Document:

<PAGE>

      Portions of this Exhibit have been omitted pursuant to a request for
             confidential treatment and the non-public information
                          has been filed with the SEC.

                                                                    EXHIBIT 10.5

                     FIRST AMENDMENT TO SETTLEMENT AGREEMENT

         THIS FIRST AMENDMENT TO SETTLEMENT AGREEMENT ("First Amendment"),
effective as of October 1, 2003, is made by and among Applera Corporation, a
Delaware corporation, acting through its Applied Biosystems Group ("AB"), Irena
Bronstein, of Newton, Massachusetts ("Bronstein"), Lumigen, Inc., a Michigan
corporation ("Lumigen"), A. Paul Schaap, of Grosse Point Park, Michigan
("Schaap"), Wayne State University, a not for profit constitutional body
corporate organized under the laws of the State of Michigan ("WSU"), and
Diagnostic Products Corporation, a California corporation, ("DPC");

         WHEREAS, Bronstein, Lumigen, Schaap, and WSU, along with Tropix, Inc.,
a Delaware corporation ("Tropix"), entered into a Settlement Agreement made
effective as of February 10, 1995 ("the Settlement Agreement"); and

         WHEREAS, Tropix was later acquired by and thereafter merged into AB
(f/k/a The Perkin-Elmer Corporation) and currently operates through Applera's
Applied Biosystems Group; and

         WHEREAS, DPC purchases PPD and TB Enhancer (both as defined in the
Settlement Agreement) from Lumigen; and

         WHEREAS, AB, Bronstein, Lumigen, Schaap and WSU, wish to amend the
Settlement Agreement as set forth in this First Amendment, and DPC, a guarantor
of Lumigen's payments to Tropix under the Settlement Agreement, wishes to be a
party to this First Amendment and to be bound by the covenants expressly set
forth herein;

         NOW, THEREFORE, in consideration of the mutual undertakings set forth
herein, the parties agree as follows:

         1. Unless the context of this First Amendment indicates otherwise,
capitalized terms used herein shall have the same meaning as defined in the
Settlement Agreement.

         2. AB covenants and agrees, on its own behalf, and on behalf of its
affiliates, parent and subsidiary corporations, predecessors (specifically
including Tropix), successors and assigns, not to institute any suit, action or
proceeding in any court, state or federal, U.S. or foreign, or in any patent
office or tribunal, against Lumigen, or DPC, or any of their suppliers,
customers, licensees, affiliates, subsidiary or parent corporations,
predecessors, successors or assigns, arising out of DPC's use or sale or its
customers' use or sale of TB Enhancer purchased by DPC from Lumigen in
conjunction with PPD purchased by DPC from Lumigen as an element of human in
vitro diagnostics or veterinary diagnostics. DPC is no longer required to
purchase from AB, DPC's requirements for PPD and TB Enhancer for veterinary
diagnostic immunoassays.
<PAGE>
         3. DPC agrees to pay to AB within thirty (30) days after the end of
each calendar quarter starting January 1, 2003 and ending upon the last to
expire of the Assigned Patent Rights, as defined in the Settlement Agreement, a
royalty equal to * % of DPC's sales of Kits of medical diagnostic and veterinary
reagents which are used in conjunction with PPD and TB Enhancer. The term Kit
shall mean and include any product or commercial test which is manufactured by
or on behalf of DPC and sold or otherwise commercially exploited by or on behalf
of DPC and delivered for use with PPD and TB Enhancer as an element of human in
vitro diagnostics or veterinary diagnostics. A Kit normally contains active
buffers, antibody/antigen/DNA/peptide, conjugate and substrate (PPD and
enhancers). As a basis for determining the royalty rate set forth above, DPC has
provided its applicable reagent sales during calendar years 2000, 2001, and 2002
(see Exhibit 1).

         4. Lumigen's obligation under Section 5.1 of the Settlement Agreement
to pay to AB a royalty equal to * percent ( * %) of Gross Revenues shall
continue; provided, however, that Lumigen shall exclude Gross Revenue derived
from the business of Lumigen with DPC as described in paragraph 2 above. This
exclusion shall continue in effect so long as DPC shall make the payments called
for in paragraph 3 above.

         5. Except as modified by the provisions of this First Amendment, all
terms contained in the Settlement Agreement shall continue in full force and
effect.

         IN WITNESS WHEREOF, the parties have caused this First Amendment to be
executed, corporate parties acting by and through their duly-authorized
officers, all on the day and date first above written.

                                          Applera Corporation
                                          through its Applied Biosystems Group

                                          By     /S/ Laura Lauman
                                             -----------------------------------
                                          Its      Vice President
                                             -----------------------------------

* Omitted pursuant to a request for
confidential treatment.  This material has         /S/ Irena Bronstein
been filed separately with the SEC.             --------------------------------
                                                Irena Bronstein

                                                Lumigen, Inc.

                                                 By      /S/ Gary T. Priestap
                                                   -----------------------------
                                                     Its  Vice President
                                                        ------------------------

                                       2
<PAGE>
                                                   /S/ A. Paul Schaap
                                                --------------------------------
                                                A. Paul Schaap

                                                Wayne State University

                                                By       /S/
                                                   -----------------------------
                                                     Its  Vice President/General
                                                          Counsel
                                                        ------------------------

                                                Diagnostic Products Corporation

                                                By       /S/ Michael Ziering
                                                   -----------------------------
                                                     Its  President
                                                        ------------------------

                                       3
<PAGE>
                                    EXHIBIT 1

              Lumigen Revenue with Diagnostic Products Corporation

                                November 7, 2002

<TABLE>
<CAPTION>
                       Total Lumigen           *% Royalty               DPC             *% Royalty
                          Revenue            paid to Tropix           Reagent          as a % of DPC
Year                      with DPC         from DPC business           Sales           Reagent Sales
----                      --------         -----------------           -----           -------------
<S>                    <C>                 <C>                      <C>                <C>
2000                         *                     *                 89,910,027             *%

2001                         *                     *                117,772,135             *%

2002 (est)                   *                     *                144,734,132             *%

2003 (projection)            *                     *                161,525,000             *%

4 year total                                       *                513,941,294             *%
</TABLE>

     * Omitted pursuant to a request for confidential
     treatment.  This material has been filed
     separately with the SEC
<PAGE>
                           CERTAIN DEFINITIONS USED IN
                     FIRST AMENDMENT TO SETTLEMENT AGREEMENT

         "PPD" shall mean 4-methoxy-4-(3-phosphatephenyl)spiro[1,2-dioxetane-3,
2-adamantane]disodium salt.

