<PAGE>

                                                                     EXHIBIT 4.5
--------------------------------------------------------------------------------


                                 UNIT AGREEMENT

                                      Among


                             TNP ENTERPRISES, INC.,

                              SW ACQUISITION, L.P.


                                       and


                              THE BANK OF NEW YORK


                              --------------------

                            Dated as of May 26, 2000

                              --------------------


--------------------------------------------------------------------------------
<PAGE>

                  UNIT AGREEMENT dated as of May 26, 2000 among TNP ENTERPRISES,
INC., a Texas corporation (the "Company"), SW ACQUISITION, L.P., a Texas limited
partnership (the "Partnership" and, together with the Company, the "Issuers"),
and The Bank of New York, a New York banking corporation, as Unit Agent,
Transfer Agent and Warrant Agent (in each case, as defined below).

                  WHEREAS, the Company proposes to issue 100,000 shares of its
14 1/2% Senior Redeemable Preferred Stock, $1,000 liquidation preference per
share (the "Shares"), under a Statement of Resolution filed with the Secretary
of State of the State of Texas on May 25, 2000 (the "Statement of Resolution"),
under which The Bank of New York has been named as transfer agent for the Shares
(the "Transfer Agent"), and the Partnership proposes to issue warrants (the
"Warrants") pursuant to a Warrant Agreement dated as of May 26, 2000 between the
Partnership and The Bank of New York, as warrant agent (the "Warrant Agent"),
each Warrant entitling the holder thereof to purchase (at an exercise price of
$.01 per limited partnership interest) a limited partnership interest in the
Partnership (a "Limited Partnership Interest") entitling its holder to receive
the amount a limited partner who had made a $37.5388601 capital contribution (or
0.000035% of total capital contributions as of the original issuance date of the
Warrants) would receive of the residual distributions made to all partners in
accordance with their capital contributions after a return on capital and
preferred distributions are made to the limited partners (other than holders of
Limited Partnership Interests issued upon exercise of the Warrants) and the
general partner, subject to adjustment. The Limited Partnership Interests
issuable upon exercise of the Warrants will provide the holders with the same
rights and obligations as are provided to limited partners, except in certain
cases where rights and obligations apply only to the original limited partners
and except for the right to receive the preferred distributions and the benefits
and obligations under certain tag-along and right of first offer provisions. The
Shares and the Warrants will initially be represented by units (the "Units"),
with each Unit consisting of one Share and one Warrant.

                  WHEREAS, the Issuers, the Transfer Agent and the Warrant Agent
desire to appoint The Bank of New York to act as their agent for the purpose of
issuing certificates ("Unit Certificates") representing the Units and for the
registration of transfers and exchanges thereof. The Bank of New York, in such
capacity, is referred to herein as the "Unit Agent."
<PAGE>

                                      -2-


                  WHEREAS, the Units will be exchangeable for the Shares and the
Warrants represented thereby on the earliest of: (i) 180 days after the original
issuance date of the Units; (ii) the occurrence of a Change of Control (as
defined in the Statement of Resolution); (iii) the occurrence of a Voting Rights
Triggering Event (as such term is defined in the Statement of Resolution); (iv)
the effectiveness of a registration statement with respect to the Shares; and
(v) such earlier date as determined by CIBC World Markets Corp. in its sole
discretion. The date on which an event listed in the preceding sentence occurs
is referred to as the "Separation Date."

                  NOW, THEREFORE, in consideration of the premises and the
mutual agreements herein set forth, the parties hereto agree as follows:

                  SECTION 1.  Appointment of Unit Agent. (a) The Issuers hereby
                              -------------------------
appoint the Unit Agent to act as agent for the Issuers in accordance with and
subject to the terms and conditions set forth in this Agreement, and the Unit
Agent hereby accepts such appointment.

                  (b) The Transfer Agent and the Company hereby appoint the Unit
Agent as registrar for the Shares for so long as the Shares are represented by
the Units. In its capacity as Registrar, the Unit Agent shall have the rights
and obligations provided for such capacities in the Statement of Resolution.

                  (c) The Warrant Agent and the Partnership hereby appoint the
Unit Agent as Authenticating Agent and Registrar (as such terms are defined in
the Warrant Agreement) for the Warrants for so long as the Warrants are
represented by the Units. In its capacity as Authenticating Agent and Registrar,
the Unit Agent shall have the rights and obligations provided for such
capacities in the Warrant Agreement.

                  SECTION 2. Unit Certificates. The Units will initially be
                             -----------------
issued either in global form (the "Global Units"), substantially in the form of
Exhibit A (including footnotes 1 and 2 thereto), or in registered form as
---------
definitive Unit certificates ("Definitive Units"), substantially in the form of
Exhibit A (not including footnotes 1 and 2 thereto). Each Global Unit shall
---------
represent such of the outstanding Units as shall be specified therein and each
shall provide that it shall represent the aggregate Units from time to time
endorsed thereon and that the aggregate amount of outstanding Units represented
thereby may from time to time be reduced or increased, as appropriate. Any
endorsement of a Global unit to reflect

<PAGE>

                                      -3-


the amount of any increase or decrease in the amount of outstanding Units
represented thereby shall be made by the Unit Agent and depositary with respect
to the Global Units (the "Depositary") in accordance with written instructions
given by the holder thereof. The Depository Trust Company shall act as the
Depositary with respect to the Global Units until a successor shall be appointed
by the Issuers and the Unit Agent. Upon written request, a Unit holder may
receive from the Depositary and Unit Agent Definitive Units as set forth in
Section 5 below.

                  SECTION 3. Execution of Unit Certificates. Unit Certificates
                             ------------------------------
shall be signed on behalf of the Company by the Chairman of the Board, its
President or an Executive Officer of the Company and on behalf of the
Partnership by the manager (the "Manager") of SW II Acquisition LLC (each an
"Executing Officer"), a Texas limited liability company and general partner of
SW I Acquisition GP, L.P., a Texas limited partnership and general partner of
the Partnership. Each such signature upon the Unit Certificates may be in the
form of a facsimile signature of the Executing Officer and may be imprinted or
otherwise reproduced on the Unit Certificates.

                  In case any Executing Officer of the Company or the
Partnership who shall have signed any of the Unit Certificates shall cease to be
an Executing Officer before the Unit Certificates so signed shall have been
authenticated by the Unit Agent, or disposed of by the Company or the
Partnership, such Unit Certificates nevertheless may be authenticated and
delivered or disposed of as though such person had not ceased to be an Executing
Officer of the Company or the Partnership; and any Unit Certificate may be
signed on behalf of the Company or the Partnership by any person who, at the
actual date of the execution of such Unit Certificate, shall be a proper
Executing Officer of the Company or the Partnership to sign such Unit
Certificate, although at the date of the execution of this Unit Agreement or the
authentication of any such Unit Certificates any such person was not such
officer or manager.

                  SECTION 4. Registration and Authentication. The Unit Agent,
                             -------------------------------
on behalf of the Issuers, shall number and register the Unit Certificates in a
register as they are issued by the Issuers. Unit Certificates shall be manually
authenticated by the Unit Agent and shall not be valid for any purpose unless so
authenticated. Unit Certificates shall be dated the date of authentication by
the Unit Agent. The Unit Agent shall, upon written instructions of the Chairman
of the Board, the President or any Vice President of the Company and the Manager
<PAGE>

                                      -4-

specifying the amount of Units to be authenticated, whether the Units are to be
Global Units or Definitive Units, and such other information as the Unit Agent
may request, initially authenticate and deliver not more than 100,000 Units and
shall thereafter authenticate and deliver Units as otherwise provided in this
Agreement.
                  The Issuers and the Unit Agent may deem and treat the
registered holder(s) of the Unit Certificates as the absolute owner(s) thereof
(notwithstanding any notation of ownership or other writing thereon made by
anyone) for all purposes, and neither the Issuers nor the Unit Agent shall be
affected by any notice to the contrary.

