Exhibit 99.1

 FORM OF CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002
                                (WILLIAM J. POST)

     I, William J. Post, the Chairman of the Board and Chief Executive Officer
of Pinnacle West Capital Corporation ("Pinnacle West"), certify, to the best of
my knowledge, that: (a) the attached Quarterly Report on Form 10-Q of Pinnacle
West for the fiscal quarter ended March 31, 2003 (the "March 2003 Form 10-Q")
fully complies with the requirements of Section 13(a) or 15(d) of the Securities
Exchange Act of 1934 and (b) the information contained in the March 2003 Form
10-Q Report fairly presents, in all material respects, the financial condition
and results of operations of Pinnacle West.


                                        William J. Post
                                        ----------------------------------------
                                        William J. Post
                                        Chairman of the Board and
                                        Chief Executive Officer

                                        Date: May 14, 2003