SUPPLEMENTAL INDENTURE NO. 13

SUPPLEMENTAL INDENTURE No. 13, dated as of May 15, 2008, between CENTERPOINT ENERGY RESOURCES CORP., a Delaware corporation formerly known as NorAm Energy Corp. (the “Company”), and THE BANK OF NEW YORK TRUST COMPANY, NATIONAL ASSOCIATION (successor to JPMorgan Chase Bank, National Association (formerly Chase Bank of Texas, National Association)), as Trustee (the “Trustee”).

The Company has heretofore executed and delivered to the Trustee an Indenture, dated as of February 1, 1998 (the “Original Indenture” and, as previously and hereby supplemented and amended, the “Indenture”), providing for the issuance from time to time of one or more series of the Company’s Securities.

The Company has changed its name from “NorAm Energy Corp.” to “CenterPoint Energy Resources Corp.” and all references in the Indenture to the “Company” or “NorAm Energy Corp.” shall be deemed to refer to CenterPoint Energy Resources Corp.

Pursuant to the terms of the Indenture, the Company desires to provide for the establishment of a new series of Securities to be designated as the “6.00% Senior Notes due 2018” (the “Notes”), the form and substance of such Notes and the terms, provisions and conditions thereof to be set forth as provided in the Original Indenture and this Supplemental Indenture No. 13.

Section 301 of the Original Indenture provides that various matters with respect to any series of Securities issued under the Indenture may be established in an indenture supplemental to the Indenture.

Subparagraph (7) of Section 901 of the Original Indenture provides that the Company and the Trustee may enter into an indenture supplemental to the Indenture to establish the form or terms of Securities of any series as permitted by Sections 201 and 301 of the Original Indenture.

For and in consideration of the premises and the issuance of the series of Securities provided for herein, it is mutually covenanted and agreed, for the equal and proportionate benefit of the Holders of the Securities of such series, as follows:

Section 101.   Relation to Indenture .  This Supplemental Indenture No. 13 constitutes an integral part of the Original Indenture.

Section 102.   Additional Definitions .  For all purposes of this Supplemental Indenture  No. 13:

Capitalized terms used herein shall have the meaning specified herein or in the Original Indenture, as the case may be;

“Acquired Entity” has the meaning set forth in Section 303(k) hereof;

“Capital Lease” means a lease that, in accordance with accounting principles generally accepted in the United States of America, would be recorded as a capital lease on the balance sheet of the lessee;

“Comparable Treasury Yield” has the meaning set forth in Section 402(a) hereof;

“Consolidated Net Tangible Assets” means the total amount of assets of the Company and its Subsidiaries less, without duplication: (a) total current liabilities (excluding indebtedness due within 12 months); (b) all reserves for depreciation and other asset valuation reserves, but excluding reserves for deferred federal income taxes; (c) all intangible assets such as goodwill, trademarks, trade names, patents and unamortized debt discount and expense carried as an asset; and (d) all appropriate adjustments on account of minority interests of other Persons holding common stock of any Subsidiary, all as reflected in the Company’s most recent audited consolidated balance sheet preceding the date of such determination;

“Corporate Trust Office” means the principal office of the Trustee at which at any particular time its corporate trust business shall be administered, as follows: (a) for payment, registration and transfer of the Securities: 2001 Bryan Street, 9th Floor, Dallas, Texas 75201, Attention: Bondholder Communications; telephone (214) 672-5125 or (800) 275-2048; telecopy: (214) 672-5873; and (b) for all other communications relating to the Securities: 601 Travis Street, 18th Floor, Houston, Texas 77002, Attention: Global Corporate Trust; telephone: (713) 483-6817; telecopy: (713) 483-7038;

“Equity Interests” means any capital stock, partnership, joint venture, member or limited liability or unlimited liability company interest, beneficial interest in a trust or similar entity or other equity interest or investment of whatever nature;

“Funded Debt” has the meaning set forth in Section 304 hereof.

