<PAGE>   1

                                                                    Exhibit 4.11







================================================================================






                                   ONEOK, INC.

                                   7.75% NOTES

                                    Due 2005


                                 ---------------


                          SIXTH SUPPLEMENTAL INDENTURE

                            Dated as of March 1, 2000


                                 ---------------


                    Chase Bank of Texas, National Association
                                     TRUSTEE




================================================================================

<PAGE>   2
       THIS SIXTH SUPPLEMENTAL INDENTURE is made as of the 1st day of March,
2000, by and between ONEOK, INC., an Oklahoma corporation (the "Company"), and
CHASE BANK OF TEXAS, NATIONAL ASSOCIATION, a national banking association (the
"Trustee").

                              W I T N E S S E T H:

       WHEREAS, the Company has heretofore entered into an Indenture, dated as
of September 24, 1998 (the "Original Indenture"), with the Trustee;

       WHEREAS, the Original Indenture is incorporated herein by this reference
and the Original Indenture, as supplemented by this Sixth Supplemental
Indenture, is herein called the "Indenture";

       WHEREAS, under the Original Indenture, a new series of Securities may at
any time be established pursuant to a supplemental indenture executed by the
Company and the Trustee;

       WHEREAS, the Company proposes to create under the Indenture a new series
of Securities; and

       WHEREAS, all conditions necessary to authorize the execution and delivery
of this Sixth Supplemental Indenture and to make it a valid and binding
obligation of the Company have been done or performed.

       NOW, THEREFORE, in consideration of the agreements and obligations set
forth herein and for other good and valuable consideration, the sufficiency of
which is hereby acknowledged, the parties hereto hereby agree as follows:

                                    ARTICLE 1

                              7.75% NOTES DUE 2005

       SECTION 101. Establishment. There is hereby established a new series of
Securities to be issued under the Indenture, to be designated as the Company's
7.75% Notes Due 2005 (the "Notes").

       There are to be authenticated and delivered $350,000,000 principal amount
of Notes to be issued and delivered to the initial purchasers thereof at 99.837%
of principal amount. The Company shall have the right to issue additional Notes
at any time upon compliance with the applicable provisions of the Indenture. The
Notes shall be issued in definitive fully registered form.

       The Notes shall be issued in the form of one or more Global Securities,
each in substantially the form set out in Exhibit A hereto, except for changes
to be reflected in the Exchange Notes (as hereinafter defined) by reason of
their registration under the Securities Act of 1933, to eliminate provisions
relating to liquidated damages, registration rights and transfer restrictions
and to reflect interest accrual provisions. The initial Depositary with respect
to the Notes shall be The Depository Trust Company.



<PAGE>   3

       The Company will not pay Additional Amounts, as defined in Section 1008
of the Original Indenture.

       The form of the Trustee's Certificate of Authentication for the Notes
shall be in substantially the form set forth in Exhibit B hereto.

       Each Note shall be dated the date of authentication thereof. Each Note
shall bear interest from the Original Issue Date, except for Exchange Notes,
which shall bear interest from the last interest payment date on which interest
was paid on the Note surrendered in exchange therefor or, if no interest has
been paid on that Note, from the Original Issue Date.

       The interest rate on the Notes will not be reset pursuant to Section
308(b) of the Original Indenture and the Stated Maturity shall not be extended
pursuant to Section 309 of the Original Indenture.

       SECTION 102. Definitions. The following defined terms used herein shall,
unless the context otherwise requires, have the meanings specified below.
Capitalized terms used herein for which no definition is provided herein shall
have the meanings set forth in the Original Indenture.

       "Adjusted Treasury Rate" means, with respect to any Redemption Date, the
rate per annum equal to the semiannual equivalent yield to maturity of the
Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue
(expressed as a percentage of its principal amount) equal to the Comparable
Treasury Price for such Redemption Date, plus .20%.

