Ex 4(a) Sixth Supplemental Indenture


    
      
        

      

    

    
      EXHIBIT
        4(a)

      


      


      PUBLIC
        SERVICE COMPANY OF OKLAHOMA

       

      and

       

      THE
        BANK
        OF NEW YORK,

      AS
        TRUSTEE

       

      ___________________

      


      


      SIXTH
        SUPPLEMENTAL INDENTURE

      


      Dated
        as
        of August 10, 2006

      


      


      Supplemental
        to the Indenture

      dated
        as
        of November 1, 2000

      


      


      6.15%
        Senior Notes, Series F, due 2016


      
        
          
          

        

        
          
          

          
            

          

        

        
          
          

          
          

        

      

      


      SIXTH
        SUPPLEMENTAL INDENTURE, dated as of August 10, 2006, between PUBLIC SERVICE
        COMPANY OF OKLAHOMA, a corporation duly organized and existing under the
        laws of
        the State of Oklahoma (the “Company”), and THE BANK OF NEW YORK, a New York
        banking corporation organized and existing under the laws of the State of
        New
        York, as Trustee under the Original Indenture referred to below (the “Trustee”).


      


      RECITALS
        OF THE COMPANY

      


      The
        Company has heretofore executed and delivered to the Trustee an indenture
        dated
        as of November 1, 2000 (the “Original Indenture”), to provide for the issuance
        from time to time of its debentures, notes or other evidences of indebtedness
        (the “Senior Notes”), the form and terms of which are to be established as set
        forth in Section 201 and 301 of the Original Indenture.

      


      Section
        901 of the Original Indenture provides, among other things, that the Company
        and
        the Trustee may enter into indentures supplemental to the Original Indenture
        for, among other things, the purpose of establishing the form and terms of
        the
        Senior Notes of any series as permitted in Sections 201 and 301 of the Original
        Indenture.

      


      The
        Company desires to create a series of the Senior Notes in an aggregate principal
        amount of $150,000,000 to be designated the “6.15% Senior Notes, Series F, due
        2016” (the “6.15% Senior Notes”), and all action on the part of the Company
        necessary to authorize the issuance of the 6.15% Senior Notes under the Original
        Indenture and this Sixth Supplemental Indenture has been duly
        taken.

      


      All
        acts
        and things necessary to make the 6.15% Senior Notes, when executed by the
        Company and completed, authenticated and delivered by the Trustee as provided
        in
        the Original Indenture and this Sixth Supplemental Indenture, the valid and
        binding obligations of the Company and to constitute these presents a valid
        and
        binding supplemental indenture and agreement according to its terms, have
        been
        done and performed.

      


      NOW,
        THEREFORE, THIS SIXTH SUPPLEMENTAL INDENTURE WITNESSETH:

      


      That
        in
        consideration of the premises and of the acceptance and purchase of the 6.15%
        Senior Notes by the Holders thereof and of the acceptance of this trust by
        the
        Trustee, the Company covenants and agrees with the Trustee, for the equal
        benefit of the Holders of the 6.15% Senior Notes, as follows: 

      


      ARTICLE
        ONE

      Definitions

      


      The
        use
        of the terms and expressions herein is in accordance with the definitions,
        uses
        and constructions contained in the Original Indenture and the form of the
        Global
        Security attached hereto as Exhibit
        A.

       

      ARTICLE
        TWO

      Terms
        and
        Issuance of the 6.15% Senior Notes

      


      SECTION
        201. Issue
        of 6.15% Senior Notes

      


      A
        series
        of Senior Notes which shall be designated the “6.15% Senior Notes, Series F, due
        2016” shall be executed, authenticated and delivered from time to time in
        accordance with the provisions of, and shall in all respects be subject to,
        the
        terms, conditions and covenants of, the Original Indenture and this Sixth
        Supplemental Indenture (including the form of Global Security set forth in
        Exhibit
        A
        hereto).
        The aggregate principal amount of the 6.15% Senior Notes, which may be
        authenticated and delivered under this Sixth Supplemental Indenture shall
        initially be $150,000,000, and such principal amount of the 6.15% Senior
        Notes
        may be increased from time to time. All 6.15% Senior Notes need not be issued
        at
        the same time and such series may be reopened at any time, without the consent
        of any Holder, for issuance of additional 6.15% Senior Notes. Any such
        additional 6.15% Senior Notes will have the same interest rate, maturity
        and
        other terms as those initially issued.