                  SECTION 5.  Registration of Transfers and Exchanges.
                              ---------------------------------------

                  (a)   Transfer and Exchange of Definitive Units.  Prior to the
                        -----------------------------------------
Separation  Date, when  Definitive  Units are presented to the Unit Agent with a
request:

                  (i)   to register the transfer of the Definitive Units; or

                  (ii)  to exchange such Definitive Units for an equal number of
                        Definitive Units of other authorized denominations,

the Unit Agent shall register the transfer or make the exchange as requested if
the requirements under this Agreement as set forth in this Section 5 for such
transactions are met; provided, however, that the Definitive Units presented or
                      --------  -------
surrendered for registration of transfer or exchange:

         (x)      shall be duly endorsed or accompanied by a written instruction
                  of transfer in form satisfactory to the Unit Agent, duly
                  executed by the holder thereof or by his attorney, duly
                  authorized in writing; and

         (y)      in the case of Units the offer and sale of which have not been
                  registered under the Act (as defined below) and are presented
                  for registration of transfer or exchange prior to (I) the date
                  which is two years after the later of the date of original
                  issue and the last date on which the Issuers or any affiliate
                  of the Issuers was the owner of such Unit, or any predecessor
                  thereto, and (II) such later date, if any, as may be required
                  by any subsequent change in applicable law,
<PAGE>

                                      -5-


                  such Units shall be accompanied,  by the following  additional
                  information and documents, as applicable:

                  (A) if such Unit is being delivered to the Unit Agent by the
                      registered holder for registration in the name of such
                      holder, without transfer, a certification from such holder
                      to that effect (in substantially the form of Exhibit B
                                                                   ---------
                      hereto);

                  (B) if such Unit is being transferred to a Qualified
                      Institutional Buyer (as defined in Rule 144A under the
                      Securities Act of 1933, as amended (the "Act") in
                      accordance with Rule 144A under the Act, a certification
                      to that effect (in substantially the form of Exhibit B
                                                                   ---------
                      hereto);

                  (C) if such Unit is being transferred (I) to an institutional
                      "accredited investor" within the meaning of subparagraph
                      (a)(1), (a)(2), (a)(3) or (a)(7) of Rule 501 under the Act
                      or (II) pursuant to an exemption from registration in
                      accordance with Rule 144 under the Act or (III) pursuant
                      to a private placement exemption from the registration
                      requirements of the Act (in the case of clauses (I), (II)
                      and (III) based on an opinion of counsel if the Unit Agent
                      so requests or if the Issuers so request and notify the
                      Unit Agent), a certification to that effect (in
                      substantially the form of Exhibit B hereto) and a
                                                ---------
                      certificate from the applicable transferee (in
                      substantially the form of Exhibit C hereto);
                                                ---------
                  (D  if such Unit is being transferred pursuant to an
                      exemption from registration in accordance with Rule
                      904 under the Act (and based on an opinion of counsel
                      if the Unit Agent so requests or if the Issuers so
                      request and notify the Unit Agent), a certification
                      to that effect (in substantially the forms of Exhibit
                                                                    -------
                      B and Exhibit D hereto); or
                      -     ---------
                  (E) if such Unit is being transferred in reliance on
                      another exemption from the registration requirements
                      of the Act, a certification to that effect (in
                      substantially the form of Exhibit B hereto) and an
                                                ---------
                      opinion of counsel reasonably acceptable to the
                      Issuers or the Unit Agent to the effect
<PAGE>

                                      -6-

                      that such transfer is in compliance with the Act.

          (b) Restrictions on Exchange and Transfer of a Definitive Unit for a
              ----------------------------------------------------------------
Beneficial Interest in a Global Unit. A Definitive Unit may not be exchanged for
------------------------------------
a beneficial interest in a Global Unit except upon satisfaction of the
requirements set forth below. Upon receipt by the Unit Agent of a Definitive
Unit, duly endorsed or accompanied by appropriate instruments of transfer, in
form satisfactory to the Unit Agent, together with:

          (A) certification from the holder thereof (substantially in the form
              of Exhibit B hereto), that such Definitive Unit is being
                 ---------
              transferred to a "Qualified Institutional Buyer" (as defined in
              Rule 144A under the Act) in accordance with Rule 144A under the
              Act; and

          (B) written instructions directing the Unit Agent to make, or to
              direct the Depositary to make, an endorsement on the Global Unit
              to reflect an increase in the aggregate amount of the Units
              represented by the Global Unit,

then the Unit Agent shall cancel such Definitive Unit and cause, or direct the
Depositary to cause, in accordance with the standing instructions and procedures
existing between the Depositary and the Unit Agent, the number of Units
represented by the Global Unit to be increased accordingly. If no Global Unit is
then outstanding, the Issuers shall issue and the Unit Agent shall authenticate
a new Global Unit in the appropriate amount.

          (c) Transfer and Exchange of Global Units. The transfer and exchange
              --------------------------------------
of Global Units or beneficial interests therein shall be effected through the
Depositary, in accordance with this Unit Agreement (including the restrictions
on transfer set forth herein) and the procedures of the Depositary therefor.

          (d) Exchange of a Beneficial Interest in a Global Unit for a
              --------------------------------------------------------
Definitive Unit.
---------------

      (i) Prior to the Separation Date, to the extent permitted by law, any
          person having a beneficial interest in a Global Unit may upon request
          exchange such beneficial interest for a Definitive Unit. Upon receipt
          by the
<PAGE>

                                      -7-

          Unit Agent of written instructions (or such other form of instructions
          as is customary for the Depositary) from the Depositary or its nominee
          on behalf of any person having a beneficial  interest in a Global Unit
          and, the following additional information and documents:


          (A)    If such beneficial interest is being delivered to the person
                 designated by the Depositary as being the beneficial owner, a
                 certification from such person to that effect (in substantially
                 the form of Exhibit B hereto);
                             ---------

          (B)    if such beneficial interest is being transferred to a Qualified
                 Institutional Buyer (as defined in Rule 144A under the Act) in
                 accordance with Rule 144A under the Act or pursuant to an
                 effective registration statement under the Act, a certification
                 to that effect (in substantially the form of Exhibit B hereto);
                                                              ---------

          (C)    if such beneficial interest is being transferred (I) to an
                 institutional "accredited investor" within the meaning of
                 subparagraph (a)(1), (a)(2), (a)(3) or (a)(7) of Rule 501 under
                 the Act or (II) pursuant to an exemption from registration in
                 accordance with Rule 144 under the Act or (III) pursuant to a
                 private placement exemption from the registration requirements
                 of the Act (in the case of clauses (I), (II) and (III), based
                 on an opinion of counsel if the Unit Agent so requests or if
                 the Issuers so request and notify the Unit Agent), delivery of
                 a Certificate of Transfer (in substantially the form of
                 Exhibit B hereto) and a certification from the applicable
                 ---------
                 transferee (in substantially the form of Exhibit C hereto);
                                                          ---------

          (D)    if such beneficial interest is being transferred pursuant to an
                 exemption from registration in accordance with Rule 904 under
                 the Act (and based on an opinion of counsel if the Unit Agent
                 so requests or if the Issuers so request and notify the Unit
                 Agent), a certification to that effect (in substantially the
                 forms of Exhibit B and Exhibit D hereto); or
                          ---------     ---------
<PAGE>

                                      -8-



          (E)    if such beneficial interest is being transferred in reliance on
                 another exemption from the registration requirements of the Act
                 (and based on an opinion of counsel if the Unit Agent so
                 requests or if the Issuers so request and notify the Unit
                 Agent), a certification to that effect (in substantially the
                 form of Exhibit B hereto),
                         ---------

          then the Unit Agent will cause, in accordance with the standing
          instructions and procedures existing between the Depositary and the
          Unit Agent, the aggregate amount of the Global Unit to be reduced and,
          following such reduction, the Issuers will execute and the Unit Agent
          will authenticate and deliver to the transferee at the principal
          office of the Unit Agent a Definitive Unit.

          (ii)  Definitive Units issued in exchange for a beneficial interest in
                a Global Unit pursuant to this Section 5(d) shall be registered
                in such names and in such authorized denominations as the
                Depositary, pursuant to instructions from its direct or indirect
                participants or otherwise, shall instruct in writing the Unit
                Agent. The Unit Agent shall deliver at the principal office of
                the Unit Agent such Definitive Units to the persons in whose
                names such Units are so registered.