       "Comparable Treasury Issue" means the United States Treasury security
selected by a Quotation Agent as having a maturity comparable to the remaining
term of the Notes to be redeemed that would be utilized, at the time of
selection and in accordance with customary financial practice, in pricing new
issues of corporate debt securities of comparable maturity to the remaining term
of the Notes.

       "Comparable Treasury Price" means, with respect to any Redemption Date,
(i) the average of the Reference Treasury Dealer Quotations for such Redemption
Date, after excluding the highest and lowest such Reference Treasury Dealer
Quotations, or (ii) if the Company obtains fewer than three such Reference
Treasury Dealer Quotations, the average of all such Reference Treasury Dealer
Quotations.

         "Exchange Notes" means securities that will have terms identical in all
material respects to the Notes (except with respect to liquidated damages,
registration rights, transfer restrictions and interest accrual provisions),
which will be offered in exchange for Notes tendered in exchange therefor at the
option of the holders thereof, pursuant to an exchange offer for the
then-outstanding Notes in accordance with the terms of the Registration Rights
Agreement.

       "Interest Payment Dates" means March 1 and September 1 of each year.

       "Original Issue Date" means March 1, 2000.



                                       2
<PAGE>   4

       "Quotation Agent" means one of the Reference Treasury Dealers appointed
by the Company and certified to the Trustee by the Company.

       "Reference Treasury Dealer" means (i) each of Banc of America Securities
LLC, Banc One Capital Markets, Inc., First Union Securities, Inc., J.P. Morgan
Securities Inc., PaineWebber Incorporated and Salomon Smith Barney Inc.
(collectively, the "Initial Purchasers") and their respective successors;
provided, however, that if any of the foregoing shall cease to be a primary U.S.
Government Securities dealer in New York City (a "Primary Treasury Dealer"), the
Company shall substitute therefor another Primary Treasury Dealer and certify
the same to the Trustee; and (ii) any other Primary Treasury Dealer selected by
the Company and certified to the Trustee.

       "Reference Treasury Dealer Quotations" means, with respect to each
Reference Treasury Dealer and any Redemption Date, the average, as determined by
the Company and certified to the Trustee by the Company, of the bid and asked
prices for the Comparable Treasury Issue (expressed in each case as a percentage
of its principal amount) quoted in writing to the Company by such Reference
Treasury Dealer at 5:00 p.m., New York City time, on the third Business Day
preceding such Redemption Date.

       "Registration Rights Agreement" means the agreement dated as of the date
hereof, by and among the Company and the Initial Purchasers, which provides to
the holders of Notes certain registration rights as set forth therein.

       "Regular Record Date" means February 15 in the case of a March 1 Interest
Payment Date and August 15 in the case of a September 1 Interest Payment Date.

       "Stated Maturity" means March 1, 2005.

       SECTION 103. Payment of Principal and Interest. The principal of the
Notes shall be due at Stated Maturity (unless earlier redeemed). The unpaid
principal amount of the Notes shall bear interest at the rate of 7.75% per annum
until paid or duly provided for. Interest shall be paid semi-annually in arrears
on each Interest Payment Date to the Person in whose name the Notes are
registered on the Regular Record Date for such Interest Payment Date and on
Stated Maturity. Accrued interest paid on Stated Maturity shall be paid to the
Person to whom principal is paid. Any such interest that is not so punctually
paid or duly provided for will forthwith cease to be payable to the Holders on
such Regular Record Date and may be paid to the Person or Persons in whose name
the Notes are registered at the close of business on a Special Record Date for
the payment of such defaulted interest to be fixed by the Trustee, notice
whereof shall be given to Holders of the Notes not less than ten days prior to
such Special Record Date.

       Payments of interest on the Notes will include interest accrued to but
excluding the respective Interest Payment Dates. Interest payments for the Notes
shall be computed and paid on the basis of a 360-day year of twelve 30-day
months.