      


      SECTION
        202. Form
        of 6.15% Senior Notes, Incorporation of Terms

      


      The
        6.15%
        Senior Notes shall be substantially in the form of the Global Security attached
        hereto as Exhibit
        A.
        The
        terms of such 6.15% Senior Notes are herein incorporated by reference and
        are
        part of this Sixth Supplemental Indenture.

      


      SECTION
        203. Depositary
        for Global Securities

      


      The
        Depositary for any Global Securities of the series of which this 6.15% Senior
        Note is a part shall be The Depository Trust Company in The City of New
        York.

      


      SECTION
        204. Restrictions
        on Liens

      


      The
        covenant contained in Section 1007 of the Original Indenture shall not be
        applicable to the 6.15% Senior Notes.

      


      So
        long
        as any of the 6.15% Senior Notes are outstanding, the Company will not create
        or
        suffer to be created or to exist any additional mortgage, pledge, security
        interest, or other lien (collectively “Liens”) on any of its utility properties
        or tangible assets now owned or hereafter acquired to secure any indebtedness
        for borrowed money (“Secured Debt”), without providing that the 6.15% Senior
        Notes will be similarly secured. This restriction does not apply to the
        Company’s subsidiaries, nor will it prevent any of them from creating or
        permitting to exist Liens on their property or assets to secure any Secured
        Debt. Further, this restriction on Secured Debt does not apply to the Company’s
        existing first mortgage bonds that have previously been issued under its
        Mortgage and Deed of Trust, dated July 1, 1945, between the Company and Liberty
        Bank and Trust Company of Tulsa, National Association, as successor to The
        First
        National Bank and Trust Company of Tulsa, now The Bank of New York, as successor
        Trustee or any indenture supplemental thereto; provided that this restriction
        will apply to future issuances thereunder (other than issuances of refunding
        first mortgage bonds). In addition, this restriction does not prevent the
        creation or existence of:

      


      (a) Liens
        on
        property existing at the time of acquisition or construction of such property
        (or created within one year after completion of such acquisition or
        construction), whether by purchase, merger, construction or otherwise, or
        to
        secure the payment of all or any part of the purchase price or construction
        cost
        thereof, including the extension of any Liens to repairs, renewals,
        replacements, substitutions, betterments, additions, extensions and improvements
        then or thereafter made on the property subject thereto; 

      


      (b) Financing
        of the Company’s accounts receivable for electric service; 

      


      (c) Any
        extensions, renewals or replacements (or successive extensions, renewals
        or
        replacements), in whole or in part, of liens permitted by the foregoing clauses;
        and

      


      (d) The
        pledge of any bonds or other securities at any time issued under any of the
        Secured Debt permitted by the above clauses.

      


      In
        addition to the permitted issuances above, Secured Debt not otherwise so
        permitted may be issued in an amount that does not exceed 15% of Net Tangible
        Assets as defined below. 

      


      “Net
        Tangible Assets” means the total of all assets (including revaluations thereof
        as a result of commercial appraisals, price level restatement or otherwise)
        appearing on the Company’s balance sheet, net of applicable reserves and
        deductions, but excluding goodwill, trade names, trademarks, patents,
        unamortized debt discount and all other like intangible assets (which term
        shall
        not be construed to include such revaluations), less the aggregate of the
        Company’s current liabilities appearing on such balance sheet. For purposes of
        this definition, the Company’s balance sheet does not include assets and
        liabilities of its subsidiaries.

      


      This
        restriction also does not apply to or prevent the creation or existence of
        leases made, or existing on property acquired, in the ordinary course of
        business.

      


      SECTION
        205. Place
        of Payment

      


      The
        Place
        of Payment in respect of the 6.15% Senior Notes will be at the principal
        office
        or place of business of the Trustee or its successor in trust under the
        Indenture, which, at the date hereof, is located at 101 Barclay Street, New
        York, NY 10281, Attention: Corporate Trust Department.

      


      SECTION
        206. Sinking
        Funds.

      


      Article
        Twelve of the Indenture shall not apply to the 6.15% Senior
        Notes.