          (e)   Restrictions on Transfer and Exchange of Global Units.
                -----------------------------------------------------
Notwithstanding any other provisions of this Unit Agreement (other than the
provisions set forth in subsection (f) of this Section 5), a Global Unit may not
be transferred as a whole except by the Depositary to a nominee of the
Depositary or by a nominee of the Depositary to the Depositary or another
nominee of the Depositary or by the Depositary or any such nominee to a
successor Depositary or a nominee of such successor Depositary.

          (f)   Authentication of Definitive Units in Absence of Depositary.
                -----------------------------------------------------------
If at any time:

                 (i)   the Depositary for the Units notifies the Issuers that
                       the Depositary is unwilling or unable to continue as
                       Depositary for the Global Unit and a successor Depositary
                       for the Global Unit is not appointed by the Issuers
                       within 90 days after delivery of such notice; or
<PAGE>

                                      -9-

                 (ii)  the Issuers, at their sole discretion, notify the Unit
                       Agent in writing that they elect to cause the issuance of
                       Definitive Units under this Unit Agreement,

then the Issuers will execute, and the Unit Agent, upon written instruction of
the Chairman of the Board, President or any Vice President of the Company and
the Manager, shall authenticate and deliver, Definitive Units, in an aggregate
number equal to the aggregate number of Units represented by the Global Unit, in
exchange for such Global Unit.

                 (g)   Legends.
                       -------

                 (i)   Except as permitted by the following paragraph (ii), each
                       Unit Certificate evidencing the Global Units and the
                       Definitive Units (and all Units issued in exchange
                       therefor or substitution thereof) shall bear a legend
                       substantially to the following effect:

          "THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE U.S. SECURITIES ACT
         OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND, ACCORDINGLY, MAY NOT
         BE OFFERED OR SOLD WITHIN THE UNITED STATES OR TO, OR FOR THE ACCOUNT
         OR BENEFIT OF, U.S. PERSONS EXCEPT AS SET FORTH BELOW. BY ITS
         ACQUISITION HEREOF, THE HOLDER (1) REPRESENTS THAT (A) IT IS A
         "QUALIFIED INSTITUTIONAL BUYER" (AS DEFINED IN RULE 144A UNDER THE
         SECURITIES ACT) OR (B) IT IS NOT A U.S. PERSON AND IS ACQUIRING THIS
         SECURITY IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 UNDER
         THE SECURITIES ACT, (2) AGREES THAT IT WILL NOT WITHIN TWO YEARS AFTER
         THE ORIGINAL ISSUANCE OF THIS SECURITY RESELL OR OTHERWISE TRANSFER
         THIS SECURITY, EXCEPT (A) TO THE ISSUER OR ANY SUBSIDIARY THEREOF, (B)
         INSIDE THE UNITED STATES TO A QUALIFIED INSTITUTIONAL BUYER IN
         COMPLIANCE WITH RULE 144A PROMULGATED UNDER THE SECURITIES ACT, (C)
         INSIDE THE UNITED STATES TO AN ACCREDITED INVESTOR THAT, PRIOR TO SUCH
         TRANSFER, FURNISHES (OR HAS FURNISHED ON ITS BEHALF BY A U.S.
         BROKER-DEALER) TO THE UNIT AGENT A SIGNED LETTER CONTAINING CERTAIN
         REPRESENTATIONS AND AGREEMENTS RELATING TO THE RESTRICTIONS ON TRANSFER
         OF THIS SECURITY (THE FORM OF WHICH LETTER CAN BE OBTAINED FROM THE
         UNIT AGENT FOR THIS SECURITY), (D) OUTSIDE THE UNITED STATES IN AN
         OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 UNDER THE SECURITIES
<PAGE>

                                      -10-

         ACT, (IF AVAILABLE) (E) PURSUANT TO THE EXEMPTION FROM REGISTRATION
         PROVIDED BY RULE 144 PROMULGATED UNDER THE SECURITIES ACT (IF
         AVAILABLE) OR (F) PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER
         THE SECURITIES ACT AND (3) AGREES THAT IT WILL GIVE TO EACH PERSON TO
         WHOM THIS SECURITY IS TRANSFERRED A NOTICE SUBSTANTIALLY TO THE EFFECT
         OF THIS LEGEND. IN CONNECTION WITH ANY TRANSFER OF THIS SECURITY WITHIN
         TWO YEARS AFTER THE ORIGINAL ISSUANCE OF THIS SECURITY, IF THE PROPOSED
         TRANSFEREE IS AN ACCREDITED INVESTOR, THE HOLDER MUST, PRIOR TO SUCH
         TRANSFER, FURNISH TO THE UNIT AGENT AND THE ISSUER SUCH CERTIFICATIONS,
         LEGAL OPINIONS OR OTHER INFORMATION AS EITHER OF THEM MAY REASONABLY
         REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING MADE PURSUANT TO AN
         EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION
         REQUIREMENTS OF THE SECURITIES ACT. AS USED HEREIN, THE TERMS "OFFSHORE
         TRANSACTION," "UNITED STATES" AND "U.S. PERSONS" HAVE THE MEANINGS
         GIVEN TO THEM BY REGULATION S UNDER THE SECURITIES ACT."

               (ii)      Upon any sale or transfer of a Unit pursuant to Rule
                         144 under the Act or an effective registration
                         statement under the Act:

                         (A)  in the case of any Unit that is a Definitive Unit,
                              the Unit Agent shall permit the registered holder
                              thereof to exchange such Unit for a Definitive
                              Unit that does not bear the legend set forth in
                              clause (i) above and rescind any restriction on
                              the transfer of such Unit; and

               (B)       any such Unit represented by a Global Unit shall not be
                         required to bear the legend set forth in clause (i)
                         above but shall continue to be subject only to the
                         provisions of Section 5(c) hereof; provided, however,
                                                            --------  -------
                         that with respect to any request for an exchange of a
                         Unit that is represented by a Global Unit for a
                         Definitive Unit that does not bear the legend set forth
                         above, which request is made in reliance upon Rule 144
                         under the Act (and based on an opinion of counsel if
                         the Issuers so request and notify the Unit Agent),
                         the registered holder thereof shall certify in
<PAGE>

                                      -11-

                         writing to the Unit Agent that such request is being
                         made pursuant to Rule 144 under the Act (such
                         certification to be substantially in the form of
                         Exhibit B hereto).
                         ---------

               (h)  Cancellation of a Global Unit. At such time as all
                    -----------------------------
beneficial interests in a Global Unit have either been exchanged for Definitive
Units, redeemed, repurchased or cancelled, such Global Unit shall be returned to
or retained and cancelled by the Unit Agent.

               (i)  Obligations with Respect to Transfers and Exchanges of
                    ------------------------------------------------------
Definitive Units.
----------------

               (i)    Prior to the Separation Date, to permit registrations of
                      transfers and exchanges, the Issuers shall execute, and
                      the Unit Agent is hereby authorized to authenticate in
                      accordance with provisions of Section 4 and this Section
                      5, Definitive Units and Global Units as required pursuant
                      to the provisions of this Section 5.

               (ii)   All Definitive Units and Global Units issued upon any
                      registration of transfer or exchange of Definitive Units
                      or Global Units shall be the valid obligations of the
                      Issuers, entitled to the same benefits under this Unit
                      Agreement as the Definitive Units or Global Units
                      surrendered upon the registration of transfer or exchange.

               (iii)  Prior to due presentment for registration of transfer of
                      any Unit, the Unit Agent and the Issuers may deem and
                      treat the person in whose name any Unit is registered as
                      the absolute owner of such Unit, and neither the Unit
                      Agent nor the Issuers shall be affected by notice to the
                      contrary.

               (iv)   No service charge shall be made to a holder for any
                      registration of transfer or exchange.