       Payment of the principal and interest due at the Stated Maturity or
earlier redemption of the Notes shall be made upon surrender of the Notes at the
office or agency of the Company in the Borough of Manhattan, City and State of
New York or at the Corporate Trust Office of the Trustee. The principal of and
interest on the Notes shall be paid in such currency of the United


                                       3
<PAGE>   5

States of America as at the time of payment is legal tender for payment of
public and private debts. Payments of interest will be made at the option of the
Company, (i) by check mailed to the address of the Person entitled thereto as
such address shall appear in the Security Register or (ii) by wire transfer to
an account located in the United States maintained by the payee.

       SECTION 104. Denominations. The Notes may be issued in denominations of
$1,000 and any integral multiple thereof.

       SECTION 105. Global Securities. The Notes will be issued in the form of
one or more Global Securities registered in the name of the Depositary or its
nominee. Except under the limited circumstances described below, Notes
represented by the Global Security will not be exchangeable for, and will not
otherwise be issuable as, Notes in definitive form. The Global Securities
described above may not be transferred except by the Depositary to a nominee of
the Depositary or by a nominee of the Depositary to the Depositary or another
nominee of the Depositary or to a successor Depositary or its nominee.

       Owners of beneficial interests in such a Global Security will not be
considered the Holders thereof for any purpose under the Indenture, and no
Global Security representing a Note shall be exchangeable, except for another
Global Security of like denomination and tenor to be registered in the name of
the Depositary or its nominee or to a successor Depositary or its nominee. The
rights of Holders of such Global Security shall be exercised only through the
Depositary.

       A Global Security shall be exchangeable for Notes registered in the names
of persons other than the Depositary or its nominee only if (i) the Depositary
notifies the Company that it is unwilling or unable to continue as a Depositary
for such Global Security and no successor Depositary shall have been appointed
by the Company, or if at any time the Depositary ceases to be a clearing agency
registered under the Securities Exchange Act of 1934, as amended, at a time when
the Depositary is required to be so registered to act as such Depositary and no
successor Depositary shall have been appointed by the Company, in each case
within 90 days after the Company receives such notice or becomes aware of such
cessation, (ii) the Company in its sole discretion determines that such Global
Security shall be so exchangeable, or (iii) there shall have occurred an Event
of Default with respect to the Notes.

       SECTION 106. Transfer. No service charge will be made for any transfer or
exchange of Notes, but payment will be required of a sum sufficient to cover any
tax or other governmental charge that may be imposed in connection therewith.

       SECTION 107. Redemption at the Company's Option. The Notes will be
redeemable, in whole or in part, at any time at the option of the Company at a
redemption price (the "Redemption Price") equal to the greater of (i) 100% of
the principal amount of the Notes to be redeemed or (ii) as determined by a
Quotation Agent, the sum of the present values of the remaining scheduled
payments of principal and interest on the Notes to be redeemed that are payable
after the date of redemption (the "Redemption Date") discounted to the
Redemption Date on a semiannual basis (assuming a 360-day year consisting of
twelve 30-day months) at the Adjusted Treasury Rate, plus, in each case, accrued
but unpaid interest to the Redemption Date.


                                       4
<PAGE>   6

       Notice of any redemption will be mailed at least 30 days but not more
than 60 days before the Redemption Date to each Holder of the Notes to be
redeemed. Unless the Company defaults in payment of the Redemption Price,
interest will cease to accrue on the Notes or portions thereof called for
redemption on and after the Redemption Date.

       SECTION 108. Other Terms.

       The Notes will not have a sinking fund.

       Notice of redemption shall be given as provided in Section 1104 of the
Original Indenture.

       Any redemption of less than all of the Notes shall, with respect to the
principal thereof, be divisible by $1,000.

                                    ARTICLE 2

                            MISCELLANEOUS PROVISIONS

       SECTION 201. Recitals by Company. The recitals in this Sixth Supplemental
Indenture are made by the Company only and not by the Trustee, and all of the
provisions contained in the Original Indenture in respect of the rights,
privileges, immunities, powers and duties of the Trustee shall be applicable in
respect of Notes and of this Sixth Supplemental Indenture as fully and with like
effect as if set forth herein in full.