      SECTION
        207. Redemption

      


      The
        6.15%
        Senior Notes shall be redeemable at the option of the Company, in whole at
        any
        time or in part from time to time, upon not less than thirty but not more
        than
        sixty days’ previous notice given by mail to the registered owners of the 6.15%
        Senior Notes at a redemption price equal to the greater of (i) 100% of the
        principal amount of the 6.15% Senior Notes being redeemed and (ii) the sum
        of
        the present values of the remaining scheduled payments of principal and interest
        on the 6.15% Senior Notes being redeemed (excluding the portion of any such
        interest accrued to the date of redemption) discounted (for purposes of
        determining present value) to the redemption date on a semi-annual basis
        (assuming a 360-day year consisting of twelve 30-day months) at the Treasury
        Rate (as defined below) plus 20 basis points, plus, in each case, accrued
        interest thereon to the date of redemption.

      


      “Comparable
        Treasury Issue” means the United States Treasury security selected by an
        Independent Investment Banker as having a maturity comparable to the remaining
        term of the 6.15%
        Senior Notes
        that would be utilized, at the time of selection and in accordance with
        customary financial practice, in pricing new issues of corporate debt securities
        of comparable maturity to the remaining term of the 6.15% Senior
        Notes.

      


      “Comparable
        Treasury Price” means, with respect to any redemption date, (1) the average of
        the Reference Treasury Dealer Quotations for such redemption date after
        excluding the highest and lowest such Reference Treasury Dealer Quotations,
        or
        (2) if fewer than four such Reference Treasury Dealer Quotations are obtained,
        the average of all such quotations.

      


      “Independent
        Investment Banker” means one of the Reference Treasury Dealers appointed by the
        Company and reasonably acceptable to the Trustee.

      


      “Reference
        Treasury Dealer” means a primary U.S. government securities dealer in New York
        City selected by the Company and reasonably acceptable to the
        Trustee.

      


      “Reference
        Treasury Dealer Quotation” means, with respect to each Reference Treasury Dealer
        and any redemption date, the average, as determined by the Trustee, of the
        bid
        and asked prices for the Comparable Treasury Issue (expressed in each case
        as a
        percentage of its principal amount) quoted in writing to the Trustee by such
        Reference Treasury Dealer at or before 5:00 p.m., New York City time, on
        the
        third Business Day preceding such redemption date.

      


      “Treasury
        Rate” means, with respect to any redemption date, the rate per annum equal to
        the semi-annual equivalent yield to maturity of the Comparable Treasury Issue,
        assuming a price for the Comparable Treasury Issue (expressed as a percentage
        of
        its principal amount) equal to the Comparable Treasury Price for such redemption
        date.

       

      ARTICLE
        THREE

       

      Miscellaneous

      


      SECTION
        301. Execution
        as Supplemental Indenture

      


      This
        Sixth Supplemental Indenture is executed and shall be construed as an indenture
        supplemental to the Original Indenture and, as provided in the Original
        Indenture, this Sixth Supplemental Indenture forms a part thereof.

      


      SECTION
        302. Conflict
        with Trust Indenture Act

      


      If
        any
        provision hereof limits, qualifies or conflicts with another provision hereof
        which is required to be included in this Sixth Supplemental Indenture by
        any of
        the provisions of the Trust Indenture Act, such required provision shall
        control. 

      


      SECTION
        303. Effect
        of Headings

      


      The
        Article and Section headings herein are for convenience only and shall not
        affect the construction hereof.

      


      SECTION
        304. Successors
        and Assigns

      


      All
        covenants and agreements by the Company in this Sixth Supplemental Indenture
        shall bind its successors and assigns, whether so expressed or not.

      


      SECTION
        305. Separability
        Clause

      


      In
        case
        any provision in this Sixth Supplemental Indenture or in the 6.15% Senior
        Notes
        shall be invalid, illegal or unenforceable, the validity, legality and
        enforceability of the remaining provisions shall not in any way be affected
        or
        impaired thereby.

      


      SECTION
        306. Benefits
        of Sixth Supplemental Indenture

      


      Nothing
        in this Sixth Supplemental Indenture or in the 6.15% Senior Notes, express
        or
        implied, shall give to any Person, other than the parties hereto and their
        successors hereunder and the Holders, any benefit or any legal or equitable
        right, remedy or claim under this Sixth Supplemental Indenture.

