
<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549



                                    FORM 8-K


                                 CURRENT REPORT
                     PURSUANT TO SECTION 13 OR 15(d) OF THE
                        SECURITIES EXCHANGE ACT OF 1934



                                October 14, 1999
                Date of Report (Date of earliest event reported)



                                  ONEOK, Inc.
             (Exact name of registrant as specified in its charter)



         Oklahoma                        1-2572                 73-1520922
(State or other jurisdiction          (Commission             (IRS Employer
       of incorporation)              File Number)          Identification No.)


                        100 West Fifth Street; Tulsa, OK
                    (Address of principal executive offices)


                                     74103
                                   (Zip code)


                                 (918) 588-7000
              (Registrant's telephone number, including area code)


                                 Not Applicable
         (Former name or former address, if changed since last report)



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Items 1 - 4.      Not Applicable.

Item 5.           Other Events.

                  ONEOK, Inc., Chairman and CEO Larry Brummett addressed the
Oklahoma Corporation Commission to say the false allegations about a 1993 gas
purchase contract may jeopardize the planned merger between ONEOK and Southwest
Gas.
                  On October 13, 1999, the Company issued a press release, a
copy of which is attached hereto as exhibit 99.a and incorporated herein by
reference.

Item 6.           Not Applicable

Item 7.           Financial Statements, Pro Forma Financial Information and
                  Exhibits.

<TABLE>
<CAPTION>
Exhibit
No.               Description
-------           -----------
<S>               <C>
99.a              Press release issued by ONEOK, Inc. dated October 13, 1999.

Items 8-9.        Not Applicable
</TABLE>









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                                   SIGNATURE

         Pursuant to the requirements of the Securities Exchange Act of 1934,
the registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized, on this 14th day of October 1999.


                                         ONEOK, Inc.

                                         By: /s/ Jim Kneale
                                             --------------------------------
                                             Jim Kneale
                                             Vice President, Chief Financial
                                             Officer, and Treasurer





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                               INDEX TO EXHIBITS


<TABLE>
<CAPTION>
Exhibit
No.               Description
-------           -----------
<S>               <C>
99.a              Press release issued by ONEOK, Inc. dated October 13, 1999.

</TABLE>