         "TB Enhancer" shall mean polyvinylbenzyltributylphosphonium chloride.

         "Assigned Patent Rights" shall mean the patents and patent applications
identified on Exhibit A attached hereto and any patents issuing from any such
patent applications, and any continuations, divisions, substitutions, reissues,
extensions and renewals of any of the foregoing.
<PAGE>
                                    EXHIBIT A

                             ASSIGNED PATENT RIGHTS

                                  U.S. PATENTS

                                    4,962,192
                                    4,959,182
                                    5,004,565
                                    5,386,017

                                U.S. APPLICATIONS

                                   06/887,139
                                   07/023,649
                                   07/265,890
                                   07/677,097
                                   08/020,302
                                   08/021,022
                                   08/186,461
                                   08/262,564
                                   08/339,085

                                 FOREIGN PATENTS

<TABLE>
<CAPTION>
                     Country                         Patent No.
                     -------                         ----------
<S>                 <C>                              <C>
                    Australia                          603,736
                      Korea                            69,259
                     Taiwan                            46,563
</TABLE>
<PAGE>
                           FOREIGN PATENT APPLICATIONS

<TABLE>
<CAPTION>
              Country                     Filing Date                           Serial No.
              -------                     -----------                           ----------
<S>                                       <C>                                   <C>
               Canada                        5/13/87                             537,003-5
               Canada                        9/21/93                             616,729-2
               Canada                        5/31/89                             601,376-7
               Canada                       12/20/89                             2,006,222

                Japan                        6/11/91                            236,758/91
                Japan                        6/11/91                            236,759/91
                Japan                        7/24/89                            191,247/89
                Japan                        6/29/93                            187,042/93
                Japan                       12/21/89                            502,424/89
                 *EPO                        6/23/87                            87108978.5
                 *EPO                       11/25/93                            93119049.0
                 *EPO                        7/24/89                            92109406.6
                 *EPO                        8/21/92                            92114339.2
                 *EPO                        7/24/89                            89113627.7
                 *EPO                       12/21/89                            89123690/3
                China                        7/27/89                            89106249.1
                China                        7/27/89                            93120975.7
                India                         9/6/89                            454/MAS/89
                India                         7/6/93                            457/MAS/93
</TABLE>

* Includes (1) any national applications filed on the basis of this application,
(2) all rights to file any national application in any state designated in this
application, and (3) all national and European patents issued and to issue based
on this application.<PAGE>

                                                                   Exhibit 4.6.2

            FIRST AMENDMENT TO CREDIT AGREEMENT AND PLEDGE AGREEMENT

            FIRST AMENDMENT TO CREDIT AGREEMENT AND PLEDGE AGREEMENT (this
"First Amendment"), dated as of September 3, 2004, among, TEXAS GENCO HOLDINGS,
INC., a Texas corporation (the "Parent"), TEXAS GENCO GP, LLC, a Texas limited
liability company ("Genco GP"), TEXAS GENCO LP, LLC, a Delaware limited
liability company ("Genco LP"), TEXAS GENCO SERVICES, LP, a Texas limited
partnership ("Genco Services"), TEXAS GENCO, LP, a Texas limited partnership
(the "Borrower"), the undersigned lenders party to the Credit Agreement referred
to below (the "Continuing Lenders") and DEUTSCHE BANK AG NEW YORK BRANCH, as
Administrative Agent and Collateral Agent (the "Administrative Agent"). All
capitalized terms used herein and not otherwise defined shall have the
respective meanings provided such terms in the Credit Agreement referred to
below immediately prior to the First Amendment Effective Date referred to below.

                              W I T N E S S E T H:

            WHEREAS, the Parent, Genco GP, Genco LP, Genco Services, the
Borrower, various lenders (the "Lenders"), the Documentation Agent and the
Administrative Agent are parties to a Credit Agreement, dated as of December 23,
2003 (the "Credit Agreement")

            WHEREAS, the Borrower and the Collateral Agent are parties to a
Pledge Agreement, dated as of December 23, 2003 (the "Pledge Agreement");

            WHEREAS, the parties hereto wish to effect the agreements and
amendments herein provided; and

            WHEREAS, subject to the terms and conditions of this First
Amendment, the parties hereto agree as follows:

I.    Amendments to the Credit Agreement as at the First Amendment Effective
      Date

            1. The first paragraph of the Credit Agreement is hereby amended by
deleting said paragraph in its entirety and inserting the following paragraph in
lieu thereof:

            "CREDIT AGREEMENT, dated as of December 23, 2003, among TEXAS GENCO
      HOLDINGS, INC., a Texas corporation (the "Parent"), TEXAS GENCO GP, LLC, a
      Texas limited liability company ("Genco GP"), TEXAS GENCO LP, LLC, a
      Delaware limited liability company ("Genco LP"), TEXAS GENCO SERVICES, LP,
      a Texas limited partnership ("Genco Services") TEXAS GENCO, LP, a Texas
      limited partnership (the "Borrower"), the Lenders from time to time party
      hereto, DEUTSCHE BANK AG NEW YORK BRANCH, as Administrative Agent and
      Collateral Agent, CITIBANK, N.A., as Syndication Agent and COMPASS BANK,
      as Documentation Agent. Unless otherwise defined herein, all capitalized
      terms used herein and defined in Section 11 are used herein as so
      defined."

<PAGE>

            2. Section 2.01(c) of the Credit Agreement is hereby amended by
inserting the following proviso at the end of clause (ii) of said Section:

            "; provided, that subject to Section 4.02(d), each South Texas
      Letter of Credit may have an expiry date occurring no later than the date
      occurring 360 days after the Maturity Date"

            3. Section 2.01(c) of the Credit Agreement is hereby further amended
by inserting the new sentence at the end of said Section:

            "(d) Notwithstanding anything to the contrary contained in this
      Agreement, any Security Document or any other Credit Document (i) subject
      to the provisions of Section 13.20, each of the covenants, agreements and
      Obligations of the Credit Parties contained in each Credit Document and
      (ii) the participations of each Lender in each Letter of Credit purchased
      by such Lender pursuant to Section 2.04, shall, in each case, remain in
      full force and effect until the expiration or termination of such Letter
      of Credit in accordance with its terms."