      


      SECTION
        307. Execution
        and Counterparts

      


      This
        Sixth Supplemental Indenture may be executed in any number of counterparts,
        each
        of which shall be deemed to be an original, but all such counterparts shall
        together constitute but one and the same instrument.


      IN
        WITNESS WHEREOF, the parties hereto have caused this Sixth Supplemental
        Indenture to be duly executed and attested, all as of the day and year first
        above written. 

      


      
        	 	
                PUBLIC
                  SERVICE COMPANY OF OKLAHOMA

              
	 	 	 
	 	
                By:

              	
                /s/
                  Stephan T. Haynes

              
	 	 	
                Assistant
                  Treasurer

              
	
                Attest:

              	 	 
	 	 	 
	
                /s/
                  Jeffrey D. Cross

              	 	 
	
                Assistant
                  Secretary

              	 	 
	 	 	 
	 	
                THE
                  BANK OF NEW YORK, as Trustee

              
	 	 	 
	 	
                By:

              	
                /s/
                  Beata Hryniewicka

              
	 	 	
                Authorized
                  Signatory

              
	
                Attest:

              	 	 
	 	 	 
	
                /s/
                  Van Brown

              	 	 
	
                Name: Van
                  Brown

              	 	 
	
                Title: Vice
                  President

              	 	 


      

       

      

      STATE
        OF
        OHIO  )

      :
        ss.:

      COUNTY
        OF
        FRANKLIN )

       

          On
        the 10th
        day of August, 2006, personally appeared before me, a Notary Public within
        and
        for said County in the State of Ohio, Stephan T. Haynes and Jeffrey D. Cross,
        to
        me known and known to me to be respectively an Assistant Treasurer and an
        Assistant Secretary of Public Service Company of Oklahoma, one of the
        corporations named in and which executed the foregoing instrument, who severally
        acknowledged that they did sign said instrument as such Assistant Treasurer
        and
        Assistant Secretary for and on behalf of said corporation and that the same
        is
        their free act and deed as such Assistant Treasurer and Assistant Secretary,
        respectively, and the free and corporate act and deed of said corporation.
        

      


      In
        witness whereof, I have hereunto set my hand notarial seal this 10th day
        of
        August, 2006.

      


      
        	 	
                /s/
                  Leslye R. Creek

              
	 	
                Notary
                  Public, State of Ohio

              
	 	
                Commission
                  Expires 03-17-09

              


      

       

      STATE
        OF
        NEW YORK )

      :
        ss.:

      COUNTY
        OF
        NEW YORK )

      


      On
        the
        10th day of August, 2006, personally appeared before me, a Notary Public
        within
        and for said County in the State of New York, Beata Hryniewicka and Van Brown,
        to me known and known to me to be respectively the Assistant Vice President
        and
        Vice President of The Bank of New York, one of the corporations named in
        and
        which executed the foregoing instrument, who severally acknowledged that
        they
        did sign said instrument as such Assistant Vice President and Vice President
        for
        and on behalf of said corporation and that the same is their free act and
        deed
        as such Assistant Vice President and Vice President, respectively, and the
        free
        and corporate act and deed of said corporation. 

      


      In
        witness whereof, I have hereunto set my hand notarial seal this 10th day
        of
        August, 2006.

       

      
        	 	
                /s/
                  Carlos R. Lociano

              
	 	
                Notary
                  Public, State of New York

              
	 	
                Commission
                  Expires 04-30-10

              


      

      
        

      

    

     

    
      Exhibit
        A

      


      THIS
        SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER
        REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITARY OR A NOMINEE OF
        A
        DEPOSITARY. THIS SECURITY IS EXCHANGEABLE FOR SECURITIES REGISTERED IN THE
        NAME
        OF A PERSON OTHER THAN THE DEPOSITARY OR ITS NOMINEE ONLY IN THE LIMITED
        CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND NO TRANSFER OF THIS SECURITY
        (OTHER THAN A TRANSFER OF THIS SECURITY AS A WHOLE 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) MAY BE REGISTERED EXCEPT IN LIMITED
        CIRCUMSTANCES. 