               SECTION 6. Separation of the Shares and the Warrants. After the
                          -----------------------------------------
Separation Date, the Shares and the Warrants represented by the Units shall be
separately transferable. Upon presentation after the Separation Date of any Unit
Certificate for exchange for Warrants and Shares or for registration of transfer
or otherwise, (i) the Unit Agent shall notify the Transfer Agent and the Warrant
Agent of the number of Units
<PAGE>

                                     -12-


so presented, the registered owner thereof, such owner's registered address, the
nature of any legends or restrictive endorsements set forth on such Unit
Certificate and any other information provided by the registered holder thereof
in connection therewith, (ii) the Transfer Agent, if the requirements of the
Statement of Resolution for such transaction are met, shall promptly
authenticate, register and deliver a new Share or Shares equal in aggregate
liquidation preference to the Shares represented by such Unit Certificate in
accordance with the direction of such registered holder and (iii) the Warrant
Agent, if the requirements for such transaction are met, shall promptly
authenticate, register and deliver a new Warrant certificate or certificates for
the number of Warrants previously represented by such Unit Certificate in
accordance with the directions of such registered holder. The Warrant Agent and
the Transfer Agent will notify the Unit Agent of any additional requirements in
connection with a particular transfer or exchange.

          Following the Separation Date, no Unit Certificates shall be issued
upon registration of transfer or exchange of Unit Certificates, or otherwise.

          SECTION 7.     Rights of Unit Holders.  The registered owner of a Unit
                         ----------------------
Certificate shall have all the rights and privileges of a registered owner of
the liquidation preference of Shares represented thereby and the number of
Warrants represented thereby and shall be treated as the registered owner
thereof for all purposes.

          SECTION 8.     Unit Agent.  The Unit Agent undertakes the duties and
                         ----------
obligations imposed by this Agreement upon the following terms and conditions,
by which the Issuers and the holders of Units, by their acceptance thereof,
shall be bound:

          (a) The statements contained herein and in the Unit Certificates shall
     be taken as statements of the Issuers, and the Unit Agent assumes no
     responsibility for the correctness of any of the same except such as
     describe the Unit Agent.  The Unit Agent assumes no responsibility with
     respect to the distribution of the Unit Certificates except as herein
     otherwise specifically provided.

          (b) The Unit Agent shall not be responsible for any failure of the
     Issuers to comply with any of the covenants in this Agreement, the Unit
     Certificates, the Warrant Agreement or the Statement of Resolution.
<PAGE>

                                     -13-


          (c) The Unit Agent may consult at any time with counsel satisfactory
     to it (who may be counsel for the Issuers) and the Unit Agent shall incur
     no liability or responsibility to the Issuers or to any holder of any Unit
     in respect of any action taken, suffered or omitted by it hereunder in good
     faith and in accordance with the opinion or the advice of such counsel.

          (d) The Unit Agent shall incur no liability or responsibility to the
     Issuers or to any holder of any Unit Certificate for any action taken in
     reliance on any Unit Certificate, certificate of shares, notice,
     resolution, waiver, consent, order, certificate, or other paper, document
     or instrument believed by the Unit Agent to be genuine and to have been
     signed, sent or presented by the proper party or parties.

          (e) The Issuers agree to pay to the Unit Agent compensation for all
     services rendered by the Unit Agent in connection with the execution and
     performance of this Agreement at such rates as have been separately agreed
     to in writing by the Issuers and the Unit Agent and to reimburse the Unit
     Agent for all expenses, taxes and governmental charges and other charges of
     any kind and nature incurred by the Unit Agent in the execution and
     performance of this Agreement.  The Issuers shall indemnify the Unit Agent
     and its agents and save each of them harmless against any and all losses,
     damages, claims, liabilities and expenses, including judgments, costs and
     counsel fees and expenses, including taxes (other than taxes based upon,
     measured by or determined by the income of the Unit Agent) and the costs
     and expenses of investigating or defending any claim of such liability, for
     any action taken or omitted by the Unit Agent or its agents in the
     execution of and performance of its obligations under this Agreement except
     as a result of its negligence or bad faith.  The Unit Agent shall notify
     the Issuers promptly of any claim for which it may seek indemnity; provided
                                                                        --------
     that failure by the Unit Agent to so notify the Issuers shall not relieve
     their obligations hereunder.  The Issuers shall defend the claim and the
     Unit Agent shall cooperate in the defense.  The Unit Agent may have
     separate counsel and the Issuers shall pay the reasonable fees and expenses
     of such counsel.  The Issuers need not pay for any settlement made without
     their consent, which consent shall not be unreasonably withheld.  The
     provisions of this paragraph (e) shall survive the termination of this
     Agreement/
<PAGE>

                                     -14-


          (f) The Unit Agent shall be under no obligation to institute any
     action, suit or legal proceeding or to take any other action likely to
     involve expense unless the Company or one or more registered holders of
     Unit Certificates shall furnish the Unit Agent with security and indemnity
     reasonably satisfactory to it for any costs and expenses which may be
     incurred, but this provision shall not affect the power of the Unit Agent
     to take such action as it may consider proper, whether with or without any
     such security or indemnity.  All rights of action under this Agreement or
     under any of the Units may be enforced by the Unit Agent without the
     possession of any of the Unit Certificates or the production thereof at any
     trial or other proceeding relative thereto, and any such action, suit or
     proceeding instituted by the Unit Agent shall be brought in its name as
     Unit Agent and any recovery of judgment shall be for the ratable benefit of
     the registered holders of the Units, as their respective rights or
     interests may appear.

          (g) The Unit Agent, and any stockholder, director, officer or employee
     of it, may buy, sell or deal in any of the Units or other securities of the
     Issuers or become pecuniarily interested in any transaction in which the
     Issuers may be interested, or contract with or lend money to the Issuers or
     otherwise act as fully and freely as though it were not the Unit Agent
     under this Agreement.  Nothing herein shall preclude the Unit Agent from
     acting in any other capacity for the Issuers or for any other legal entity.

          (h) The Unit Agent shall act hereunder solely as agent for the
     Issuers, its duties shall be determined solely by the provisions hereof and
     no implied covenants or obligations shall be read into this Agreement
     against the Unit Agent.  The Unit Agent shall not be liable for anything
     which it may do or refrain from doing in connection with this Agreement
     except for its own negligence or bad faith.

          (i) In the absence of bad faith on its part, the Unit Agent may
     conclusively rely, as to the truth of the statements and the correctness of
     the opinions expressed therein, upon certificates or opinions furnished to
     the Unit Agent and conforming to the requirements of this Agreement.
     However, in the case of any certificates or opinions which by any provision
     hereof are specifically required to be furnished to the Unit Agent, the
     Unit Agent
<PAGE>

                                     -15-

     shall examine the certificates and opinions to determine whether or not
     they conform to the requirements of this Agreement.

          (j) The Unit Agent may rely and shall be fully protected in relying
     upon any document believed by it to be genuine and to have been signed or
     presented by the proper person.  The Unit Agent need not investigate any
     fact or matter stated in the documents.

          (k) The Unit Agent may act through agents and shall not be responsible
     for the misconduct or negligence of any agent appointed and monitored in
     good faith and with due care.

          (l) The Issuers will perform, execute, acknowledge and deliver or
     cause to be performed, executed, acknowledged or delivered all such further
     acts, instruments and assurances as may reasonably be required by the Unit
     Agent in order to enable it to carry out or perform its duties under this
     Agreement.

          (m) Whenever in the administration of this Agreement the Unit Agent
     shall deem it desirable that a matter be proved or established prior to
     taking, suffering or omitting any action hereunder, the Unit Agent (unless
     other evidence be herein specifically prescribed) may, in the absence of
     bad faith on its part, conclusively rely upon an officers' certificate of
     the Company or a similar certificate of the Manager.

          (n) The rights, privileges, protections, immunities and benefits given
     to the Unit Agent including, without limitation, its right to be
     indemnified, are extended to, and shall be enforceable by, the Unit Agent
     in each of its capacities hereunder, and to each agent, custodian and other
     person employed to act hereunder.

