
<PAGE>   1
                                                                    EXHIBIT 99.a


ONEOK FINANCIAL NEWS



ONEOK, INC.                                 CONTACT: WELDON WATSON, 918/588-7158
P. O. BOX 871
TULSA, OK 74102-0871                       FOR IMMEDIATE RELEASE, AUGUST 6, 1999






                     SOUTHERN UNION LOSES TWO COURT BATTLES

         TULSA, Oklahoma - Southern Union (NYSE:SUG) failed in two separate
court actions to delay a shareholder vote and the regulatory approval process
for the pending merger of ONEOK, Inc. (NYSE:OKE), and Southwest Gas Corporation
(NYSE:SWX).

         Southern Union made an attempt on Thursday, August 5, in a California
state court to obtain a restraining order to halt the Southwest shareholder
meeting scheduled for next Tuesday, August 10, 1999. The California judge denied
that motion. Later in the day, Southern Union attempted to obtain another
restraining order from a federal court in Phoenix to halt the regulatory
approval process for the merger. That attempt also failed.

         The basis for the latest court actions by Southern Union was a
complaint filed in the Phoenix federal court on July 19, in which it alleges
ONEOK and others attempted to illegally prevent Southern Union's hostile bid for
Southwest Gas Corporation.

         ONEOK has filed a contempt motion against Southern Union for violating
a federal preliminary injunction, issued by U. S. District Judge Sven Eric
Holmes of the Northern District of Oklahoma, which prevented Southern Union from
influencing a shareholder vote on the merger.

         In denying the restraining order in the Phoenix federal court, U. S.
District Judge Roslyn Silver said she found nothing that suggests a crime in the
filings presented to her by Southern Union.

         Larry Brummett, chairman and chief executive officer of ONEOK, said,
"Obviously, Southern Union is having a very difficult time getting a court in
any jurisdiction to pay any attention to its unfounded accusations. We are
confident we can finalize this merger in a timely manner in the best interests
of shareholders, customers and employees."

         ONEOK, Inc., is an integrated natural gas company involved in
production, processing, gathering, storage and transmission. The company is also
the largest natural gas distributor in Kansas and Oklahoma, operating as Kansas
Gas Service Company and Oklahoma Natural Gas Company, serving 1.4 million
customers.

                                     # # #

STATEMENTS CONTAINED IN THIS RELEASE THAT INCLUDE COMPANY EXPECTATIONS OR
PREDICTIONS AS TO THE ACCRETIVE NATURE OF THE TRANSACTION AND ITS EXPECTED
CONSUMMATION ARE FORWARD-LOOKING STATEMENTS INTENDED TO BE COVERED BY THE SAFE
HARBOR PROVISIONS OF THE SECURITIES ACT OF 1933 AND THE SECURITIES EXCHANGE ACT
OF 1934. IT IS IMPORTANT TO NOTE THAT THE ACTUAL RESULTS COULD DIFFER MATERIALLY
FROM THOSE PROJECTED IN SUCH FORWARD-LOOKING STATEMENTS. AMONG THE IMPORTANT
FACTORS THAT COULD AFFECT ACTUAL RESULTS ARE THE TIMING AND TERMS OF REGULATORY
APPROVALS AND OPERATING RESULTS OF ONEOK AND SOUTHWEST GAS. MORE INFORMATION
ABOUT THE ONEOK AND SOUTHWEST GAS TRANSACTION CAN BE FOUND UNDER COMPANY NEWS ON
THE ONEOK WEB SITE AT www.oneok.com. SERVICE AREA MAPS AND LOGOS ARE AVAILABLE
UNDER MEDIA KIT.


