EXHIBIT 10b. SYSTEM PURCHASE OPTION AND RATE GUARANTEE



         This System  Purchase  Option and Rate Guarantee (the  "Agreement")  is
made this 25th day of August,  1994, at Las Cruces,  New Mexico, by the City of
Las Cruces, New Mexico (the "City"),  and Southwestern Public Service Company, a
New Mexico corporation ("Southwestern").

                                Recitals

         WHEREAS, El Paso Electric Company ("EPE") owns and operates an electric
utility system serving the City, including  distribution,  subtransmission,  and
transmission facilities, to provide electricity to the citizens of the City (the
"Facility"), and the City is a retail customer of EPE;

         WHEREAS,  on May 23, 1994,  Central and South West Corporation  ("CSW")
issued  a public  statement  projecting  a base  rate  for  customers  receiving
electric  energy from the  Facility  that  contained no increase in its existing
rates before 1998;  then,  beginning in 1998,  CSW may seek a one-time base rate
increase  no  higher  than 6  percent,  with  no  further  increase  until  2002
(collectively, the "Projected Rate");

         WHEREAS,  the City intends to purchase  the  Facility  from EPE through
condemnation  procedures  pursuant to the laws of the State of New Mexico and to
purchase power from  Southwestern  pursuant to the Power Sales Agreement between
the City and Southwestern dated August 22, 1994;

         WHEREAS,  the City  desires  the  exclusive  right and  option to sell,
without  becoming  obligated to sell, the Facility to  Southwestern at an agreed
price and under specified terms and conditions;

         THEREFORE, in consideration of the sum of $10 and other good and
 valuable  consideration,  it is agreed as follows:

                            Grant of Option

                  1.  Southwestern  grants  to the  City the  option  to sell to
Southwestern the Facility it obtains through  condemnation  proceedings pursuant
to the terms of this Agreement (the "Option").








                            Option Period

                  2. The Option to sell the  Facility  shall  commence  when the
City becomes the owner of the Facility and continue for three years  thereafter;
provided,  however, in no event shall the Option be exercisable after January 1,
2002.

                            Exercise of Option

                  3.        The City may exercise the Option by delivering 
 written notice to  Southwestern  as set forth in Paragraph 7 below.

                            Asset Purchase Agreement

                  4. As soon as practicable after the City exercises the Option,
the City and Southwestern shall in good faith negotiate,  execute,  deliver, and
consummate a definitive  asset purchase  agreement  (the  "Purchase  Agreement")
pursuant  to  which   Southwestern  will  purchase  the  Facility  for  a  total
consideration  equal to the  amount  required  to retire  all  outstanding  debt
incurred by the City in acquiring the Facility from EPE and the reasonable costs
incurred by the City in  connection  with the  acquisition  of the Facility from
EPE. In  addition,  Southwestern  shall  charge a total rate which shall be less
than  the  Projected  Rate  and the cost of fuel  EPE  would  bill to  customers
receiving   electric  energy  from  the  Facility.   The  City  shall  grant  to
Southwestern a 25-year franchise,  containing reasonable  performance guarantees
by Southwestern,  to operate the Facility under prudent utility practices at the
usual and customary  franchise fees for similarly  situated electric  utilities.
The  Purchase   Agreement  shall  also  contain   representations,   warranties,
covenants,  conditions, and other terms customary or advisable for a transaction
involving the sale of the Facility and be subject to Section 3-54-1 et seq. NMSA
1978 (1994 Supp.).

                            Automatic Termination

                  5. If the City fails to exercise the Option in accordance with
the terms of this Agreement within the Option period,  the Option and the City's
rights  under this  Agreement  shall  automatically  and  immediately  terminate
without notice.

                           Termination by Southwestern

                  6. Southwestern may terminate the Option and this Agreement at
any time before the City no longer has the right to terminate  the  condemnation
proceedings  by giving the City written  notice (a) if, in  Southwestern's  sole
discretion,  it deems the proposed condemnation award to be excessive, or (b) if
the City obtains  immediate  possession  under Section  42A-1-22 NMSA 1978 (1994
Repl.).  If the City abandons or dismisses  its  condemnation  proceedings  as a
consequence  of  Southwestern's  termination  of the Option and this  Agreement,
Southwestern  will reimburse the City for one-half of its reasonable  litigation
expenses and for any of EPE's damages and litigation expenses which the City may
be  obligated  to pay by final  order of a court  having  jurisdiction  over the
proceeding  pursuant to New  Mexico's  Eminent  Domain Code,  such  expenses and
damages being ascertained as of the date of Southwestern's notice.

                             Notices

                  7. Unless otherwise provided,  any notice, tender, or delivery
to be given by either party to the other may be effected by personal delivery in
writing or by registered or certified  mail,  postage  prepaid,  return  receipt
requested,  and shall be deemed  received as of five days from  mailing.  Mailed
notices  shall be addressed  as set forth  below,  but each party may change its
address by written notice in accordance with this Paragraph.

                                  To the City:

                                  City of Las Cruces, New Mexico
                                  200 N. Church Street (88004)
                                  P.O. Drawer CLC
                                  Las Cruces, New Mexico 88004

                                  Attn:    Bruno Zaldo, City Manager


                                  To Southwestern:

                                  Southwestern Public Service Company
                                  Tyler at Sixth (79101)
                                  P.O. Box 1261
                                  Amarillo, Texas 79170

                                  Attn:  Gary L. Gibson,
                                         Vice President, Marketing

                             Entire Agreement

                  8. This  Agreement  contains  the entire  agreement  between 
the  parties  relating to the Option.  Any oral representations or modifications
concerning the Agreement shall be of no force and effect.

                             Time of the Essence

                  9. Time is of the essence of this Agreement.

                             Amendments

                  10. No change,  amendment,  or  modification of this Agreement
shall be valid or binding unless the change,  amendment,  or  modification is in
writing and is duly signed by each of the parties hereto.

                             Governing Laws

                  11. This Agreement shall be construed under and in accordance
 with the laws of New Mexico.

                              Counterparts

                  12. The  parties may sign any number of  counterparts  of this
Agreement,  and each  fully  signed  counterpart  shall be  deemed  an  original
instrument, but all counterparts together shall constitute only one instrument.

                              Binding Effect

                  13. This  Agreement  shall bind and inure to the benefit of
 the  successors  and assigns of the parties except as expressly provided above.

         IN WITNESS  WHEREOF,  the parties have executed this  Agreement the day
and year first above written.

                                       SOUTHWESTERN PUBLIC SERVICE COMPANY


                                       By:   Coyt Webb
                                             President
ATTEST:


Mary Pullum
Assistant Secretary

(SEAL)


                                      CITY OF LAS CRUCES, NEW MEXICO


                                      By:  Rueben Smith
                                           Mayor
ATTEST:


Karen Stevens
Title: City Clerk

(SEAL)