          (o) The Unit Agent may request that the Company deliver an officers'
     certificate and that the Partnership delivers a similar certificate of the
     Manager setting forth the names of individuals and/or titles authorized at
     such time to take specified actions pursuant to this Agreement, which
     officers' certificate or similar certificate of the Manager, may be signed
     by any person authorized to sign such a certificate, including any person
     specified as so authorized in any such certificate previously delivered and
     not superseded.
<PAGE>

                                     -16-


          SECTION 9.     Change of Unit Agent.  The Unit Agent may resign at any
                         --------------------
time by so notifying the Issuers.  If the Unit Agent shall resign or become
incapable of acting as Unit Agent, the Issuers shall appoint a successor to such
Unit Agent.  If the Issuers shall fail to make such appointment within a period
of 30 days after it has been notified in writing of such incapacity or
resignation by the Unit Agent or by the registered holder of a Unit Certificate,
then the registered holder of any Unit Certificate may apply to any court of
competent jurisdiction for the appointment of a successor to the Unit Agent at
the expense of the Issuers.  Pending appointment of a successor to such Unit
Agent, either by the Issuers or by such a court, the duties of the Unit Agent
shall be carried out by the Issuers.  After appointment, the successor to the
Unit Agent shall be vested with the same powers, rights, duties and
responsibilities as it if had been originally named as Unit Agent without
further act or deed; but the former Unit Agent, after the payment of all
outstanding amounts owed to it hereunder, shall deliver and transfer to the
successor to the Unit Agent any property at the time held by it hereunder and
execute and deliver any further assurance, conveyance, act or deed necessary for
such purpose.  Failure to give any notice provided for in this Section 9,
however, or any defect therein, shall not affect the legality or validity of the
appointment of a successor to the Unit Agent.  The provisions of Section 8 with
respect to any Unit Agent shall survive such Unit Agent's resignation or removal
and the termination of this Agreement.

          SECTION 10.    Successor Unit Agent by Merger, Etc.  If the Unit Agent
                         -----------------------------------
consolidates with, merges or converts into, or transfers all or substantially
all of its corporate trust business to, another corporation, the resulting,
surviving or transferee corporation without any further act shall, if such
resulting, surviving or transferee corporation is otherwise eligible hereunder,
be the successor Unit Agent.

          SECTION 11.    Notices to the Issuers and Unit Agent, Transfer Agent
                         -----------------------------------------------------
and Warrant Agent.  Any notice or demand authorized by this Agreement to be
-----------------
given or made to or on the Issuers shall be sufficiently given or made when and
if telecopied to the number indicated below or deposited in the mail, first
class or registered, postage paid, addressed (until another telecopy number or
address is filed in writing by the Issuers with the Unit Agent, the Transfer
Agent and the Warrant Agent), as follows:
<PAGE>

                                     -17-


          SW Acquisition, L.P.
          c/o Laurel Hill Capital Partners LLC
          2 Robbins Lane, Suite 201
          Jericho, New York  11753
          Facsimile No.:  (516) 933-3108
          Attention:  Kathleen Marion

          With a copy to:

          Milbank, Tweed, Hadley and McCloy LLP
          1 Chase Manhattan Plaza
          New York, New York  10005
          Facsimile No.: (212) 530-5219
          Attention:  M. Douglas Dunn, Esq.

          In case the Issuers shall fail to maintain such office or shall fail
to give such notice of any change in the location thereof, presentations may be
made and notices and demands may be served at the principal office of the Unit
Agent.

          Any notice pursuant to this Agreement to be given by the Issuers or by
registered holder(s) of any Unit Certificate to the Unit Agent, the Transfer
Agent or the Warrant Agent shall be sufficiently given when and if telecopied to
the number indicated below or deposited in the mail, first class or registered,
postage prepaid, addressed (until another telecopy number or address is filed in
writing by the Unit Agent, the Transfer Agent and the Warrant Agent with the
Issuers), as follows:

          The Bank of New York
          101 Barclay Street, Floor 21 West
          New York, New York  10286
          Facsimile No.:  (212) 815-5915
          Attention:  Corporate Trust Trustee Administration

          Any notice to be mailed to a registered holder of Units shall be
mailed to each holder at its address as it appears on the register of Units
maintained by the Unit Agent.  Copies of any such communication shall also be
mailed to the Unit Agent, the Transfer Agent and the Warrant Agent.  The Unit
Agent shall furnish the Issuers, the Transfer Agent or the Warrant Agent
promptly when requested with a list of registered holders of Units for the
purpose of mailing any notice or communication to the registered holders of the
Units, the Shares or the Warrants and at such other times as may be reasonably
requested.
<PAGE>

                                     -18-


          SECTION 12.    Supplements and Amendments.  The Issuers and the Unit
                         --------------------------
Agent may from time to time supplement or amend this Agreement without the
approval of any registered holders of Units in order to cure any ambiguity or to
correct or supplement any provision contained herein which may be defective or
inconsistent with any other provision herein, or to make any other provisions in
regard to matters or questions arising hereunder which the Issuers, the Transfer
Agent, the Warrant Agent and the Unit Agent may deem necessary or desirable and
which shall not, as evidenced by an opinion of counsel delivered to the Unit
Agent, the Transfer Agent and the Warrant Agent, in any way adversely affect the
interests of the registered holders of Units.  Any amendment or supplement to
this Agreement that has a material adverse effect on the interests of Unit
holders shall require the written consent of the registered holders of not less
than a majority of the outstanding Units.  Each of the Unit Agent, the Transfer
Agent and the Warrant Agent shall be entitled to receive and, subject to Section
8 shall be fully protected in relying upon an officers' certificate and opinion
of counsel as conclusive evidence that any such amendment or supplement is
authorized or permitted hereunder, that it is not inconsistent herewith, and
that it will be valid and binding upon the Issuers in accordance with its terms.
The Issuers may not sign any amendment or supplement until the board of
directors of the Company and the Manager approves it.

          SECTION 13.    Successors.  All the covenants and provisions of this
                         ----------
Agreement by or for the benefit of the Issuers, the Transfer Agent, the Warrant
Agent or the Unit Agent shall bind and inure to the benefit of their respective
successors and assigns hereunder.

          SECTION 14.    Governing Law. THIS AGREEMENT AND EACH UNIT CERTIFICATE
                         -------------
ISSUED HEREUNDER SHALL BE DEEMED TO BE A CONTRACT MADE UNDER THE LAWS OF THE
STATE OF NEW YORK, WITHOUT REGARD TO CONFLICTS OF LAW PRINCIPLES.

          SECTION 15.    Benefits of This Agreement.  Nothing in this Agreement
                         --------------------------
shall be construed to give to any person or corporation other than the Issuers,
the Transfer Agent, the Warrant Agent, the Unit Agent and the registered holders
of the Units any legal or equitable right, remedy or claim under this Agreement;
but this Agreement shall be for the sole and exclusive benefit of the Issuers,
the Transfer Agent, the Warrant Agent, the Unit Agent and the registered holders
of the Unit Certificates.
<PAGE>

                                     -19-


          SECTION 16.    Counterparts.  This Agreement may be executed in any
                         ------------
number of counterparts and each of such counterparts shall for all purposes be
deemed to be an original, and all such counterparts shall together constitute
but one and the same instrument.

          SECTION 17.    Headings.  The headings in this Agreement are for
                         --------
convenience of reference only and shall not limit or otherwise affect the
meaning of any provision hereof.

          SECTION 18.    Severability.  The provisions of this Unit Agreement
                         ------------
are severable, and if any clause or provision shall be held invalid, illegal or
unenforceable in whole or in part in any jurisdiction, then such invalidity or
unenforceability shall affect in that jurisdiction only such clause or
provision, or part thereof, and shall not in any manner affect such clause or
provision in any other jurisdiction or any other clause or provision of this
Unit Agreement in any jurisdiction.
<PAGE>

                                      S-1


          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be duly executed, as of the day and year first above written.


                                   TNP ENTERPRISES, INC.

                                   By:__________________________________
                                      Name:
                                      Title:


                                   SW ACQUISITION, L.P.

