Exhibit 5.1

                                   May 7, 2003

Arizona Public Service Company
400 North 5th Street
Phoenix, Arizona  85004

Ladies and Gentlemen:

     Reference is made to (a) your proposed  offering of up to  $500,000,000  of
your   securities,   as   contemplated  by  the   registration   statement  (the
"Registration  Statement")  on Form  S-3,  No.  333-90824  filed by you with the
Securities and Exchange  Commission (the "Commission")  under the Securities Act
of 1933, as amended (the "Act"),  on June 20, 2002, as amended by  Pre-Effective
Amendment  No. 1 thereto,  filed with the  Commission  on August 27,  2002,  and
Pre-Effective  Amendment No. 2 thereto,  filed with the  Commission on September
19, 2002,  and declared  effective by the  Commission on October 9, 2002,  which
securities  include first mortgage bonds,  debt  securities,  or any combination
thereof;  and (b) your  issuance and sale of  $300,000,000  aggregate  principal
amount of 4.650%  Notes due May 1,  2015 and  $200,000,000  aggregate  principal
amount of 5.625% Notes due May 1, 2033  (collectively the "Notes"),  pursuant to
the  Underwriting  Agreement  dated May 7, 2003 (the  "Underwriting  Agreement")
between you and the  underwriters  named therein and the  Indenture  dated as of
January 15, 1998, as amended and  supplemented to the date hereof and as further
amended and supplemented by the Seventh Supplemental  Indenture thereto dated as
of May 1, 2003,  in  substantially  the form filed by you as Exhibit 4.1 to your
Form 8-K Report dated May 7, 2003 (the "Indenture").

     We have examined the definitive  prospectus,  dated September 19, 2002, and
the  prospectus  supplement,  dated May 7, 2003 (the  prospectus  and prospectus
supplement, and all material incorporated therein by reference being hereinafter
referred to as the  "Prospectus"),  relating to the Notes. We have also examined
originals or copies,  certified or otherwise identified to our satisfaction,  of
such corporate records, agreements, and other instruments, certificates, orders,
opinions,  correspondence with public officials,  certificates  provided by your
officers and representatives, and other documents as we have deemed necessary or
advisable for the purposes of rendering the opinions set forth herein.

     Based on the  foregoing,  it is our  opinion  that  upon the  issuance  and
delivery of the Notes in  accordance  with the  Underwriting  Agreement  and the
Indenture,  and receipt by you of the consideration set forth in the Prospectus,
the Notes will be validly  issued and will  constitute  your legal,  valid,  and
binding  obligations except as the same may be limited by (a) general principles
of equity or by bankruptcy, insolvency, reorganization, arrangement, moratorium,
or other laws or equitable  principles  relating to or affecting the enforcement
of creditors' rights generally,  or by equitable principles that limit the right

Arizona Public Service Company
May 7, 2003
Page 2

to specific performance or otherwise limit remedial action or the enforcement of
any security  provided  for the Notes,  and (b) the  qualification  that certain
waivers,  procedures,  remedies,  and  other  provisions  of  the  Notes  may be
unenforceable under or limited by the law of the State of Arizona; however, such
law does not in our opinion  substantially  prevent the practical realization of
the benefits thereof.

     Consent  is  hereby  given  to the  use of  this  opinion  as  part  of the
Registration  Statement,  and to the use of our name wherever it appears in said
Registration Statement and the related Prospectus.

                                        Very truly yours

                                        Snell & Wilmer LLP