            4. Section 4.02 of the Credit Agreement is hereby amended by
inserting the following new clause (d) at the end of said Section:

            "(d) If any Letter of Credit is outstanding on the Maturity Date
      which has an expiry date later than the Maturity Date (or which, pursuant
      to its terms, may be extended to a date later than the Maturity Date) (all
      such Letters of Credit outstanding on the Maturity Date, the "Continuing
      Letters of Credit" and each, a "Continuing Letter of Credit"), the
      Borrower shall, on or prior the Maturity Date, (i) pay to each Issuing
      Lender which has issued any Continuing Letter of Credit an amount of cash
      equal to 105% of the aggregate Stated Amount of all Continuing Letters of
      Credit issued by such Issuing Lender to be held as security for all
      Obligations of the Borrower to such Issuing Lender in respect of such
      Continuing Letters of Credit in a cash collateral account to be
      established by, and under the sole dominion and control of, the respective
      Issuing Lender in accordance with the applicable Cash Collateral
      Agreement, (ii) enter into a Cash Collateral Agreement with each such
      Issuing Lender and take all other actions as may be reasonably requested
      by such Issuing Lender in connection with the foregoing and (iii) deliver
      to each such Issuing Lender an opinion from Baker Botts LLP covering (x)
      the creation and perfection of the security interests granted under the
      respective Cash Collateral Agreement and (y) and such other matters
      incidental to the transactions contemplated hereby as such Issuing Lender
      may reasonably request."

            5. Section 7.12(b) of the Credit Agreement is hereby amended by
deleting the last sentence thereof and inserting the following sentence in lieu
thereof:

            "At the time of the granting of any security interests pursuant to
      the Indenture the Borrower and/or such entity surviving the merger

                                      -2-
<PAGE>

      contemplated by the Genco LP Division, as the case may be, has good and
      marketable title to all Indenture Collateral referred to therein free and
      clear of all Liens (other than Permitted Liens)."

            6. Section 8.12 of the Credit Agreement is hereby amended by
deleting said Section in its entirety and inserting the following new Section
8.12 in lieu thereof:

      "Section 8.12 Future Guarantors. Each of the Credit Parties shall and
      shall cause each of its Subsidiaries to promptly upon any Person becoming
      a direct or indirect Subsidiary of the Parent to become a guarantor under
      the Guaranty by executing an accession agreement in respect of this
      Agreement in form and substance reasonably satisfactory to the
      Administrative Agent, provided that (x) no such Subsidiary that is not a
      Domestic Subsidiary shall be required to become a guarantor under the
      Guaranty, unless such Subsidiary shall at such time guarantee any
      Indebtedness of the Parent or any Domestic Subsidiary and (y) STP Nuclear
      Operating Company shall not be required to become a guarantor under the
      Guaranty."

            7. Section 9 of the Credit Agreement is hereby amended by inserting
the following new Section 9.10:

      "Section 9.10 Modifications to the Transaction Agreement. The Credit
      Parties shall not, and shall not permit, any modification or amendment to
      the Transaction Agreement which could reasonably be expected to (x) have a
      material adverse effect on the ability of any Credit Party to perform its
      payment obligations (including, without limitation, any obligations to
      post cash collateral pursuant to Section 4.02(d)) under this Agreement or
      any other Credit Document to which it is a party or (y) impair the rights
      of the Collateral Agent or the Lenders in the Collateral or the perfection
      or priority of the security interests granted or purported to be granted
      therein pursuant to the Security Documents."

            8. Section 10.03 of the Credit Agreement is hereby amended by
inserting the reference "Section 4.02(d)" immediately after the text "covenant
or agreement contained in" appearing in said Section.

            9. Section 11 of the Credit Agreement is hereby amended by deleting
the definitions of "Agents", "Applicable Commitment Commission Percentage" and
"Applicable Margin", "Bond", "Issuing Lender", "Lead Arranger", "Maturity Date"
and "Security Documents" in their entirety and inserting the following new
definitions of in lieu thereof:

            "Agents" shall mean and include (i) the Administrative Agent, (ii)
      the Collateral Agent, (iii) for the purposes of Section 12 only, the
      Documentation Agent and the Syndication Agent and (iv) for purposes of
      Sections 12, 13.01, 13.12 and 13.15 only, the Joint Lead Arrangers.

            "Applicable Commitment Commission Percentage" and "Applicable
      Margin" shall mean (x) with respect to Commitment Commission, a percentage

                                      -3-
<PAGE>

      per annum equal to 0.25% and (y) with respect to Loans maintained as (i)
      Eurodollar Loans, (a) at all times prior to the date upon which the
      requirements of Section 4.02(d) have been satisfied to the reasonable
      satisfaction of the Lenders, a percentage per annum equal to 1.00% and (b)
      at all times after the date upon which the requirements of Section 4.02(d)
      have been satisfied to the reasonable satisfaction of the Lenders, a
      percentage per annum equal to 0.50% and (ii) Base Rate Loans, a percentage
      per annum equal to 0.0%.

            "Bond" shall mean the bond in the original principal amount of the
      Total Commitment as in effect on the First Amendment Effective Date issued
      under the Indenture and pledged pursuant to the Pledge Agreement.

            "Issuing Lender" shall mean (x) solely in respect of the South Texas
      Letters of Credit, each of (i) DBAG for up to an aggregate Stated Amount
      with respect to all South Texas Letters of Credit issued by DBAG equal to
      50% of all South Texas Letters of Credit and (ii) Citibank for up to an
      aggregate Stated Amount with respect to all South Texas Letters of Credit
      issued by Citibank equal to 50% of all South Texas Letters of Credit, (y)
      in respect of all Letters of Credit (other than the South Texas Letters of
      Credit), Compass for up to an aggregate Stated Amount equal to the
      difference of Total Commitment and the aggregate Stated Amount of all
      South Texas Letters of Credit and (z) any other Lender which at the
      request of the Borrower and with the consent of the Administrative Agent
      (which shall not be unreasonably withheld or delayed) agrees, in such
      Lender's sole discretion, to become an Issuing Lender for the purpose of
      issuing Letters of Credit pursuant to Section 2 (which, in each case, for
      purposes of this definition shall also include any respective banking
      affiliate of DBAG, Citibank, Compass and such other Lender). It being
      understood and agreed that on the First Amendment Effective Date the sole
      Issuing Lenders are DBAG, Citibank and Compass (and their respective
      banking affiliates).