                                   By:  SW I ACQUISITION GP, L.P.,
                                           a Texas limited partnership
                                           and its general partner

                                   By:  SW II ACQUISITION LLC, a Texas
                                           limited liability company and
                                           its general partner

                                   By:___________________________________
                                      Name:  William J. Catacosinos
                                      Title:  Manager
<PAGE>

                                      S-2


                                   THE BANK OF NEW YORK, as
                                   Unit Agent


                                   By:__________________________________
                                      Name:
                                      Title:


                                   THE BANK OF NEW YORK, as
                                      Transfer Agent

                                   By:__________________________________
                                      Name:
                                      Title:


                                   THE BANK OF NEW YORK, as
                                     Warrant Agent


                                   By:__________________________________
                                      Name:
                                      Title:
<PAGE>

                                                                       EXHIBIT A
                                                                       ---------
                              [FORM OF SECURITY]
                              ------------------

          "THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE U.S.
          SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"),
          AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD WITHIN THE
          UNITED STATES OR TO, OR FOR THE ACCOUNT OR BENEFIT OF, U.S.
          PERSONS EXCEPT AS SET FORTH BELOW. BY ITS ACQUISITION
          HEREOF, THE HOLDER (1) REPRESENTS THAT (A) IT IS A
          "QUALIFIED INSTITUTIONAL BUYER" (AS DEFINED IN RULE 144A
          UNDER THE SECURITIES ACT) OR (B) IT IS NOT A U.S. PERSON AND
          IS ACQUIRING THIS SECURITY IN AN OFFSHORE TRANSACTION IN
          COMPLIANCE WITH RULE 904 UNDER THE SECURITIES ACT, (2)
          AGREES THAT IT WILL NOT WITHIN TWO YEARS AFTER THE ORIGINAL
          ISSUANCE OF THIS SECURITY RESELL OR OTHERWISE TRANSFER THIS
          SECURITY, EXCEPT (A) TO THE ISSUERS OR ANY SUBSIDIARY
          THEREOF, (B) INSIDE THE UNITED STATES TO A QUALIFIED
          INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A PROMULGATED
          UNDER THE SECURITIES ACT, (C) INSIDE THE UNITED STATES TO AN
          ACCREDITED INVESTOR THAT, PRIOR TO SUCH TRANSFER, FURNISHES
          (OR HAS FURNISHED ON ITS BEHALF BY A U.S. BROKER-DEALER) TO
          THE UNIT AGENT A SIGNED LETTER CONTAINING CERTAIN
          REPRESENTATIONS AND AGREEMENTS RELATING TO THE RESTRICTIONS
          ON TRANSFER OF THIS SECURITY (THE FORM OF WHICH LETTER CAN
          BE OBTAINED FROM THE UNIT AGENT FOR THIS SECURITY), (D)
          OUTSIDE THE UNITED STATES IN AN OFFSHORE TRANSACTION IN
          COMPLIANCE WITH RULE 904 UNDER THE SECURITIES ACT (IF
          AVAILABLE), (E) PURSUANT TO THE EXEMPTION FROM REGISTRATION
          PROVIDED BY RULE 144 PROMULGATED UNDER THE SECURITIES ACT
          (IF AVAILABLE) OR (F) PURSUANT TO AN EFFECTIVE REGISTRATION
          STATEMENT UNDER THE SECURITIES ACT AND (3) AGREES THAT IT
          WILL GIVE TO EACH PERSON TO WHOM THIS SECURITY IS
          TRANSFERRED A NOTICE SUBSTANTIALLY TO THE EFFECT OF THIS
          LEGEND. IN CONNECTION WITH ANY TRANSFER OF THIS SECURITY
          WITHIN TWO YEARS AFTER THE ORIGINAL ISSUANCE OF THIS
          SECURITY, IF THE PROPOSED TRANSFEREE IS AN ACCREDITED
          INVESTOR, THE HOLDER MUST, PRIOR TO SUCH TRANSFER, FURNISH
          TO THE UNIT AGENT AND THE ISSUERS SUCH CERTIFICATIONS, LEGAL
          OPINIONS OR OTHER INFORMATION AS EITHER OF THEM MAY
          REASONABLY REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING
          MADE PURSUANT TO AN EXEMPTION FROM, OR IN A TRANSACTION NOT
          SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE SECURITIES
          ACT. AS USED HEREIN, THE TERMS "OFFSHORE TRANSACTION,"
          "UNITED STATES" AND "U.S. PERSONS"

                                      A-1
<PAGE>

          HAVE THE MEANINGS GIVEN TO THEM BY REGULATION S UNDER THE
          SECURITIES ACT."

          "EACH UNIT REPRESENTED BY THIS SECURITY CONSISTS OF ONE
          SHARE OF 14 1/2% SENIOR REDEEMABLE PREFERRED STOCK OF TNP
          ENTERPRISES, INC. (THE "COMPANY"), $1,000 LIQUIDATION
          PREFERENCE PER SHARE (A "SHARE"), AND ONE WARRANT (A
          "WARRANT") ENTITLING THE HOLDER THEREOF TO PURCHASE (AT AN
          EXERCISE PRICE OF $.01 PER LIMITED PARTNERSHIP INTEREST) A
          LIMITED PARTNERSHIP INTEREST (A "LIMITED PARTNERSHIP
          INTEREST") IN SW ACQUISITION, L.P. (THE "PARTNERSHIP")
          ENTITLING ITS HOLDER TO RECEIVE THE AMOUNT A LIMITED PARTNER
          WHO HAD MADE A $37.5388601 CAPITAL CONTRIBUTION (OR
          0.000035% OF TOTAL CAPITAL CONTRIBUTIONS AS OF THE ORIGINAL
          ISSUANCE DATE OF THE WARRANTS) WOULD RECEIVE OF THE RESIDUAL
          DISTRIBUTIONS MADE TO ALL PARTNERS IN ACCORDANCE WITH THEIR
          CAPITAL CONTRIBUTIONS AFTER A RETURN ON CAPITAL AND
          PREFERRED DISTRIBUTIONS ARE MADE TO THE LIMITED PARTNERS
          (OTHER THAN HOLDERS OF LIMITED PARTNERSHIP INTERESTS ISSUED
          UPON EXERCISE OF THE WARRANTS) AND THE GENERAL PARTNER,
          SUBJECT TO ADJUSTMENT. THE LIMITED PARTNERSHIP INTERESTS
          ISSUABLE UPON EXERCISE OF THE WARRANTS WILL PROVIDE THE
          HOLDERS WITH THE SAME RIGHTS AND OBLIGATIONS AS ARE PROVIDED
          TO LIMITED PARTNERS, EXCEPT IN CERTAIN CASES WHERE RIGHTS
          AND OBLIGATIONS APPLY ONLY TO THE ORIGINAL LIMITED PARTNERS
          AND EXCEPT FOR THE RIGHT TO RECEIVE THE PREFERRED
          DISTRIBUTIONS AND THE BENEFITS AND OBLIGATIONS UNDER CERTAIN
          TAG-ALONG AND RIGHT OF FIRST OFFER PROVISIONS. THE SHARES
          AND WARRANTS WILL BE TRANSFERABLE BY A HOLDER THEREOF
          SEPARATELY FROM EACH OTHER UPON THE EARLIEST OF: (I) 180
          DAYS AFTER THE ORIGINAL ISSUANCE DATE OF THE UNITS; (II) THE
          OCCURRENCE OF A CHANGE OF CONTROL (AS DEFINED IN THE
          STATEMENT OF RESOLUTION); (III) THE OCCURRENCE OF A VOTING
          RIGHTS TRIGGERING EVENT (AS SUCH TERM IS DEFINED IN THE
          STATEMENT OF RESOLUTION); (IV) THE EFFECTIVENESS OF
          REGISTRATION STATEMENT WITH RESPECT TO THE SENIOR PREFERRED
          STOCK; AND (V) SUCH EARLIER DATE AS DETERMINED BY CIBC WORLD
          MARKETS CORP. IN ITS SOLE DISCRETION."