      


      Unless
        this certificate is presented by an authorized representative of The Depository
        Trust Company, a New York corporation (“DTC”), to Public Service Company of
        Oklahoma or its agent for registration of transfer, exchange or payment,
        and any
        definitive certificate issued is registered in the name of Cede & Co. or in
        such other name as is requested by an authorized representative of DTC (and
        any
        payment 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 in as much as the registered
        owner hereof, Cede & Co., has an interest herein.

      


      No.
        R-1

      


      PUBLIC
        SERVICE COMPANY OF OKLAHOMA

      6.15%
        Senior Notes, Series F, due 2016

      


      CUSIP
        No.
744533
        BH
        2        
        $150,000,000

      


      PUBLIC
        SERVICE COMPANY OF OKLAHOMA, a corporation duly organized and existing under
        the
        laws of the State of Oklahoma (the “Company”, which term includes any successor
        Person under the Indenture hereinafter referred to), for value received,
        hereby
        promises to pay to CEDE & CO. or registered assigns, the principal sum of
ONE
        HUNDRED FIFTY MILLION DOLLARS
        ($150,000,000) on August 1, 2016 (the “Final Maturity”), and to pay interest
        thereon from August 10, 2006 or from the most recent Interest Payment Date
        to
        which interest has been paid or duly provided for, semi-annually on February
        1
        and August 1 each year, commencing February 1, 2007, at the interest rate
        per
        annum specified above, until the principal amount shall have been paid or
        duly
        provided for. Interest shall be computed on the basis of a 360-day year of
        twelve 30-day months.

      


      The
        interest so payable, and punctually paid or duly provided for, on any Interest
        Payment Date will, as provided in such Indenture, be paid to the Person in
        whose
        name this Security (or one or more Predecessor Securities) is registered
        at the
        close of business on the Regular Record Date for such interest, which shall
        be
        the January 15 or July 15 (whether or not a Business Day) immediately preceding
        the Interest Payment Date. Any such interest not so punctually paid or duly
        provided for will forthwith cease to be payable to the Holder on such Regular
        Record Date and may either be paid to the Person in whose name this Security
        (or
        one or more Predecessor Securities) is registered at the close of business
        on a
        Special Record Date for the payment of such Defaulted Interest to be fixed
        by
        the Trustee, notice whereof shall be given to Holders of Securities of this
        series not less than 10 days prior to such Special Record Date, or be paid
        at
        any time in any other lawful manner not inconsistent with the requirements
        of
        any securities exchange on which the Securities of this series may be listed,
        and upon such notice as may be required by such exchange, all as more fully
        provided in said Indenture.

      


      Payment
        of the principal of (and premium, if any) and interest on this Security will
        be
        made at the office or agency of the Company maintained for that purpose in
        the
        Borough of Manhattan, The City of New York, New York, in such coin or currency
        of the United States of America as at the time of payment is legal tender
        for
        the payment of public and private debts; provided, however, that at the option
        of the Company payment of interest may be made by check mailed to the address
        of
        the Person entitled thereto as such address shall appear in the Security
        Register.

      


      This
        Security has initially been issued in the form of a Global Security, and
        the
        Company has initially designated The Depository Trust Company (the “Depositary”,
        which term shall include any successor depositary) as the depositary for
        this
        Security. For as long as this Security or any portion hereof is issued in
        such
        form, and notwithstanding the previous paragraph, all payments of interest,
        principal and other amounts in respect of this Security or portion thereof
        shall
        be made to the Depositary or its nominee in accordance with the Applicable
        Procedures in the coin or currency specified above and as further provided
        herein.

      


      This
        Security is one of a duly authorized issue of securities of the Company (the
        “Securities”), issued and to be issued in one or more series under an Indenture,
        dated as of November 1, 2000, as amended and supplemented from time to time
        (the
“Indenture”, which term shall have the meaning assigned to it in such
        instrument), between the Company and The Bank of New York, a New York banking
        corporation, as Trustee (the “Trustee”, which term includes any successor
        trustee under the Indenture), as to which Indenture and all indentures
        supplemental thereto reference is hereby made for a statement of the respective
        rights, limitations of rights, duties and immunities thereunder of the Company,
        the Trustee and the Holders and of the terms upon which the Securities are,
        and
        are to be, authenticated and delivered. This Security is one of the series
        designated on the face hereof, limited in aggregate principal amount to
        $150,000,000; provided, however, the aggregate principal amount hereof can
        be
        increased, without the consent of the Holder, as permitted by the provisions
        of
        the Original Indenture. The provisions of this Security, together with the
        provisions of the Indenture, shall govern the rights, obligations, duties
        and
        immunities of the Holder, the Company and the Trustee with respect to this
        Security, provided that, if any provision of this Security necessarily conflicts
        with any provision of the Indenture, the provision of this Security shall
        be
        controlling to the fullest extent permitted under the Indenture.