“H.15 Statistical Release” has the meaning set forth in Section 402(b) hereof;

The term “indebtedness,” as applied to the Company or any Subsidiary, means bonds, debentures, notes and other instruments or arrangements representing obligations created or assumed by any such corporation, including any and all:  (i) obligations for money borrowed

(other than unamortized debt discount or premium); (ii) obligations evidenced by a note or similar instrument given in connection with the acquisition of any business, properties or assets of any kind; (iii) obligations as lessee under a Capital Lease; and (iv) any amendments, renewals, extensions, modifications and refundings of any such indebtedness or obligation listed in clause (i), (ii) or (iii) above.  All indebtedness secured by a lien upon property owned by the Company or any Subsidiary and upon which indebtedness any such corporation customarily pays interest, although any such corporation has not assumed or become liable for the payment of such indebtedness, shall for all purposes hereof be deemed to be indebtedness of any such corporation.  All indebtedness for borrowed money incurred by other Persons which is directly guaranteed as to payment of principal by the Company or any Subsidiary shall for all purposes hereof be deemed to be indebtedness of the Company or any such Subsidiary, as applicable, but no other contingent obligation of the Company or any such Subsidiary in respect of indebtedness incurred by other Persons shall for any purpose be deemed to be indebtedness of the Company or any such Subsidiary;

“Independent Investment Banker” has the meaning set forth in Section 401(c) hereof;

“Interest Payment Date” has the meaning set forth in Section 204(a) hereof;

“Issue Date” has the meaning set forth in Section 204(a) hereof;

“lien” or “liens” have the meanings set forth in Section 303 hereof;

“Long-Term Indebtedness” means, collectively, the Company’s outstanding:

(a) 7.875% Senior Notes due 2013, (b) 5.95% Senior Notes due 2014, and (c) any long-term indebtedness (but excluding for this purpose any long-term indebtedness incurred pursuant to any revolving credit facility, letter of credit facility or other similar bank credit facility) of the Company issued subsequent to the issuance of the Notes and prior to the Termination Date containing covenants substantially similar to the covenants set forth in Sections 303 and 304 hereof, or an event of default substantially similar to the event of default set forth in Section 501(a) hereof, but not containing a provision substantially similar to the provision set forth in Section 305 hereof;

“Make-Whole Premium” has the meaning set forth in Section 401(b) hereof;

“Maturity Date” has the meaning set forth in Section 203 hereof;

“Non-Recourse Debt” means (i) any indebtedness for borrowed money incurred by any Project Finance Subsidiary to finance the acquisition, improvement, installation, design, engineering, construction, development, completion, maintenance or operation of, or otherwise to pay costs and expenses relating to or providing financing for, any project, which indebtedness for borrowed money does not provide for recourse against the Company or any Subsidiary of the Company (other than a Project Finance Subsidiary and such recourse as exists under a Performance Guaranty) or any property or asset of the Company or any Subsidiary of the Company (other than Equity Interests in, or the property or assets of, a Project Finance Subsidiary and such recourse as exists under a Performance Guaranty) and (ii) any refinancing of such indebtedness for borrowed money that does not increase the outstanding principal amount thereof (other than to pay costs incurred in connection therewith and the capitalization of any

interest or fees) at the time of the refinancing or increase the property subject to any lien securing such indebtedness for borrowed money or otherwise add additional security or support for such indebtedness for borrowed money.

“Notes” has the meaning set forth in the third paragraph of the Recitals hereof;

“Original Indenture” has the meaning set forth in the first paragraph of the Recitals hereof;

“Performance Guaranty” means any guaranty issued in connection with any Non-Recourse Debt that (i) if secured, is secured only by assets of or Equity Interests in a Project Finance Subsidiary, and (ii) guarantees to the provider of such Non-Recourse Debt or any other person (a) performance of the improvement, installation, design, engineering, construction, acquisition, development, completion, maintenance or operation of, or otherwise affects any such act in respect of, all or any portion of the project that is financed by such Non-Recourse Debt, (b) completion of the minimum agreed equity or other contributions or support to the relevant Project Finance Subsidiary, or (c) performance by a Project Finance Subsidiary of obligations to persons other than the provider of such Non-Recourse Debt.

“Principal Property” means any natural gas distribution property, natural gas pipeline or gas processing plant located in the United States, except any such property that in the opinion of the Board of Directors is not of material importance to the total business conducted by the Company and its consolidated Subsidiaries.  “Principal Property” shall not include any oil or gas property or the production or proceeds of production from an oil or gas producing property or the production or any proceeds of production of gas processing plants or oil or gas or petroleum products in any pipeline or storage field;

“Project Finance Subsidiary” means any Subsidiary designated by the Company whose principal purpose is to incur Non-Recourse Debt and/or construct, lease, own or operate the assets financed thereby, or to become a direct or indirect partner, member or other equity participant or owner in a Person created for such purpose, and substantially all the assets of which Subsidiary or Person are limited to (x) those assets being financed (or to be financed), or the operation of which is being financed (or to be financed), in whole or in part by Non-Recourse Debt, or (y) Equity Interests in, or indebtedness or other obligations of, one or more other such Subsidiaries or Persons, or (z) indebtedness or other obligations of the Company or any Subsidiary or other Persons.  At the time of designation of any Project Finance Subsidiary, the sum of the net book value of the assets of such Subsidiary and the net book value of the assets of all other Project Finance Subsidiaries then existing shall not in the aggregate exceed 10 percent of Consolidated Net Tangible Assets.