          ["UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR
          SECURITIES IN DEFINITIVE FORM, THIS SECURITY MAY NOT BE
          TRANSFERRED EXCEPT AS A WHOLE BY THE DEPOSITORY TO A NOMINEE
          OF THE DEPOSITORY, OR BY ANY SUCH NOMINEE OF THE DEPOSITORY,
          OR BY THE DEPOSITORY OR NOMINEE OF SUCH SUCCESSOR DEPOSITORY
          OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITORY OR A

                                      A-2
<PAGE>

          NOMINEE OF SUCH SUCCESSOR DEPOSITORY. UNLESS THIS
          CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF
          THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION
          ("DTC"), TO THE ISSUERS OR THEIR AGENT FOR REGISTRATION OF
          TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS
          REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS
          IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY
          PAYMENT HEREON IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY
          AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY
          TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE
          BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED
          OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

          TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO
          TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF CEDE &
          CO. OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR'S
          NOMINEE."]/1/



_________________________
/1/  This paragraph is to be included only if the Unit is in global form.

                                      A-3
<PAGE>

                             TNP ENTERPRISES, INC.
                             SW ACQUISITION, L.P.

                        [        ] Units Consisting of

        [        ] Shares of 14 1/2% Senior Redeemable Preferred Stock,
                   $1,000 Liquidation Preference per Share,
                           of TNP Enterprises, Inc.
                                      and
         [        ] Warrants to Purchase Limited Partnership Interests
                            in SW Acquisition, L.P.

No.                                           CUSIP No.

          TNP ENTERPRISES, INC., a Texas corporation (the "Company"), and SW
ACQUISITON, L.P., a Texas limited partnership (the "Partnership" and, together
with the Company, the "Issuers"), hereby certify that [                    ] is
the owner of [        ] Units as described above, transferable only on the books
of the Issuers by the holder thereof in person or by his or her duly authorized
attorney, on surrender of the Certificate properly endorsed.

          Each Unit consists of one share of 14 1/2% Senior Redeemable Preferred
Stock of the Company, $1,000 liquidation preference per share (a "Share"), and
one warrant (a "Warrant") entitling the holder thereof to purchase (at an
exercise price of $.01 per limited partnership interest) a limited partnership
interest (a "Limited Partnership Interest") in the Partnership entitling its
holder to receive the amount a limited partner who had made a $37.5388601
capital contribution (or 0.000035% of total capital contributions as of the
original issuance date of the Warrants) would receive of the residual
distributions made to all partners in accordance with their capital
contributions after a return on capital and preferred distributions are made to
the limited partners (other than holders of Limited Partnership Interests issued
upon exercise of the Warrants) and the general partner, subject to adjustment.
The Limited Partnership Interests issuable upon exercise of the Warrants will
provide the holders with the same rights and obligations as are provided to
limited partners, except in certain cases where rights and obligations apply
only to the original limited partners and except for the right to receive the
preferred distributions and the benefits and obligations under certain tag-along
and right of first offer provisions.  This Unit is issued pursuant to the Unit
Agreement (the "Unit Agreement") dated as of May 26, 2000 among the Company, the
Partnership and The Bank of New York, as unit agent (the "Unit Agent"), and is
subject to the terms and provisions contained therein, all of which terms and
provisions the holder of this Unit Certificate consents by acceptance hereof.
The terms of the Shares are governed by a Statement of Resolution (the
"Statement of Resolu-

                                      A-4
<PAGE>

tion") filed with the Secretary of State of the State of Texas on May 25, 2000,
under which The Bank of New York has been named as transfer agent for the Shares
(the "Transfer Agent"), and are subject to the terms and provisions contained
therein, all of which terms and provisions the holder of this Unit Certificate
consents by acceptance hereof.

          The terms of the Warrants are governed by the warrant agreement (the
"Warrant Agreement") dated as of May 26, 2000 between the Partnership and The
Bank of New York, as warrant agent (the "Warrant Agent"), and are subject to the
terms and provisions contained therein, all of which terms and provisions the
holder of this Unit Certificate consents by acceptance hereof.

          Reference is made to the further provisions in each of the Unit
Agreement, the Statement of Resolution, the Warrant Agreement and this Unit
Certificate, which will for all purposes have the same effect as if set forth at
this place.  Copies of the Unit Agreement, the Statement of Resolution and the
Warrant Agreement are on file at the office of The Bank of New York, 101 Barclay
Street, Floor 21 West, New York, New York 10286, Attention:  Corporate Trust
Trustee Administration, and are available to any holder on written request and
without cost.

          The Shares and the Warrants represented by this Unit Certificate shall
be non-detachable and not separately transferable until the earliest of:  (i)
180 days after the original issuance date of the Units; (ii) the occurrence of a
Change of Control (as defined in the Statement of Resolution); (iii) the
occurrence of a Voting Rights Triggering Event (as such term is defined in the
Statement of Resolution); (iv) the effectiveness of a registration statement
with respect to the Shares; and (v) such earlier date as determined by CIBC
World Markets Corp. in its sole discretion.

                                      A-5
<PAGE>

          IN WITNESS WHEREOF, each of the Issuers has caused this Unit
Certificate to be signed manually by its Executing Officer.


                              TNP ENTERPRISES, INC.


                              By: __________________________
                                  Name:
                                  Title:

Dated:

                                      A-6
<PAGE>

                              SW ACQUISITION, L.P.

                              By:  SW I ACQUISITION GP, L.P.,
                                      a Texas limited partnership
                                      and its general partner

                              By:  SW II ACQUISITION LLC, a Texas
                                      limited liability company and
                                      its general partner


                              By: ___________________________________
                                  Name:  William J. Catacosinos
                                  Title:  Manager

Dated:

                                      A-7
<PAGE>

Certificate of Authentication

          This is one of the Unit Certificates referred to in the within
mentioned Unit Agreement.

THE BANK OF NEW YORK, as Unit Agent


By:________________________________
   Authorized Signatory

Date of Authentication:

                                      A-8
<PAGE>

SCHEDULE PF EXCHANGE OF CERTIFICATED UNITS/1/
------------------------------------------

The following exchanges of a part of this Global Unit for certificated Units
have been made:

<TABLE>
<CAPTION>
                                                  Number of
            Amount of          Amount of          Units of this
            decrease in        increase in        Global Unit         Signature of
            Number of          Number of          following           authorized
Date of     Units of this      Units of this      such decrease       signatory of
Exchange    Global Unit        Global Unit        (or increase)       Unit Agent
------------------------------------------------------------------------------------
<S>         <C>                <C>                <C>                 <C>
</TABLE>


________________________________
/1/  This is to be included only if the Unit is in global form.
<PAGE>

                                                                       EXHIBIT B
                                                                       ---------
                   CERTIFICATE TO BE DELIVERED UPON EXCHANGE
                     OR REGISTRATION OF TRANSFER OF UNITS

Re:  Units (the "Units") each consisting of one share of 14 1/2% Senior
     Redeemable Preferred Stock of TNP Enterprises, Inc., $1,000 liquidation
     preference per share (a "Share"), and one warrant to purchase a limited
     partnership interest in SW Acquisition, L.P. (a "Limited Partnership
     Interest")

          This Certificate relates to ___ Units held in ___* book-entry or ___*
certificated form by ________________ (the "Transferor").

The Transferor:*

          has requested the Unit Agent by written order to deliver in exchange
for its beneficial interest in the Global Unit held by the Depositary a Unit or
Units in definitive, registered form equal to its beneficial interest in such
Global Unit (or the portion thereof indicated above); or

          has requested the Unit Agent by written order to exchange or register
the transfer of a Unit or Units.

          In connection with such request and in respect of each such Unit, the
Transferor does hereby certify that the Transferor is familiar with the Unit
Agreement relating to the above captioned Units, and that the transfer of this
Unit does not require registration under the Securities Act of 1933, as amended
(the "Act"), because:*

          Such Unit is being acquired for the Transferor's own account, without
transfer (in satisfaction of Section 5 of the Unit Agreement).

