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                                                                    EXHIBIT 4(p)

                       WILLIAMS HOLDINGS OF DELAWARE, INC.

                          THE WILLIAMS COMPANIES, INC.

                                       AND

                              BANKERS TRUST COMPANY

                          SECOND SUPPLEMENTAL INDENTURE

                            DATED AS OF JULY 31, 1999

             SUPPLEMENTING THE INDENTURE DATED AS OF MARCH 31, 1990
         AND THE FIRST SUPPLEMENTAL INDENTURE DATED AS OF MARCH 31, 1998

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                          SECOND SUPPLEMENTAL INDENTURE

         SECOND SUPPLEMENTAL INDENTURE (the "Second Supplemental Indenture"),
dated as of July 31, 1999, by and among Williams Holdings of Delaware, Inc.
("WHD"), a Delaware corporation, The Williams Companies, Inc. ("TWC"), a
Delaware corporation, and Bankers Trust Company, a New York banking corporation,
as Trustee (the "Trustee").

                                   WITNESSETH:

         WHEREAS, MAPCO Inc. and the Trustee entered into an Indenture dated as
of March 31, 1990 (the "Indenture");

         WHEREAS, MAPCO Inc., WHD, and the Trustee entered into the First
Supplemental Indenture dated as of March 31, 1998 (the "First Supplemental
Indenture");

         WHEREAS, pursuant to an Agreement and Plan of Merger dated as of July
31, 1999, by and among WHD and TWC, WHD has been merged into TWC;

         WHEREAS, Section 9.01 of the Indenture permits WHD and the Trustee to
amend or supplement the Indenture without notice to or the consent of any Holder
of Securities (as defined) to comply with Article Five of the Indenture; and

         WHEREAS, Article Five of the Indenture requires, in the event of a
merger, that the successor expressly assumes by supplemental indenture all of
WHD's obligations in respect of the Indenture.

         NOW, THEREFORE, for and in consideration of the premises and the mutual
covenants contained herein and in the Indenture and for other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged,
WHD, TWC, and the Trustee hereby agree as follows:

         Section 1.  Definitions. Capitalized terms which are used but not
defined herein shall have the meanings ascribed to such terms in the Indenture.

         Section 2.  Assumption of Certain Obligations.

                  (a) TWC hereby expressly assumes (i) the due and punctual
payment of the principal of, premium, if any, on, interest on, and any
additional amounts payable under the Indenture in respect of, the Indenture, and
(ii) the performance of all of the covenants provided for in the Indenture to be
performed or observed by WHD.

                  (b) WHD and the Trustee hereby acknowledge that TWC shall
succeed to, and be substituted for, and may exercise every right and power of,
WHD under the Indenture with the same effect as if TWC had been named therein.

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         Section 3.   Effect of Second Supplemental Indenture. From and after
the execution and delivery of this Second Supplemental Indenture, the Indenture
shall be deemed to be modified as herein provided, but except as modified
hereby, the Indenture shall continue in full force and effect. The Indenture as
modified hereby shall be read, taken, and construed as one and the same
instrument.

         Section 4.   Notice. Any notice or communication by the Trustee to TWC
is duly given if in writing and delivered in person or by express mail service
to the address set forth below:

                           The Williams Companies, Inc.
                           One Williams Center
                           Tulsa, Oklahoma  74172
                           Attention:  Treasurer

         Section 5.   Governing Law. This Second Supplemental Indenture shall be
governed by and construed in accordance with the laws of the State of New York
(regardless of the laws that might otherwise govern under applicable principles
of conflicts of laws) as to all matters, including, without limitation, matters
of validity, construction, effect, performance, and remedies.

         Section 6.   Counterparts. This Second Supplemental Indenture may be
executed in any number of counterparts, each of which, when so executed and
delivered, shall be an original, but such counterparts shall together constitute
but one and the same instrument.

         IN WITNESS WHEREOF, each of WHD, TWC, and the Trustee has caused this
Second Supplemental Indenture to be executed on its behalf by its duly
authorized officer and has caused its official seal to be impressed hereon and
attested by one of its duly authorized officers, all as of the day and year
first above written.

[SEAL]                                      WILLIAMS HOLDINGS OF DELAWARE, INC.

Attest

    /s/  SHAWNA L. GEHRES           By:     /s/ JAMES G. IVEY
-------------------------               ---------------------
Name:    Shawna L. Gehres           Name:   James G. Ivey
Title:   Secretary                  Title:  Treasurer

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[SEAL]                                      THE WILLIAMS COMPANIES, INC.

Attest

     /s/ SHAWNA L. GEHRES           By:     /s/ JAMES G. IVEY
-------------------------               ---------------------
Name:    Shawna L. Gehres           Name:   James G. Ivey
Title:   Secretary                  Title:  Treasurer

[SEAL]                                      BANKERS TRUST COMPANY, AS TRUSTEE

Attest

     /s/ MARC PARILLA                       By:      /s/ SUSAN JOHNSON
---------------------------------               -----------------------------
Name:    Marc Parilla                       Name:    Susan Johnson
Title:   Assistant Vice President           Title:   Assistant Vice President

                                       3<PAGE>   1
                                                                    EXHIBIT 4(q)

                       WILLIAMS HOLDINGS OF DELAWARE, INC.