            "Joint Lead Arrangers" shall mean Deutsche Bank Securities Inc. and
      Citigroup Global Markets Inc., in their capacity as Joint Lead Arrangers.

            "Maturity Date" shall mean the earlier of (x) date occurring 180
      days after the First Amendment Effective Date and (y) the Non-STP
      Acquisition Date.

            "Security Documents" shall mean (subject to Section 13.20), the
      Indenture and any supplemental indenture issued to the Administrative
      Agent in connection with the Bond, the Bond, Pledge Agreement, each Cash
      Collateral Agreement, and each other collateral document or instrument
      entered into pursuant to Section 5.05 or 8.11, if any, in each case as and
      when delivered in accordance with this Agreement as same may be amended,
      modified or supplemented from time to time in accordance with the terms
      thereof and/or hereof.

            10. Section 11 of the Credit Agreement is hereby further amended by
adding the following definitions in such Section in their appropriate
alphabetical order:

                                      -4-
<PAGE>

            "Citibank" shall mean Citibank, N.A., in its individual capacity.

            "Cash Collateral Agreement" shall mean a cash collateral agreement
substantially in the form of Exhibit J.

            "Compass" shall mean Compass Bank, in its individual capacity.

            "Continuing Letter of Credit" shall have the meaning provided in
Section 4.02(d).

            "First Amendment Effective Date" shall mean the date upon which the
      First Amendment to this Agreement, dated September 3, 2004 becomes
      effective in accordance with its terms.

            "Genco LP Division" shall have the meaning provided in the
      Transaction Agreement.

            "Genco LP Division Date" shall mean the earlier of (x) date upon
      which the Genco LP Division is consummated in accordance with the
      Transaction Agreement and (y) the date upon which Non-STP Assets are no
      longer owned by the Borrower.

            "Highest Lawful Rate" shall mean, with respect to each Lender, the
      Administrative Agent and the Documentation Agent, the maximum nonusurious
      interest rate, if any, that at any time or from time to time may be
      contracted for, taken, reserved, charged or received with respect to any
      Loan or on other amounts, if any, due to such Person pursuant to this
      Agreement or any other Credit Document under applicable law. "Applicable
      law" as used in this definition means, with respect to each Lender, the
      Administrative Agent and the Documentation Agent, that law in effect from
      time to time that permits the charging and collection by such Person of
      the highest permissible lawful, nonusurious rate of interest on the
      transactions herein contemplated under the laws of Texas.

            "Non-STP Acquisition" shall have the meaning provided in the
      Transaction Agreement.

            "Non-STP Acquisition Date" shall mean the earlier of (x) the date
      upon which the Non-STP Acquisition is consummated in accordance with the
      terms of the Transaction Agreement and (y) the date upon which Non-STP
      Assets are no longer owned by any Credit Party.

            "Non-STP Assets" shall have the meaning provided in the Transaction
      Agreement.

            "Overnight Bridge Loan" shall have the meaning provided in the
      Transaction Agreement.

            "Public Company Merger" shall have the meaning provided in the
      Transaction Agreement.

                                      -5-
<PAGE>

            "Repurchase" shall have the meaning provided in Section 13.18.

            "South Texas Letter of Credit" shall mean each Letter of Credit
      issued by (x) DBAG (in its capacity as an Issuing Lender) and (y) Citibank
      (in its capacity as an Issuing Lender), in each case, in connection with
      the Borrower's acquisition of an increased ownership interest in the South
      Texas Project; provided that (i) the aggregate Stated Amount of all South
      Texas Letters of Credit shall not exceed $189,500,000 and (ii) neither
      DBAG nor Citibank shall be required to issue a South Texas Letter of
      Credit in a Stated Amount exceeding 50% of the aggregate Stated Amount of
      all such South Texas Letters of Credit as provided in clause (i) of this
      proviso. For the avoidance of doubt, it is understood that nothing
      contained in this definition shall be deemed to increase the Commitments
      of DBAG or Citibank or limit or modify the provisions contained in Section
      2.01(c) or the definition of Issuing Lender.

            "South Texas Project" shall mean the South Texas Project Nuclear
      Electric Generating Station.

            "Syndication Agent" shall mean Citibank in its capacity as
      Syndication Agent.

            "Transaction Agreement" shall mean that certain Transaction
      Agreement, dated as of July 21, 2004, among CenterPoint Energy, Utility
      Holding, LLC, NN Houston Sub, Inc., the Parent, HPC Merger Sub, Inc. and
      GC Power Acquisition LLC and shall include all exhibits thereto, in each
      case, as previously delivered to the Lenders and as may be amended from
      time to time in accordance with the terms thereof and with the terms of
      this Agreement.

            11. The definition of the term "Permitted Liens" appearing in
Section 11 of the Credit Agreement is hereby amended by deleting the amount
"$250,000,000" appearing therein and inserting the amount "$425,000,000" in lieu
thereof.

            12. Section 12.01 of the Credit Agreement is hereby amended by
deleting the first sentence thereof and inserting the following text in lieu
thereof.

            "The Lenders hereby designate (i) DBAG as Administrative Agent and
      Collateral Agent to act as specified herein and in the other Credit
      Documents, (ii) Compass Bank as Documentation Agent, (ii) Citibank, N.A.,
      as Syndication Agent and (iii) Deutsche Bank Securities, Inc. and
      Citigroup Global Markets Inc. as Joint Lead Arrangers, in each case to act
      as specified herein and in the other Credit Documents."

            13. Section 12.10 of the Credit Agreement is hereby amended by
deleting said Section in its entirety and inserting the following new Section
12.10 in lieu thereof:

            12.10 Documentation Agent; Syndication Agent. Notwithstanding
      anything to the contrary contained herein, nothing in this Agreement shall
      impose on either the Documentation Agent, in such capacity or the
      Syndication Agent, in such capacity, any duties or obligations.