       SECTION 202. Ratification and Incorporation of Original Indenture. The
Original Indenture is in all respects ratified and confirmed, and the Original
Indenture and this Sixth Supplemental Indenture shall be read, taken and
construed as one and the same instrument; provided that, in the case of a
conflict between this Sixth Supplemental Indenture and the Original Indenture,
this Sixth Supplemental Indenture shall control.

       SECTION 203. Executed in Counterparts. This Sixth Supplemental Indenture
may be simultaneously executed in several counterparts, each of which shall be
deemed to be an original, and such counterparts shall together constitute one
and the same instrument.

       SECTION 204. Parties Interested Herein. Nothing in the Indenture
expressed or implied is intended or shall be construed to confer upon, or to
give or grant to, any person or entity, other than the Company, the Trustee, the
Paying Agent and the registered owners of the Notes, any right, remedy or claim
under or by reason of the Indenture or any covenant, condition or stipulation
hereof, and all covenants, stipulations, promises and agreements in the
Indenture contained by and on behalf of the Company shall be for the sole and
exclusive benefit of the Company, the Trustee, the Paying Agent and the
registered owners of the Notes.


                                       5
<PAGE>   7

            IN WITNESS WHEREOF, each party hereto has caused this Sixth
Supplemental Indenture to be signed in its name and behalf by its duly
authorized officers or signatories, all as of the day and year first above
written.

ATTEST:                                            ONEOK, INC.



By: /s/ Deborah R. Barnes                          By: /s/ Jim Kneale
   ----------------------------------------           -------------------------



ATTEST:                                            CHASE BANK OF TEXAS, NATIONAL
                                                    ASSOCIATION, as Trustee


By:  /s/ Mauri J. Cowen                            By: /s/ John G. Jones
   -----------------------------------------           ------------------------
   Authorized Signatory                                Authorized Signatory



                                       6
<PAGE>   8

                                                                      EXHIBIT A


                                  FORM OF NOTE


                                   [Attached]

NOTE: FOLLOWING REGISTRATION OF THE NOTES UNDER THE SECURITIES ACT OF 1933,
APPROPRIATE CHANGES WILL BE MADE IN THE FORM OF NOTE AS CONTEMPLATED BY THE
INDENTURE.




<PAGE>   9

       THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE
INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITORY
OR A NOMINEE THEREOF. THIS SECURITY MAY NOT BE EXCHANGED IN WHOLE OR IN PART FOR
A SECURITY REGISTERED, AND NO TRANSFER OF THIS SECURITY IN WHOLE OR IN PART MAY
BE REGISTERED, IN THE NAME OF ANY PERSON OTHER THAN SUCH DEPOSITORY OR ITS
NOMINEE EXCEPT IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE.

       UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF
THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE ISSUER OR
ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE, OR PAYMENT, AND ANY
CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME
AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE
TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE, OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

================================================================================

No. __


                                   ONEOK, INC.
                              7.75% NOTES DUE 2005

                                CUSIP: 682680AG8

       ONEOK, Inc., an Oklahoma corporation (herein called "Company," which
term includes any successor corporation under the Indenture referred to herein),
for value received, hereby promises to pay to:

       CEDE & CO.

or registered assigns, the principal sum of

       *__________________ DOLLARS*

on March 1, 2005 and to pay interest on such principal sum at the rate of seven
and three-fourths percent (7.75%) per annum.