                          THE WILLIAMS COMPANIES, INC.

                                       AND

                       THE FIRST NATIONAL BANK OF CHICAGO

                                     TRUSTEE

                          FOURTH SUPPLEMENTAL INDENTURE

                            DATED AS OF JULY 31, 1999

                     SUPPLEMENTING THE INDENTURE DATED AS OF
                          FEBRUARY 25, 1997, AS AMENDED

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                          FOURTH SUPPLEMENTAL INDENTURE

         FOURTH SUPPLEMENTAL INDENTURE (the "Fourth Supplemental Indenture"),
dated as of July 31, 1999, by and among Williams Holdings of Delaware, Inc.
("WHD"), a Delaware corporation, The Williams Companies, Inc. ("TWC"), a
Delaware corporation, and The First National Bank of Chicago, a national
banking association, as Trustee (the "Trustee").

                                   WITNESSETH:

         WHEREAS, MAPCO Inc. and the Trustee entered into an Indenture dated as
of February 25, 1997, as amended by a Supplemental Indenture No. 1 dated March
5, 1997, a Supplemental Indenture No. 2 dated March 5, 1997, and a Third
Supplemental Indenture dated March 31, 1998 (the "Indenture"), pursuant to
which Indenture WHD has issued certain 7.25% Notes due 2009 and 7.70%
Debentures due 2027 (collectively, the "Notes"); and

         WHEREAS, pursuant to an Agreement and Plan of Merger dated as of July
31, 1999, by and between WHD and TWC, WHD has been merged into TWC; and

         WHEREAS, Section 8.1 of the Indenture permits the Trustee and WHD to
enter into indentures supplemental to evidence succession of another person to
WHD and the assumption by such successor of the covenants and obligations of
WHD under the Indenture.

         NOW, THEREFORE, for and in consideration of the premises and the
mutual covenants contained herein and in the Indenture and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, WHD, TWC, and the Trustee hereby agree as follows:

         Section 1. Definitions. Capitalized terms, which are used but not
defined herein, shall have the meanings ascribed to such terms in the Indenture.

         Section 2. Assumption of Certain Obligations.

                  (a) TWC hereby expressly assumes (i) the due and punctual
payment of the principal of, premium, if any, on, interest on, and any
additional amounts payable under the Indenture in respect of, the Notes, and
(ii) the performance of all of the covenants provided for in the Indenture to be
performed or observed by WHD.

                  (b) WHD and the Trustee hereby acknowledge that TWC shall
succeed to, and be substituted for, and may exercise every right and power of,
WHD under the Indenture with the same effect as if TWC had been named therein.

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         Section 3. Effect of Fourth Supplemental Indenture. From and after the
execution and delivery of this Fourth Supplemental Indenture, the Indenture
shall be deemed to be modified as herein provided, but except as modified
hereby, the Indenture shall continue in full force and effect. The Indenture as
modified hereby shall be read, taken, and construed as one and the same
instrument.

         Section 4. Notice. Any notice or communication by the Trustee to TWC is
duly given if in writing and delivered in person or by express mail service to
the address set forth below:

                           The Williams Companies, Inc.
                           One Williams Center
                           Tulsa, Oklahoma  74172
                           Attention: Treasurer

         Section 5. Governing Law. This Fourth Supplemental Indenture shall be
governed by and construed in accordance with the laws of the State of New York
(regardless of the laws that might otherwise govern under applicable principles
of conflicts of laws) as to all matters, including, without limitation, matters
of validity, construction, effect, performance, and remedies.

         Section 6. Counterparts. This Fourth Supplemental Indenture may be
executed in any number of counterparts, each of which, when so executed and
delivered, shall be an original, but such counterparts shall together constitute
but one and the same instrument.

         IN WITNESS WHEREOF, each of WHD, TWC, and the Trustee has caused this
Fourth Supplemental Indenture to be executed on its behalf by its duly
authorized officer and has caused its official seal to be impressed hereon and
attested by one of its duly authorized officers, all as of the day and year
first above written.

[SEAL]                                WILLIAMS HOLDINGS OF DELAWARE, INC.

Attest

/s/ SHAWNA L. GEHRES                  By: /s/ JAMES G. IVEY
---------------------------              ---------------------------------
Name:  Shawna L. Gehres               Name:  James G. Ivey
Title: Secretary                      Title: Treasurer

[SEAL]                                THE WILLIAMS COMPANIES, INC.

Attest

/s/ SHAWNA L. GEHRES                  By: /s/ JAMES G. IVEY
---------------------------              ---------------------------------
Name:  Shawna L. Gehres               Name:  James G. Ivey
Title: Secretary                      Title: Treasurer

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[SEAL]                                THE FIRST NATIONAL BANK OF CHICAGO,
                                      AS TRUSTEE
Attest

/s/ SOMSRI HELMER                     By: /s/ R. J. BRUNER
---------------------------              ---------------------------------
Name:  Somsri Helmer                  Name:  R. J. Bruner
Title: Trust Officer                  Title: Vice President

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