                                      -6-
<PAGE>

            14. Section 13.02 of the Credit Agreement is hereby amended by
inserting the text "or its Affiliates" immediately after the text "any time held
or owing by such Lender" appearing in said Section.

            15. Section 13 of the Credit Agreement is hereby amended by adding
the following new Sections 13.17, 13.18, 13.19, 13.20 and 13.21 at the end of
said Section:

            "Section 13.17 Genco LP Division. Notwithstanding anything to the
      contrary contained in the Credit Agreement or any other Credit Document,
      the Continuing Lenders hereby agree that the Genco LP Division shall be
      permitted in accordance with the terms and conditions contained in the
      Transaction Agreement; provided that on or prior to the Genco LP Division
      Date, the following conditions shall have been satisfied, in each case, to
      the reasonable satisfaction of the Lenders:

            (a) (i) Texas Genco, LP shall survive the merger contemplated by the
      Genco LP Division, (ii) at no time shall the Credit Agreement or any other
      Credit Document cease to be in full force and effect as to Texas Genco,
      LP, (iii) the Credit Agreement and each other Credit Document shall remain
      in full force and effect as to the Borrower (after giving effect to such
      merger);

            (b) each surviving entity of the merger contemplated by the Genco LP
      Division (other than the Borrower) shall (i) pursuant to documentation in
      form and substance reasonably satisfactory to the Lenders, become a party
      to the Credit Agreement as a Guarantor thereunder and expressly agree to
      assume all obligations and liabilities of a Guarantor thereunder
      (including, without limitation, the Guaranteed Obligations) and under each
      of the other Credit Documents and (ii) take all actions and deliver all
      documents, agreements and opinions reasonably requested by the Lenders in
      connection with the assumption of such obligations and liabilities
      including, without limitation, those actions and documents described in
      Section 5 of the Credit Agreement, as if such Person were a Guarantor on
      the Effective Date;

            (c) the requirements and conditions contained in the Indenture in
      connection with the Genco LP Division and the merger contemplated thereby
      (including, without limitation, Articles Twelve and Thirteen thereof)
      shall have been satisfied in all material respects in accordance therewith
      and no such requirement or condition shall have been waived without the
      express written consent of the Lenders;

            (d) the Administrative Agent shall have received evidence of the
      completion of all other recordings and filings of, or with respect to, the
      Indenture as may be necessary or, in the reasonable opinion of the
      Administrative Agent, desirable to effectively to create a valid and
      enforceable first priority mortgage Lien (subject to Permitted Liens) and
      otherwise perfect the security interests purported to be created by the
      Indenture (after giving effect to the Genco LP Division); and

                                      -7-
<PAGE>

            (e) the Administrative Agent and the Lenders shall have received a
      copy of the opinions of Baker Botts LLP and the Deputy General Counsel of
      CenterPoint Energy issued to the Trustee in connection with any actions
      contemplated by the Genco LP Division and a reliance letter addressed to
      the Administrative Agent and each of the Lenders in respect of each such
      opinion.

            Section 13.18 Public Company Merger. Notwithstanding anything to the
      contrary contained in the Credit Agreement or any other Credit Document,
      the Continuing Lenders hereby agree that the Public Company Merger and the
      payments made in connection with the repurchase (the "Repurchase") of any
      outstanding Common Stock of the Parent shall be permitted in accordance
      with the terms and conditions contained in the Transaction Agreement;
      provided that (i) the Parent shall survive the Public Company Merger (and
      there shall be no other surviving entity of such merger), (ii) at no time
      shall the obligations of the Parent under the Guaranty cease to be in full
      force and effect, (iii) the Guaranty and each other Credit Document shall
      remain in full force and effect as to the Parent (after giving effect to
      such merger), (iv) the Overnight Bridge Loans constitute the unsecured
      Indebtedness of the Parent guaranteed by the Parent's Domestic
      Subsidiaries (which guaranty shall not be secured), (v) all payments in
      respect of the Repurchase shall be made solely from the proceeds of the
      Overnight Bridge Loan, the proceeds of the Non-STP Acquisition and/or the
      cash on hand of the Parent and its Subsidiaries and (vi) the Overnight
      Bridge Loans shall only be repaid with a portion of the proceeds of the
      Non-STP Acquisition in accordance with Section 2.3(c) of the Transaction
      Agreement.

            Section 13.19 Non-STP Acquisition. Notwithstanding anything to the
      contrary contained in the Credit Agreement or any other Credit Document
      and subject to the definition of Maturity Date, the Lenders hereby agree
      that the Non-STP Acquisition shall be permitted in accordance with the
      terms and conditions contained in the Transaction Agreement, provided that
      concurrently with or prior to the Non-STP Acquisition Date, (i) all of the
      requirements of Section 4.02(d) have been satisfied to the reasonable
      satisfaction of the Lenders and (ii) the Total Commitment shall have been
      terminated, no Revolving Note, Loan, Unpaid Drawing or any Letter of
      Credit which has not been cash collateralized to the reasonable
      satisfaction of the Lenders in accordance with Section 4.02(d) is
      outstanding and all other Obligations (other than indemnities described in
      Section 13.13, and any other indemnities set forth in any other Credit
      Document which survive the termination of the Total Commitment, in each
      case which are not then due and payable) shall have been paid in full in
      cash.

            Section 13.20 Termination of the Guaranty, the Pledge Agreement and
      Certain Covenants and Events of Default Upon Cash Collateralization. The
      Lenders hereby agree that, notwithstanding anything to the contrary
      contained in this Agreement or any other Credit Document and without
      limiting any other provision of this Agreement, upon the satisfaction of
      the requirements contained in Section 4.02(d) to the reasonable
      satisfaction of the Lenders:

            (a) except for the covenants contained in Section 8.01(a), (b), (d)
      and (k), Section 8.02, 8.04 and 8.11 and Section 9.07, all other covenants
      contained in Section 8

                                      -8-
<PAGE>

      and Section 9 and the covenants contained in Section 4.02(a) shall be of
      no further force and effect and no breach of such covenants shall
      constitute a Default or Event of Default under this Agreement or any other
      Credit Document;

            (b) the occurrence of any of the events described in Sections 10.04,
      10.06, 10.07, 10.08, 10.09 and 10.11 shall, in each case, no longer
      constitute Events of Default under the Credit Agreement or any other
      Credit Document;

            (c) the Guaranty shall terminate and be of no further force and
      effect; and

            (d) the Pledge Agreement shall terminate in accordance with its
      terms.