      


      The
        Securities of this Series are subject to redemption upon not less than 30
        nor
        more than 60 days’ notice by mail to the Holders of such Securities at their
        addresses in the Security Register for such Series at the option of the Company,
        in whole or in part, from time to time at a Redemption Price equal to
the
        greater of (i) 100% of the principal amount of the Securities being redeemed
        and
        (ii) the sum of the present values of the remaining scheduled payments of
        principal and interest on the Securities being redeemed (excluding the portion
        of any such interest accrued to the date of redemption) discounted (for purposes
        of determining present value) to the redemption date on a semi-annual basis
        (assuming a 360-day year consisting of twelve 30-day months) at the Treasury
        Rate (as defined below) plus 20 basis points, plus, in each case, accrued
        interest thereon to the date of redemption.

      


      “Comparable
        Treasury Issue” means the United States Treasury security selected by an
        Independent Investment Banker as having a maturity comparable to the remaining
        term of the Securities that would be utilized, at the time of selection and
        in
        accordance with customary financial practice, in pricing new issues of corporate
        debt securities of comparable maturity to the remaining term of the
        Securities.

      


      “Comparable
        Treasury Price” means, with respect to any redemption date, (1) the average of
        the Reference Treasury Dealer Quotations for such redemption date after
        excluding the highest and lowest such Reference Treasury Dealer Quotations,
        or
        (2) if fewer than four such Reference Treasury Dealer Quotations are obtained,
        the average of all such quotations.

      


      “Independent
        Investment Banker” means one of the Reference Treasury Dealers appointed by the
        Company and reasonably acceptable to the Trustee.

      


      “Reference
        Treasury Dealer” means a primary U. S. government securities dealer in New York
        City selected by the Company and reasonably acceptable to the
        Trustee.

      


      “Reference
        Treasury Dealer Quotations” mean, with respect to each Reference Treasury Dealer
        and any redemption date, the average, as determined by the Trustee, of the
        bid
        and asked prices for the Comparable Treasury Issue (expressed in each case
        as a
        percentage of its principal amount) quoted in writing to the Trustee by such
        Reference Treasury Dealer at or before 5:00 p.m., New York City time, on
        the
        third Business Day preceding such redemption date.

      


      “Treasury
        Rate” means, with respect to any redemption date, the rate per annum equal to
        the semi-annual equivalent yield to maturity of the Comparable Treasury Issue,
        assuming a price for the Comparable Treasury Issue (expressed as a percentage
        of
        its principal amount) equal to the Comparable Treasury Price for such redemption
        date.

      


      If
        notice
        has been given as provided in the Indenture and funds for redemption of any
        Securities (or any portion thereof) called for redemption shall have been
        made
        available on the Redemption Date referred to in such notice, such Securities
        (or
        any portion thereof) will cease to bear interest on the date fixed for such
        redemption specified in such notice and the only right of the Holders of
        such
        Securities will be to receive payment of the Redemption Price.

      


      In
        the
        event of redemption of this Security in part only, a new Security or Securities
        of this Series and of like tenor for the unredeemed portion hereof will be
        issued in the name of the Holder hereof upon the cancellation
        hereof.

      


      The
        Securities of this series will not be subject to any sinking fund.

      


      If
        an
        Event of Default with respect to Securities of this series shall occur and
        be
        continuing, the principal of the Securities of this series may be declared
        due
        and payable in the manner and with the effect provided in the
        Indenture.

      


      Interest
        payments with respect to this Security will be computed and paid on the basis
        of
        a 360-day year of twelve 30-day months for the actual number of days
        elapsed.