          Such Unit is being transferred (i) to a qualified institutional buyer
(as defined in Rule 144A under the Act) in reliance on Rule 144A or (ii)
pursuant to an exemption from registration in accordance with Rule 904 under the
Act (and, in the case of clause (ii), based on an opinion of counsel if the
Issuers or the Unit Agent so request) and together with a certification in
substantially the form of Exhibit D to the Unit Agreement in accordance with
                          ---------
Regulation S under the Act.

                                      B-1
<PAGE>

          Such Unit is being transferred (i) in accordance with Rule 144 under
the Act (and based on an opinion of counsel if the Issuers or the Unit Agent so
request) or (ii) pursuant to an effective registration statement under the Act.

          Such Unit is being transferred to an institutional accredited investor
within the meaning of Rule 501(a)(1), (2), (3) or (7) under the Act pursuant to
a private placement exemption from the registration requirements of the Act
(together with a certification in substantially the form of Exhibit C to the
                                                            ---------
Unit Agreement and based on an opinion of counsel if the Issuers or the Unit
Agent so request).

          Such Unit is being transferred in reliance on another exemption from
the registration requirement of the Act (and based on an opinion of counsel if
the Issuers or the Unit Agent so request).



                                   ____________________________________
                                   [INSERT NAME OF TRANSFEROR]


                                   By: ________________________________


Date: ___________________________


*Check applicable box.


                                      B-2
<PAGE>

                                                                       EXHIBIT C
                                                                       ---------
                           Form of Certificate To Be
                         Delivered in Connection with
                   Transfers to Non-QIB Accredited Investors
                   -----------------------------------------

                                                        [             ], 20[   ]

THE BANK OF NEW YORK
101 Barclay Street, Floor 21 West
New York, New York  10286
Facsimile No.:  (212) 815-5915
Attention:  Corporate Trust Trustee Administration

Ladies and Gentlemen:

          In connection with our proposed purchase of certain units (the
"Units"), consisting of shares of 14 1/2% senior redeemable preferred stock of
TNP Enterprises, Inc. (the "Company"), $1,000 liquidation preference per share
("Shares"), and warrants ("Warrants" and, together with the Units and the
Shares, the "Securities"), each Warrant entitling the holder thereof to purchase
(at an exercise price of $.01 per limited partnership interest) a Limited
Partnership Interest (as defined in the Unit Agreement governing the Units) in
SW Acquisition, L.P. (together with the Company, the "Issuers"), we represent
that:

          1.  We have received a copy of the Offering Memorandum Supplement (the
"Offering Memorandum"), dated May 23, 2000, relating to the Securities and such
other information as we deem necessary in order to make our investment decision.
We acknowledge that we have read and agreed to the matters stated in the section
entitled "Notice to Investors" of such Offering Memorandum.

          2.  We understand that any subsequent transfer of the Securities is
subject to certain restrictions and conditions set forth in the Statement of
Resolution relating to the Shares and the Warrant Agreement relating to the
Warrants as described in the Offering Memorandum and the undersigned agrees to
be bound by, and not to resell, pledge or otherwise transfer the Securities
except in compliance with such restrictions and conditions and the Securities
Act of 1933, as amended (the "Securities Act"), and all applicable state
securities laws.

                                      C-1
<PAGE>

          3.  We understand that the offer and sale of the Securities have not
been registered under the Securities Act, and that the Securities may not be
offered or sold within the United States or to, or for the account or benefit
of, U.S. persons except as permitted in the following sentence. We agree, on our
own behalf and on behalf of any accounts for which we are acting as hereinafter
stated, that if we should sell any Securities, we will do so only (i) to the
Issuers or any subsidiary thereof, (ii) inside the United States in accordance
with Rule 144A under the Securities Act to a "qualified institutional buyer" (as
defined in Rule 144A promulgated under the Securities Act), (iii) inside the
United States to an institutional "accredited investor" (as defined below) that,
prior to such transfer, furnishes (or has furnished on its behalf by a U.S.
broker-dealer) to the Transfer Agent, Warrant Agent or Unit Agent a signed
letter containing certain representations and agreements relating to the
restrictions on transfer of the Shares (the form of which letter can be obtained
from the Transfer Agent, Warrant Agent or Unit Agent), (iv) outside the United
States in accordance with Rule 904 of Regulation S promulgated under the
Securities Act to non-U.S. persons, (v) pursuant to the exemption from
registration provided by Rule 144 under the Securities Act (if available), or
(vi) pursuant to an effective registration statement under the Securities Act,
and we further agree to provide to any person purchasing any of the Securities
from us a notice advising such purchaser that resales of the Securities are
restricted as stated herein.

          4.  We understand that, on any proposed resale of any Securities, we
will be required to furnish to the Transfer Agent, Warrant Agent or Unit Agent
and the Issuers such certification, legal opinions and other information as the
Transfer Agent, Warrant Agent or Unit Agent and the Issuers may reasonably
require to confirm that the proposed sale complies with the foregoing
restrictions. We further understand that the Securities purchased by us will
bear a legend to the foregoing effect.

          5.  We are an institutional "accredited investor" (as defined in Rule
501(a)(1), (2), (3) or (7) of Regulation D under the Securities Act) and have
such knowledge and experience in financial and business matters as to be capable
of evaluating the merits and risks of our investment in the Securities, and we
and any accounts for which we are acting are each able to bear the economic risk
of our or their investment, as the case may be.

          6.  We are acquiring the Securities purchased by us for our account or
for one or more accounts (each of which is

                                      C-2
<PAGE>

an institutional "accredited investor") as to each of which we exercise sole
investment discretion.

                                      C-3
<PAGE>

          You, the Issuers, the Transfer Agent, Warrant Agent or Unit Agent and
others are entitled to rely upon this letter and are irrevocably authorized to
produce this letter or a copy hereof to any interested party in any
administrative or legal proceeding or official inquiry with respect to the
matters covered hereby.

                                        Very truly yours,

                                        [Name of Transferee]


                                        By: _____________________________
                                            Name:
                                            Title:

                                      C-4
<PAGE>

                                                                       EXHIBIT D
                                                                       ---------
                      Form of Certificate To Be Delivered
                         in Connection with Transfers
                           Pursuant to Regulation S
                     ------------------------------------

                                                        [             ], 20[   ]

THE BANK OF NEW YORK
101 Barclay Street, Floor 21 West
New York, New York  10286
Facsimile No.:  (212) 815-5915
Attention:  Corporate Trust Trustee Administration

Ladies and Gentlemen:

          In connection with our proposed purchase of certain units (the
"Units"), consisting of shares of 14 1/2% senior redeemable preferred stock of
TNP Enterprises, Inc. (the "Company"), $1,000 liquidation preference per share
("Shares"), and warrants ("Warrants" and, together with the Units and the
Shares, the "Securities"), each Warrant entitling the holder thereof to purchase
(at an exercise price of $.01 per limited partnership interest) a Limited
Partnership Interest (as defined in the Unit Agreement governing the Units) in
SW Acquisition, L.P. (together with the Company, the "Issuers"), we represent
that:

          (1) the offer of the Securities was not made to a person in the United
     States;

          (2) either (a) at the time the buy offer was originated, the
     transferee was outside the United States or we and any person acting on our
     behalf reasonably believed that the transferee was outside the United
     States, or (b) the transaction was executed in, on or through the
     facilities of a designated off-shore securities market and neither we nor
     any person acting on our behalf knows that the transaction has been pre-
     arranged with a buyer in the United States;

          (3) no directed selling efforts have been made in the United States in
     contravention of the requirements of Rule 903(b) or Rule 904(b) of
     Regulation S, as applicable;

          (4) the transaction is not part of a plan or scheme to evade the
     registration requirements of the Securities Act; and

                                      D-1
<PAGE>

          (5) we have advised the transferee of the transfer restrictions
     applicable to the Securities.

          You, the Issuers and counsel for the Issuers are entitled to rely upon
this letter and are irrevocably authorized to produce this letter or a copy
hereof to any interested party in any administrative or legal proceedings or
official inquiry with respect to the matters covered hereby.  Terms used in this
certificate have the meanings set forth in Regulation S.

                                        Very truly yours,

                                        [Name of Transferor]


                                        By: ___________________________
                                            Name:
                                            Title:

                                      D-2