            13.21. Limitation on Interest. Notwithstanding anything to the
      contrary contained in this Agreement or any other Credit Document, all
      agreements between the Borrower, the Administrative Agent or any Lender,
      whether now existing or hereafter arising and whether written or oral, are
      hereby expressly limited so that in no contingency or event whatsoever,
      whether by reason of demand being made in respect of an amount due under
      any Credit Document or otherwise, shall the amount paid, or agreed to be
      paid, to the Administrative Agent or any Lender for the use, forbearance,
      or detention of the money to be loaned under this Agreement, any Revolving
      Notes or any other Credit Document or otherwise or for the payment or
      performance of any covenant or obligation contained herein or in any other
      Credit Document exceed the Highest Lawful Rate. If, as a result of any
      circumstances whatsoever, fulfillment of any provision hereof or of any of
      such documents, at the time performance of such provision shall be due,
      shall involve transcending the limit of validity prescribed by Applicable
      Law, then, ipso facto, the obligation to be fulfilled shall be reduced to
      the limit of such validity, and if, from any such circumstance, the
      Administrative Agent or any Lender shall ever receive interest under
      Applicable Law that would exceed the Highest Lawful Rate, such amount that
      would exceed the Highest Lawful Rate shall be applied to the reduction of
      the principal amount owing on account of such Lender's Loans or the
      amounts owing on other obligations of the Borrower to the Administrative
      Agent or any Lender under any Credit Document and not to the payment of
      interest, or if such excessive interest exceeds the unpaid principal
      balance of such Lender's Loans and the amounts owing on other obligations
      of the Borrower to the Administrative Agent or any Lender under any Credit
      Document, as the case may be, such excess shall be refunded to the
      Borrower to the extent required under Applicable Law. All sums paid or
      agreed to be paid to the Administrative Agent or any Lender for the use,
      forbearance or detention of the indebtedness of the Borrower to the
      Administrative Agent or any Lender shall, to the fullest extent permitted
      by Applicable Law, be amortized, prorated, allocated and spread throughout
      the full term of such indebtedness until payment in full of the principal
      (including the period of any renewal or extension thereof) so that the
      interest on account of such indebtedness shall not exceed the Highest
      Lawful Rate. Notwithstanding anything to the contrary contained in any
      Credit Document, it is understood and agreed that if at any time the rate
      of interest that accrues on the outstanding principal balance of any Loan
      shall exceed the Highest Lawful Rate, the rate of interest that accrues on
      the outstanding principal

                                      -9-
<PAGE>

      balance of any Loan shall be limited to the Highest Lawful Rate, but any
      subsequent reductions in the rate of interest that accrues on the
      outstanding principal balance of any Loan shall not reduce the rate of
      interest that accrues on the outstanding principal balance of any Loan
      below the Highest Lawful Rate until the total amount of interest accrued
      on the outstanding principal balance of any Loan equals the amount of
      interest that would have accrued if such interest rate had at all times
      been in effect."

            16. Schedule I to the Credit Agreement is hereby amended by deleting
Schedule I to the Credit Agreement in its entirety and replacing it with
Schedule I attached hereto.

            17. Schedule II to the Credit Agreement is hereby amended by
deleting Schedule II to the Credit Agreement in its entirety and replacing it
with Schedule II attached hereto.

            18. The Credit Agreement is hereby further amended by inserting new
Exhibit J in the form of Exhibit J attached hereto.

            19. The cover page to the Credit Agreement is hereby amended by (i)
deleting the text ", AS LEAD ARRANGER AND BOOK RUNNER" immediately following the
text "DEUTSCHE BANK SECURITIES INC.", and inserting the text "and CITIGROUP
GLOBAL MARKETS INC., AS JOINT LEAD ARRANGERS AND BOOK RUNNERS" in lieu thereof,
(ii) inserting the text "CITIBANK, N.A., as Syndication Agent" immediately below
the text "as Administrative Agent and Collateral Agent" and (iii) deleting the
amount "$75,000,000" appearing therein and replacing it with the amount
"$250,000,000".

II.   Amendments to the Pledge Agreement as at the First Amendment Effective
      Date

            1. Clause (b) of Section 1 to the Pledge Agreement is hereby amended
by deleting the definition of "Pledged Bonds" in its entirety and inserting the
following definition in lieu thereof:

            ""Pledged Bonds": shall mean the First Mortgage Indenture Bonds
      Series C, initially authenticated and delivered in the aggregate principal
      amount of two hundred fifty million dollars ($250,000,000), established in
      the Third Supplemental Indenture, dated as of September 3, 2004, between
      the Company and the Trustee."

            2. Section 21 of the Pledge Agreement is hereby amended by inserting
the following new text immediately after the text "Letter of Credit" appearing
in said Section:

            "which has not been cash collateralized to the reasonable
      satisfaction of the Lenders in accordance with Section 4.02(d) of the
      Credit Agreement"

III.  Agreements

            1. The parties hereto agree that upon the effectiveness of this
First Amendment, each Person set forth on Schedule III hereto (each a
"Non-Continuing Lender" and collectively, the "Non-Continuing Lenders") shall no
longer constitute a "Lender" under the

                                      -10-
<PAGE>

Credit Agreement, except with respect to indemnification provisions applicable
to such Non-Continuing Lender under any Credit Document.

            2. Concurrently with the effectiveness of this First Amendment, the
Borrower agrees that in connection with the amendment made in Section 15 of
Article I hereof and the agreements made in Section 1 of this Article III and
notwithstanding anything to the contrary contained in the Credit Agreement, the
Borrower shall take all actions as may be reasonably necessary to ensure that
all Lenders (after giving effect to this First Amendment) participate in each
Borrowing of Loans outstanding on the First Amendment Effective Date on a pro
rata basis including, without limitation, by making such voluntary repayments of
outstanding Loans and the incurring such new Loans as necessary to ensure the
foregoing (even though as a result thereof Lenders may incur costs of the type
described in Section 1.11 which costs shall be for the account of, and paid by,
the Lender on the First Amendment Effective Date).