================================================================================

       THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 (THE
"SECURITIES ACT"), AND THIS NOTE MAY NOT BE OFFERED, SOLD,
<PAGE>   10

PLEDGED OR OTHERWISE TRANSFERRED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION
STATEMENT OR IN ACCORDANCE WITH AN APPLICABLE EXEMPTION FROM THE REGISTRATION
REQUIREMENTS OF THE SECURITIES ACT (SUBJECT TO THE DELIVERY OF SUCH EVIDENCE, IF
ANY, REQUIRED UNDER THE INDENTURE PURSUANT TO WHICH THIS NOTE IS ISSUED) AND IN
ACCORDANCE WITH ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES
OR ANY OTHER JURISDICTION. EACH PURCHASER OF THE SECURITY EVIDENCED HEREBY IS
HEREBY NOTIFIED THAT THE SELLER MAY BE RELYING ON THE EXEMPTION FROM THE
PROVISIONS OF SECTION 5 OF THE SECURITIES ACT PROVIDED BY RULE 144A THEREUNDER
OR ANOTHER EXEMPTION UNDER THE SECURITIES ACT. THE HOLDER OF THE SECURITY
EVIDENCED HEREBY AGREES FOR THE BENEFIT OF THE COMPANY THAT (A) SUCH SECURITY
MAY BE RESOLD, PLEDGED OR OTHERWISE TRANSFERRED ONLY (1)(A) TO A PERSON WHO THE
SELLER REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL BUYER (AS DEFINED IN
RULE 144A UNDER THE SECURITIES ACT) IN A TRANSACTION MEETING THE REQUIREMENTS OF
RULE 144A, (B) IN A TRANSACTION MEETING THE REQUIREMENTS OF RULE 144 UNDER THE
SECURITIES ACT, (C) OUTSIDE THE UNITED STATES TO A FOREIGN PERSON IN A
TRANSACTION MEETING THE REQUIREMENTS OF RULE 904 UNDER THE SECURITIES ACT OR (D)
IN ACCORDANCE WITH ANOTHER EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE
SECURITIES ACT (AND BASED UPON AN OPINION OF COUNSEL IF THE COMPANY SO
REQUESTS), AS LONG AS THE REGISTRAR RECEIVES A CERTIFICATION OF THE TRANSFEROR
AND AN OPINION OF COUNSEL THAT SUCH TRANSFER IS IN COMPLIANCE WITH THE
SECURITIES ACT, (2) TO THE COMPANY OR (3) PURSUANT TO AN EFFECTIVE REGISTRATION
STATEMENT AND, IN EACH CASE, IN ACCORDANCE WITH ANY APPLICABLE SECURITIES LAWS
OF ANY STATE OF THE UNITED STATES OR ANY OTHER APPLICABLE JURISDICTION AND (B)
THE HOLDER WILL AND EACH SUBSEQUENT HOLDER IS REQUIRED TO NOTIFY ANY PURCHASER
FROM IT OF THE SECURITY EVIDENCED HEREBY OF THE RESALE RESTRICTION SET FORTH IN
(A) ABOVE.

       The Company will pay interest from March 1, 2000, semi-annually on March
1 and September 1 of each year, and on the date of maturity, commencing
September 1, 2000 (each such date an "Interest Payment Date"), until the
principal hereof is otherwise paid or duly provided for. The interest so
payable, and punctually paid or duly provided for, on any Interest Payment Date
will, as provided in the Indenture (as defined below), be paid to the holder of
this Note (the "Holder") of record at the close of business on the regular
record date (the "Regular Record Date") for such Interest Payment Date, which
shall be February 15 (in the case of the March 1 Interest Payment Date) or
August 15 (in the case of the September 1 Interest Payment Date), whether or not
a Business Day. Interest will be computed on the basis of a 360-day year of
twelve 30-day months.

       Any such interest not so punctually paid or duly provided for shall
forthwith cease to be payable to the Holder on such Regular Record Date by
virtue of his having been such Holder, and may be paid to the Holder of record
of this Note at the close of business on a special record date (the "Special
Record Date") fixed by the Company for the payment of such defaulted interest,
notice whereof shall be given to Holders not less than 10 days prior to such
Special Record Date, all as more fully provided in the Indenture.

<PAGE>   11

       Payment of the principal of this Note and the interest thereof will be
made at the office or agency of the Company in the Borough of Manhattan, City
and State of New York or at the Corporate Trust Office of the Trustee in such
currency of the United States of America as at the time of payment is legal
tender for payment of public and private debts.




