kind, we have also assumed the
following: (i) each of the parties to the Exchange Debentures, the Exchange
PATS, the Debenture Indenture and the PATS Indenture (collectively, the
"Transaction Documents") has been duly formed or incorporated (as applicable),
is validly existing and is in good standing under the laws of the jurisdiction
of its formation or incorporation (as applicable), and is qualified to do
business in each jurisdiction in which such qualification is required; (ii) each
of the parties to the Transaction Documents has the power and authority and full
legal right to execute and deliver each of the Transaction Documents to which it
is a party, and to perform its obligations thereunder; (iii) the execution,
delivery and performance of the Transaction Documents by the parties thereto
have been duly authorized by all requisite action on the part of each such
Person; (iv) each party to the Transaction Documents has the power, authority
and full legal right to execute, deliver and perform the Transaction Documents
to which it is a party; (v) the Transaction Documents have been duly executed
and delivered by each of the parties thereto; and (vi) each Transaction Document
is the legal, valid and binding obligation of each party thereto (other than
Company), enforceable against such other party in accordance with its terms.

         The enforceability of the rights to exculpation, indemnity and
contribution provided in the Transaction Documents may be limited by (i) laws
rendering unenforceable indemnification provisions that are contrary to Federal
or state securities laws and the public policy underlying such laws, (ii) laws
limiting the enforceability of provisions exculpating or exempting a Person
from, or requiring indemnification or limiting the liability of a Person for (A)
its own action or inaction, to the extent such action or inaction involves gross
negligence, recklessness or willful or unlawful conduct or (B) any obligation
which has not been disclosed to the Person providing such indemnity, exemption
or exculpation and is not reasonably within the scope of such provisions or the
overall intention of the parties at the time of the execution of such
Transaction Documents.

         The foregoing opinions are limited to the laws of the State of New York
and the United States of America, in each case in existence as of the date
hereof and we do not express any opinion as to the laws of any other
jurisdiction.

         We hereby consent to the statements made with respect to us under the
caption "United States Federal Tax Considerations" and "Legal Matters" in the
prospectus contained in
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                                                                     EXHIBIT 5.1


the Registration Statement and to the filing of this opinion as an exhibit to
the Registration Statement. By giving such consent, we do not admit that we are
within the category of persons whose consent is required under Section 7 of the
Securities Act or the rules and regulations of the Commission issued thereunder.

                                                   Very truly yours,

                                                   /s/ ANDREWS & KURTH L.L.P.