            3. Each of the Parent, Genco GP, Genco LP and Genco Services hereby
represents and warrants that, subject to Section 13.20 of the Credit Agreement
(after giving effect to this First Amendment), (i) it has full power and
authority, and has taken all action necessary, to execute and deliver this First
Amendment and to continue the guarantees made by it under the Guaranty (after
giving effect to this First Amendment), (ii) it is and shall continue to be on
and after the First Amendment Effective Date, bound by the provisions of the
Guaranty and each other Credit Document to which it is a party (except to the
extent that the enforcement thereof may be limited by applicable bankruptcy,
insolvency, reorganization or other similar laws affecting creditors' rights
generally and by equity principles), (iii) on and after the First Amendment
Effective Date, it continues to be a Guarantor for all purposes under the
Guaranty and each other Credit Document, (iv) on and after the First Amendment
Effective Date, it will continue to obtain benefits from the incurrence of Loans
to, and the issuance of Letters of Credit for the account of, the Borrower, (v)
on and after the First Amendment Effective Date and after giving effect to
clause (vi) below, the guarantees made by it under the Guaranty remain in full
force and effect and (vi) on and after the First Amendment Effective Date all
references in the Guaranty and each other Credit Document to the "Credit
Agreement" shall be deemed and are references to the Credit Agreement as amended
hereby.

            4. The Borrower hereby represents, warrants and agrees that (i) it
has full power and authority, and has taken all action necessary, to execute and
deliver this First Amendment and to continue the pledge and grant of security
interests made by it under the Pledge Agreement and each other Security Document
(after giving effect to this First Amendment), (ii) subject to Section 13.20 of
the Credit Agreement (after giving effect to this First Amendment), it is and
shall continue to be on and after the First Amendment Effective Date, bound by
the provisions of the Pledge Agreement and each other Credit Document to which
it is a party, (iii) on and after the First Amendment Effective Date and after
giving effect to clause (iv) below, the Pledge Agreement remains in full force
and effect and (iv) on and after the First Amendment Effective Date all
references in each Security Document to the "Credit Agreement" shall be deemed
and are references to the Credit Agreement as amended hereby.

                                      -11-
<PAGE>

IV.   Miscellaneous

            1. In order to induce the undersigned Lenders to enter into this
First Amendment, the Borrower hereby represents and warrants that (x) no Default
or Event of Default exists on the First Amendment Effective Date both before and
after giving effect to this First Amendment, and (y) all of the representations
and warranties contained in the Credit Agreement are true and correct in all
material respects on the First Amendment Effective Date, both before and after
giving effect to this First Amendment, with the same effect as though such
representations and warranties had been made on and as of the First Amendment
Effective Date (unless such representations expressly relate to an earlier date,
in which case they shall be true and correct in all material respects on and as
of such earlier date).

            2. This First Amendment is limited as specified and shall not
constitute a modification, acceptance or waiver of any other provision of the
Credit Agreement or any other Credit Document.

            3. This First Amendment may be executed in any number of
counterparts and by the different parties hereto on separate counterparts, each
of which counterparts when executed and delivered shall be an original, but all
of which shall together constitute one and the same instrument. A complete set
of counterparts shall be lodged with the Borrower and the Administrative Agent.

            4. THIS FIRST AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF THE
PARTIES HEREUNDER SHALL BE CONSTRUED IN ACCORDANCE WITH AND BE GOVERNED BY THE
LAWS OF THE STATE OF NEW YORK.

            5. This First Amendment shall become effective on the date (the
"First Amendment Effective Date") when:

            (A) the Borrower and each Continuing Lender shall have signed a
counterpart hereof (whether the same or different counterparts) and shall have
delivered (including by way of telecopier) the same to the Administrative Agent;

            (B) there shall have been delivered to the Administrative Agent for
the account of each Lender that has requested same, the appropriate Revolving
Note executed by the Borrower, in each case in the amount, maturity and as
otherwise provided in the Credit Agreement (after giving effect to this First
Amendment);

            (C) the Commitments of each Non-Continuing Lender shall have been
terminated and the Obligations due and payable to the Non-Continuing Lenders on
the First Amendment Effective Date shall have been paid in full;

            (D) on the First Amendment Effective Date, all reasonable costs,
fees and expenses (including, without limitation, the reasonable legal fees and
expenses of White & Case LLP) payable to the Lead Arrangers, the Agents and the
Lenders shall have been paid in full;

                                      -12-
<PAGE>

            (E) the Administrative Agent shall have received executed copies of,
(i) the Third Supplemental Indenture, dated September 3, 2004, between the
Borrower and the Trustee in the form of Exhibit A hereto (the "Third
Supplemental Indenture"), (ii) the Officer's Certificate of Genco GP, dated
September 3, 2004, in form of Exhibit B hereto, (iii) the Company Order, dated
September 3, 2004, from the Borrower to the Trustee, in the form of Exhibit C
hereto, (iv) the opinion of Baker Botts LLP issued to the Trustee in connection
with any of the transactions contemplated by this First Amendment and a reliance
letter addressed to the Administrative Agent and each of the Lenders in respect
of such opinion and (v) any all other documents required under the Indenture;

            (F) the Borrower shall have delivered to the Collateral Agent, the
First Mortgage Bond Series C, in the aggregate principal amount of two hundred
fifty million dollars;

            (G) the Administrative Agent shall have received legal opinions
addressed to each Agent and the Lenders from (i) New York counsel opinion of
Baker Botts LLP, (ii) the Deputy General Counsel of CenterPoint Energy and (iii)
local counsel opinion of Baker Botts LLP, and, in each case covering matters,
reasonably acceptable to the Administrative Agent including, without limitation,
(x) a no-conflicts opinion as to (1) the material Indebtedness for Borrowed
Money of any Credit Party which will remain outstanding of the First Amendment
Effective Date (if any) and (2) any material contracts of Parent or its
subsidiaries, (y) title, perfection and priority of the security interests
securing the Bond and (z) and such other matters incidental to the transactions
contemplated hereby as the Administrative Agent may reasonably request;