<PAGE>   12

                                   ONEOK, INC.
                              7.75% Notes Due 2005

       This Note is one of a duly authorized issue of debt securities of the
Company (herein called the "Securities"), issuable in one or more series, issued
and to be issued under and pursuant to an Indenture dated as of September 24,
1998, as amended and supplemented by that certain Sixth Supplemental Indenture
(the "Indenture"), duly executed and delivered by the Company to Chase Bank of
Texas, National Association, as trustee (the "Trustee," which term includes any
successor trustee under the Indenture) and is one of a series unlimited in
aggregate principal amount and designated as 7.75% Notes Due 2005 (the "Notes").
Reference is hereby made to the Indenture for a description of the rights,
limitations of rights, obligations, duties and immunities thereunder of the
Trustee, the Company and the holders of Securities (including Holders of the
Notes).

       If (i)(a) the Company has not filed a registration statement
(the "Exchange Offer Registration Statement") under the Securities Act
registering a security substantially identical to this Note (except that such
note (the "Exchange Note") will not contain terms with respect to liquidated
damages or transfer restrictions) pursuant to an exchange offer (the "Exchange
Offer") within 120 days after this Note is issued (the "Issue Date"), (b) the
Exchange Offer Registration Statement has not become or been declared effective
within 210 days after the Issue Date or (c) the Exchange Offer has not been
consummated within 35 days after the Exchange Offer Registration Statement is
declared effective (unless changes in law or the applicable interpretations of
the staff of the Division of Corporate Finance of the Securities and Exchange
Commission do not permit the Company to effect the Exchange Offer) or (ii) a
registration statement registering this Note for resale (a "Shelf Registration
Statement") has not been declared effective (or shall thereafter cease to be
effective, subject to certain exceptions, prior to the earlier of the second
anniversary of the Issue Date and the date on which all transfer restricted
notes have been sold thereunder) on or prior to the later of the 245th calendar
day after the Issue Date and the 60th calendar day after the publication of the
change in law or interpretation, then the interest rate borne by this Note will
be increased by one-half of one percent per annum for the first 90 days
following the deadline for the Exchange Offer Registration Statement to be filed
or declared effective or for the Exchange Offer to be consummated, as
applicable, in the case of clause (i) above, or following such 245th or 60th
calendar day, as applicable, in the case of clause (ii) above, and will be
increased by an additional one-half of one percent per annum after the end of
such period, except under the circumstances described in the succeeding
sentence, as liquidated damages. Upon (x) filing of the Exchange Offer
Registration Statement after the deadline for it to be filed, declaration of the
effectiveness of the Exchange Offer Registration Statement after the deadline
for it to be declared effective or consummation of the Exchange Offer after the
deadline for its consummation, as applicable, as described in clause (i) above,
or (y) the effectiveness of the Shelf Registration Statement after the 245th or
60th calendar day, as applicable, described in clause (ii) above (or if the
Shelf Registration Statement ceased to be effective as described above, after
the Shelf Registration Statement again becomes effective subject to certain
specified exceptions), any such increase in the interest rate will cease to be
effective. The aggregate amount of liquidated damages pursuant to such
provisions will not exceed one percent per annum.

       The Notes are subject to defeasance at the option of the Company as
provided in the Indenture.

<PAGE>   13

       As long as this Note is represented in global form (the "Global
Security") registered in the name of the Depository or its nominee, except as
provided in the Indenture and subject to certain limitations therein set forth,
no Global Security shall be exchangeable or transferable.

       If an Event of Default (as defined in the Indenture) with respect to
the Notes shall occur and be continuing, the principal plus any accrued interest
may be declared due and payable in the manner and with the effect and subject to
the conditions provided in the Indenture.