      


      The
        Indenture permits, with certain exceptions as therein provided, the amendment
        thereof and the modification of the rights and obligations of the Company
        and
        the rights of the Holders of the Securities of each series to be affected
        under
        the Indenture at any time by the Company and the Trustee with the consent
        of the
        Holders of a majority in principal amount of the Securities at the time
        Outstanding of all series to be affected (voting as a class). The Indenture
        also
        contains provisions permitting the Holders of specified percentages in principal
        amount of the Securities of each Series at the time Outstanding, on behalf
        of
        the Holders of all Securities of such series, to waive compliance by the
        Company
        with certain provisions of the Indenture and certain past defaults under
        the
        Indenture and their consequences. Any such consent or waiver by the Holder
        of
        this Security shall be conclusive and binding upon such Holder and upon all
        future Holders of this Security and of any Security issued upon the registration
        of transfer hereof or in exchange herefor or in lieu hereof, whether or not
        notation of such consent or waiver is made upon this Security.

      


      No
        reference herein to the Indenture and no provision of this Security or of
        the
        Indenture shall alter or impair the obligation of the Company, which is absolute
        and unconditional, to pay the principal of, premium, if any, and interest
        on
        this Security at the times, place and rate, and in the coin or currency,
        herein
        prescribed.

      


      This
        Security shall be exchangeable for Securities registered in the names of
        Persons
        other than the Depositary with respect to such series or its nominee only
        as
        provided in the Indenture. This Security shall be so exchangeable if (x)
        the
        Depositary notifies the Company that it is unwilling or unable to continue
        as
        Depositary for such series or at any time ceases to be a clearing agency
        registered as such under the Exchange Act, (y) the Company executes and delivers
        to the Trustee an Officers’ Certificate providing that this Security shall be so
        exchangeable or (z) there shall have occurred and be continuing an Event
        of
        Default with respect to the Securities of such series. Securities so issued
        in
        exchange for this Security shall be of the same series, having the same interest
        rate, if any, and maturity and having the same terms as this Security, in
        authorized denominations and in the aggregate having the same principal amount
        as this Security and registered in such names as the Depositary for such
        Global
        Security shall direct.

      


      As
        provided in the Indenture and subject to certain limitations therein set
        forth,
        the transfer of a Security of the series of which this Security is a part
        is
        registrable in the Security Register, upon surrender of this Security for
        registration of transfer at the office or agency of the Company in any place
        where the principal of and any premium and interest on this Security are
        payable, duly endorsed by, or accompanied by a written instrument of transfer
        in
        form satisfactory to the Company and the Security Registrar duly executed
        by,
        the Holder hereof or his attorney duly authorized in writing, and thereupon
        one
        or more new Securities of this Series and of like tenor, of authorized
        denominations and for the same aggregate principal amount, will be issued
        to the
        designated transferee or transferees.

      


      The
        Securities of this Series are issuable only in registered form without coupons
        in denominations of $1,000 and any integral multiple thereof. As provided
        in the
        Indenture and subject to certain limitations therein set forth, Securities
        of
        this Series are exchangeable for a like aggregate principal amount of Securities
        of this Series and of like tenor of a different authorized denomination,
        as
        requested by the Holder surrendering the same.

      


      No
        service charge shall be made for any such registration of transfer or exchange,
        but the Company may require payment of a sum sufficient to cover any tax
        or
        other governmental charge payable in connection therewith.

      


      Prior
        to
        due presentment of this Security for registration of transfer, the Company,
        the
        Trustee and any agent of the Company or the Trustee may treat the Person
        in
        whose name this Security is registered as the owner hereof for all purposes,
        whether or not this Security be overdue, and neither the Company, the Trustee
        nor any such agent shall be affected by notice to the contrary.

      


      For
        so
        long as this Security is issued in the form of a Global Security, any notice
        to
        be given to the Holder of this Security shall be deemed to have been duly
        given
        to such Holder when given to the Depositary, or its nominee, in accordance
        with
        its Applicable Procedures. Neither the Company nor the Trustee will have
        any
        responsibility with respect to those policies and procedures or for any notices
        or other communications among the Depositary, its direct and indirect
        participants and the beneficial owners of this Security in global
        form.

      


      If
        at any
        time this Security is not represented by a Global Security, any notice to
        be
        given to the Holder of this Security shall be deemed to have been duly given
        to
        such Holder upon the mailing of such notice to the Holder at such Holder’s
        address as it appears on the Security Register maintained by the Company
        or its
        agent as of the close of business preceding the day such notice is
        given.