            (H) the Administrative Agent shall have received a certificate,
dated the First Amendment Effective Date, and signed on behalf of the Borrower
by a Responsible Officer, stating that all conditions in this Section 5 (other
than clause (H)) of this First Amendment have been satisfied on such date;

            (I) the Administrative Agent shall have received evidence of the
completion of all other recordings and filings of, or with respect to, the
Indenture as may be necessary or, in the reasonable opinion of the
Administrative Agent, desirable to effectively to create a valid and enforceable
first priority mortgage Lien (subject to Permitted Liens) and otherwise perfect
the security interests purported to be created by the Indenture;

            (J) since December 31, 2003, nothing shall have occurred (and
neither the Administrative Agent nor any Lender shall have become aware of any
facts or conditions not previously known) which the Administrative Agent or the
Required Lenders shall determine could reasonably be expected to have a Material
Adverse Effect;

            (K) on or prior to the First Amendment Effective Date, all necessary
governmental (domestic and foreign) and third party approvals and/or consents in
connection with the transactions contemplated by the Credit Documents (after
giving effect to this First Amendment) shall have been obtained and remain in
effect, and all applicable waiting periods shall have expired without any action
being taken by any

                                      -13-
<PAGE>

competent authority which in the reasonable judgment of the Administrative Agent
or the Required Lenders restrains, prevents or imposes materially adverse
conditions upon the consummation of the transactions contemplated by the Credit
Documents. Additionally, there shall not exist any judgment, order, injunction
or other restraint issued or filed or a hearing seeking injunctive relief or
other restraint pending or notified prohibiting or imposing materially adverse
conditions upon the making of any Loan, issuance of any Letter of Credit or the
consummation of the transactions contemplated by the Credit Documents;

            (L) on the First Amendment Effective Date, no litigation by any
entity (private or governmental) shall be pending or threatened with respect to
this Agreement, any other Credit Document or any other documentation executed in
connection herewith and therewith or the transactions contemplated hereby and
thereby, or which the Administrative Agent or the Required Lenders shall
determine has had, or could reasonably be expected to have, a Material Adverse
Effect; and

            (M) the Administrative Agent shall have received evidence that all
other actions necessary or, in the reasonable opinion of the Administrative
Agent, desirable to perfect and protect the security interests purported to be
created by the Indenture (after giving effect to this First Amendment) have been
taken.

            6. From and after the First Amendment Effective Date all references
in the Credit Agreement and the other Credit Documents to the Credit Agreement
shall be deemed to be references to the Credit Agreement as modified hereby.
Except as modified hereunder, the terms, provisions and conditions of the Credit
Agreement and the other Credit Documents shall continue in full force and
effect.

                                    * * * * *

                                      -14-
<PAGE>

            IN WITNESS WHEREOF, each of the parties hereto has caused a
counterpart of this First Amendment to be duly executed and delivered as of the
date first above written.

                                             TEXAS GENCO, LP

                                             By: TEXAS GENCO GP, LLC,
                                                 its General Partner

                                             By: /s/ MARC KILBRIDE
                                                -------------------------------
                                                Name: Marc Kilbride
                                                Title: V.P. and Treasurer

                                             TEXAS GENCO HOLDINGS, INC.

                                             By: /s/ MARC KILBRIDE
                                                -------------------------------
                                                Name: Marc Kilbride
                                                Title: V.P. and Treasurer

                                             TEXAS GENCO GP, LLC

                                             By: /s/ MARC KILBRIDE
                                                -------------------------------
                                                Name: Marc Kilbride
                                                Title: V.P. and Treasurer

                                             TEXAS GENCO LP, LLC

                                             By: /s/ PATRICIA F. GENZEL
                                                -------------------------------
                                                Name: Patricia F. Genzel
                                                Title: Manager and President

<PAGE>

                                                TEXAS GENCO SERVICES , LP

                                             By: TEXAS GENCO GP, LLC,
                                                 its General Partner

                                             By: /s/ MARC KILBRIDE
                                                -------------------------------
                                                Name: Marc Kilbride
                                                Title: V.P. and Treasurer

<PAGE>

                                             DEUTSCHE BANK AG NEW YORK
                                             BRANCH, individually and as
                                             Administrative Agent and
                                             Collateral Agent

                                             By: /s/ RICHARD HENSHALL
                                                -------------------------------
                                                Name: Richard Henshall
                                                Title: Director

                                             By: /s/ OLIVER RIEDINGER
                                                -------------------------------
                                                Name: Oliver Riedinger
                                                Title: Vice President

<PAGE>

                                             CITIBANK, N.A.

                                             By: /s/ SANDIP SEN
                                                --------------------------------
                                                Name:  Sandip Sen
                                                Title: Managing Director

<PAGE>

                                             COMPASS BANK

                                             By: /s/ COLLIS SANDERS
                                                --------------------------------
                                                Name:  Collis Sanders
                                                Title: Executive Vice President

<PAGE>

                                                                      SCHEDULE I
                                   COMMITMENTS

<TABLE>
<CAPTION>
Lender                                                     Commitment
------                                                    ------------
<S>                                                       <C>
Deutsche Bank AG New York Branch                          $110,000,000
Citibank N.A.                                             $110,000,000
Compass Bank                                              $ 30,000,000

                                                Total:    $250,000,000
                                                          ============
</TABLE>

<PAGE>

                                                                     SCHEDULE II

                                LENDER ADDRESSES

DEUTSCHE BANK AG NEW YORK BRANCH
60 Wall Street
New York, NY 10005-2858
Telephone: (212) 250-3968
Facsimile: (212) 797-4346
Attention: Richard Henshall

CITIBANK, N.A.
2 Penns Way, Suite 110
New Castle, DE  19720
Telephone: (302) 894-6084
Facsimile: (212) 994-0847
Attention: Karen Riley

COMPASS BANK
24 Greenway Plaza, Suite 1400
Houston, TX  77046
Telephone: (713) 968-8234
Facsimile: (713) 968-8211
Attention: Collis Sanders

<PAGE>
                                                                    SCHEDULE III

                             NON-CONTINUING LENDERS

Bank of America, N.A.

Credit Suisse First Boston

JPMorgan Chase Bank

Wachovia Bank, National Association

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