       The Indenture permits the amendment thereof and the modification of the
rights and obligations of the Company and the rights of the Holders under the
Indenture at any time by the Company and the Trustee with the consent of the
Holders of a majority in aggregate principal amount of the Securities then
Outstanding (as defined in the Indenture) of all series that are affected by
such amendment or modification, except that certain amendments that do not
adversely affect the rights of any holder of the Securities may be made without
the approval of holders of the Securities. No amendment or modification may,
among other things, change the Stated Maturity of any Security, reduce the
principal amount thereof, reduce the rate or change the time of payment of any
interest thereon, or reduce the aforesaid majority in aggregate principal amount
of Securities of any series, consent of the holders of which is required for any
such amendment or modification, without the consent of each Securityholder
affected.

       Notwithstanding any provision in the Indenture or any provision of this
Note, the Holder of this Note shall have the right, which is absolute and
unconditional, to receive payment of the principal of (and premium, if any) and
interest on this Note at the times, places and rate, and in the currency herein
prescribed.

       The Notes may be redeemed, in whole or in part, at any time at the
option of the Company at a Redemption Price equal to the greater of (i) 100% of
the principal amount of the Notes to be redeemed or (ii) as determined by a
Quotation Agent, the sum of the present values of the remaining scheduled
payments of principal and interest on the Notes to be redeemed that are payable
after the Redemption Date discounted to the Redemption Date on a semiannual
basis (assuming a 360-day consisting of twelve 30-day months) at the Adjusted
Treasury Rate, plus, in each case, accrued but unpaid interest to the Redemption
Date.

       In the event of redemption of this Note in part only, a new Note or
Notes of this series for the unredeemed portion hereof will be issued in the
name of the Holder upon surrender hereof or otherwise reduced in accordance with
the provisions of the Indenture. The Notes will not have a sinking fund.

       THIS NOTE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE
LAWS OF THE STATE OF NEW YORK, WITHOUT REGARD TO PRINCIPLES OF CONFLICTS OF
LAWS.

       All terms used in this Note but not defined herein have the meanings
assigned to them in the Indenture.

       Unless the certificate of authentication hereon has been executed by or
on behalf of the Trustee by manual signature, this Note shall not be entitled to
any benefit under the Indenture or be valid or obligatory for any purpose.

<PAGE>   14

       IN WITNESS WHEREOF, the Company has caused this Note to be duly
executed.

                                     ONEOK, INC.


                                     By:
                                           ------------------------------------
                                     Name:
                                           ------------------------------------
                                     Title:
                                           ------------------------------------



                                     Attested:
                                              ---------------------------------
                                     Name:
                                              ---------------------------------
                                     Title:
                                              ---------------------------------


TRUSTEE'S CERTIFICATE OF AUTHENTICATION

Dated:
      -------------
This is one of the Notes referred to in the within-
mentioned Indenture.


                              CHASE BANK OF TEXAS, NATIONAL ASSOCIATION
                                as Trustee


                              By:
                                 --------------------------------------
                                 Authorized Signatory

<PAGE>   15

                  SCHEDULE OF EXCHANGES OF INTEREST IN THE NOTE

       The following exchanges of interests in this Note have been made:

<TABLE>
<CAPTION>
                                                                            Principal Amount of
                          Amount of decrease     Amount of increase         this Note following        Signature of authorized
     Date of Exchange        in this Note           in this Note        such decrease or (increase)     signatory of Trustee
<S>                       <C>                    <C>                    <C>

</TABLE>

<PAGE>   16



                             CERTIFICATE OF TRANSFER

To assign this Note, fill in the form below:

I or we assign and transfer this Note to

       (Print or type assignee's name, address and zip code)

       (Insert assignee's soc. sec. or tax I.D. No.)


and irrevocably appoint __________________ agent to transfer this Note on the
books of ONEOK, Inc.  The agent may substitute another to act for him.



----------------------------------------------------------------

Date:                    Your Signature:
     ------------------                 ------------------------

----------------------------------------------------------------
Sign exactly as your name appears on the other side of this Note.



       THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME AS IT
APPEARS ON THE FIRST PAGE OF THE NOTE.

       THE SIGNATURE MUST BE GUARANTEED BY AN "ELIGIBLE GUARANTOR INSTITUTION"
THAT IS A MEMBER OR PARTICIPANT IN A "SIGNATURE GUARANTEE PROGRAM" (E.G., THE
SECURITIES TRANSFER AGENTS MEDALLION PROGRAM, THE STOCK EXCHANGE MEDALLION
PROGRAM OR THE NEW YORK STOCK EXCHANGE, INC. MEDALLION PROGRAM).


<PAGE>   17

In connection with any transfer of any of the Notes evidenced by this
certificate occurring prior to the expiration of the period referred to in Rule
144(k) under the Securities Act of 1933 (the "Securities Act") after the later
of the date of original issuance of such Notes and the last date, if any, on
which such Notes were owned by ONEOK, Inc. or any Affiliate, the undersigned
confirms that such Notes are being transferred in accordance with the terms of
such Notes:

CHECK ONE BOX BELOW

    (1)   [ ]  to ONEOK, Inc.; or

    (2)   [ ]  pursuant to an effective registration statement under the
               Securities Act; or

    (3)   [ ]  inside the United States to a "qualified institutional buyer"
               (as defined in Rule 144A under the Securities Act) that purchases
               for its own account or for the account of a qualified
               institutional buyer to whom notice is given that such transfer is
               being made in reliance on Rule 144A under the Securities Act, in
               each case pursuant to and in compliance with Rule 144A under the
               Securities Act; or

    (4)   [ ]  outside the United States in an offshore transaction within the
               meaning of Regulation S under the Securities Act in compliance
               with Rule 904 under the Securities Act; or

    (5)   [ ]  pursuant to another available exemption from registration
               provided by Rule 144 under the Securities Act.

     Unless one of the boxes is checked, the Trustee will refuse to register any
     of the Notes evidenced by this certificate in the name of any person other
     than the registered holder thereof; provided, however, that if box (3), (4)
     or (5) is checked, the Trustee may require, prior to registering any such
     transfer of the Notes, such legal opinions, certifications and other
     information as the Company has reasonably requested to confirm that such
     transfer is being made pursuant to an exemption from, or in a transaction
     not subject to, the registration requirements of the Securities Act, such
     as the exemption provided by Rule 144 under the Securities Act.

<PAGE>   18


------------------------------
Signature



Signature Guarantee:


-------------------------------             -------------------------------
[Signature must be guaranteed               Signature
by an eligible Guarantor
Institution (banks, stock
brokers, savings and loan
associations and credit
unions) with membership in
an approved guarantee
medallion program pursuant
to Securities and Exchange
Commission Rule 17Ad-15]





              TO BE COMPLETED BY PURCHASER IF (3) ABOVE IS CHECKED.

                The undersigned represents and warrants that it is purchasing
this Note for its own account or an account with respect to which it exercises
sole investment discretion and that it and any such account is a "qualified
institutional buyer" within the meaning of Rule 144A under the Securities Act,
and is aware that the sale to it is being made in reliance on Rule 144A under
the Securities Act and acknowledges that it has received such information
regarding the Company as the undersigned has requested pursuant to Rule 144A
under the Securities Act or has determined not to request such information and
that it is aware that the transferor is relying upon the foregoing
representations of the undersigned in order to claim the exemption from
registration provided by Rule 144A under the Securities Act.


Dated:
       ----------------          ----------------------------------------------
                                 NOTICE: To be executed by an executive officer

<PAGE>   19

                                                                      EXHIBIT B


                          CERTIFICATE OF AUTHENTICATION

       This is one of the Notes referred to in the within-mentioned Indenture.

                                       CHASE BANK OF TEXAS, NATIONAL
                                        ASSOCIATION, as Trustee [or Successor
                                        Trustee]



     Dated:                            By:
           -------------------------      -----------------------------------
                                          Authorized Signatory