      


      Neither
        the failure to give any notice nor any defect in any notice given to the
        Holder
        of this Security or any other Security of this series will affect the
        sufficiency of any notice given to another Holder of any Securities of this
        series.

       

      The
        Indenture provides that the Company, at its option, (a) will be discharged
        from
        any and all obligations in respect of the Securities (except for certain
        obligations to register the transfer or exchange of Securities, replace stolen,
        lost or mutilated Securities, maintain paying agencies and hold moneys for
        payment in trust) or (b) need not comply with certain restrictive covenants
        of
        the Indenture, in each case if the Company deposits, in trust, with the Trustee
        money or U.S. Government Obligations which, through the payment of interest
        thereon and principal thereof in accordance with their terms, will provide
        money, in an amount sufficient to pay all the principal of, and premium,
        if any,
        and interest, if any, on the Securities on the dates such payments are due
        in
        accordance with the terms of such Securities, and certain other conditions
        are
        satisfied.

      


      No
        recourse shall be had for the payment of the principal of or the interest
        on
        this Security, or for any claim based hereon, or otherwise in respect hereof,
        or
        based on or in respect of the Indenture or any indenture supplemental thereto,
        against any incorporator, organizer, member, limited partner, stockholder,
        officer or director, as such, past, present or future, of the Company or
        any
        successor Person, whether by virtue of any constitution, statute or rule
        of law,
        or by the enforcement of any assessment or penalty or otherwise, all such
        liability being, by the acceptance hereof and as part of the consideration
        for
        the issuance hereof, expressly waived and released.

      


      This
        Security shall be governed by and construed in accordance with the laws of
        the
        State of New York without regard to principles of conflict of law except
        Section
        5-1401 of the New York General Obligations Law.

      


      All
        terms
        used in this Security which are defined in the Indenture shall have the meanings
        ascribed to them in the Indenture. 

      


      Unless
        the certificate of authentication hereon has been executed by the Trustee
        referred to herein by manual signature, this Security shall not be entitled
        to
        any benefit under the Indenture or be valid or obligatory for any purpose.
        

      


      IN
        WITNESS WHEREOF, Public Service Company of Oklahoma has caused this instrument
        to be duly executed.

      


      
        	 	
                PUBLIC
                  SERVICE COMPANY OF OKLAHOMA

              
	 	 	 
	 	
                By:

              	
                /s/
                  Stephan T. Haynes

              
	 	 	
                Assistant
                  Treasurer

              


      

      


      This
        is
        one of the Securities of the series designated herein and referred to in
        the
        within-mentioned Indenture.

      


      
        	
                Dated:
                  August 10, 2006

              	
                THE
                  BANK OF NEW YORK

              
	 	 	 
	 	
                By:

              	
                /s/
                  Beata Hryniewicka

              
	 	 	
                Authorized
                  Signatory

              


      

      



      
        

      


      FOR
        VALUE
        RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s)
        unto

      


      (PLEASE
        INSERT SOCIAL SECURITY OR OTHER

      IDENTIFYING
        NUMBER OF ASSIGNEE)

      


      _______________________________________

      


      ________________________________________________________________

      


      ________________________________________________________________

      (PLEASE
        PRINT OR TYPE NAME AND ADDRESS, INCLUDING ZIP CODE, OF

      ________________________________________________________________

      ASSIGNEE)
        the within Note and all rights thereunder, hereby

      ________________________________________________________________

      irrevocably
        constituting and appointing such person attorney to 

      ________________________________________________________________

      transfer
        such Note on the books of the Issuer, with full

      ________________________________________________________________

      power
        of
        substitution in the premises.

      


      Dated:________________________  _________________________

      


      NOTICE: The
        signature to this assignment must correspond with the name as written upon
        the
        face of the within Note in every particular, without alteration or enlargement
        or any change whatever and NOTICE: Signature(s) must be guaranteed by a
        financial institution that is a member of the Securities Transfer Agents
        Medallion Program (“STAMP”), the Stock Exchange Medallion Program (“SEMP”) or
        the New York Stock Exchange, Inc. Medallion Signature Program
        (“MSP”).