“Redemption Price” has the meaning set forth in Section 401(a) hereof;

“Regular Record Date” has the meaning set forth in Section 204(b) hereof;

“Remaining Term” has the meaning set forth in Section 402(a) hereof;

“Sale and Leaseback Transaction” means any arrangement entered into by the Company or any Subsidiary with any Person providing for the leasing to the Company or any Subsidiary of

any Principal Property (except for temporary leases for a term, including any renewal thereof, of not more than three years and except for leases between the Company and a Subsidiary or between Subsidiaries), which Principal Property has been or is to be sold or transferred by the Company or such Subsidiary to such Person;

“Significant Subsidiary” means any Subsidiary of the Company, other than a Project Finance Subsidiary, that is a “significant subsidiary” as defined in Rule 1-02 of Regulation S-X under the Securities Act of 1933 and the Securities Exchange Act of 1934, as such regulation is in effect on the date of issuance of the Notes.

“Subsidiary” of any entity means any corporation, partnership, joint venture, limited liability company, trust or estate of which (or in which) more than 50% of (i) the issued and outstanding capital stock having ordinary voting power to elect a majority of the Board of Directors of such corporation (irrespective of whether at the time capital stock of any other class or classes of such corporation shall or might have voting power upon the occurrence of any contingency), (ii) the interest in the capital or profits of such limited liability company, partnership, joint venture or other entity or (iii) the beneficial interest in such trust or estate is at the time directly or indirectly owned or controlled by such entity, by such entity and one or more of its other subsidiaries or by one or more of such entity’s other subsidiaries.

“Termination Date” has the meaning set forth in Section 305.

“Value” with respect to a Sale and Leaseback Transaction has the meaning set forth in Section 303 hereof;

All references herein to Articles and Sections, unless otherwise specified, refer to the corresponding Articles and Sections of this Supplemental Indenture No. 13; and

The terms “herein,” “hereof,” “hereunder” and other words of similar import refer to this Supplemental Indenture No. 13.

Section 201.   Title of the Securities. The Notes shall be designated as the “6.00% Senior Notes due 2018.”

Section 202.   Limitation on Aggregate Principal Amount.   The Trustee shall authenticate and deliver the Notes for original issue on the Issue Date in the aggregate principal amount of $300,000,000 upon a Company Order for the authentication and delivery thereof and satisfaction of Sections 301 and 303 of the Original Indenture.  Such order shall specify the amount of the Notes to be authenticated, the date on which the original issue of Notes is to be authenticated and the name or names of the initial Holder or Holders.  The aggregate principal amount of Notes that may initially be outstanding shall not exceed $300,000,000; provided , however , that the authorized aggregate principal amount of the Notes may be increased above such amount by a Board Resolution to such effect.

Section 203.   Stated Maturity.   The Stated Maturity of the Notes shall be May 15, 2018 (the “Maturity Date”).

Section 204.   Interest and Interest Rates .

(a)           The Notes shall bear interest at the rate of 6.00% per annum, from and including May 15, 2008 (the “Issue Date”) to, but excluding, the Maturity Date.  Such interest shall be payable semiannually in arrears, on May 15 and November 15, of each year (each such date, an “Interest Payment Date”), commencing November 15, 2008.

(b)           The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date shall be paid to the Persons in whose names the Notes (or one or more Predecessor Securities) are registered at the close of business on the immediately preceding May 1 and November 1, respectively, whether or not such day is a Business Day (each such date, a “Regular Record Date”).  Any such interest not so punctually paid or duly provided for shall forthwith cease to be payable to the Holder on such Regular Record Date and shall either (i) be paid to the Person in whose name such Note (or one or more Predecessor Securities) is registered at the close of business on the Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of the Notes not less than 10 days prior to such Special Record Date, or (ii) be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange or automated quotation system on which the Notes may be listed or traded, and upon such notice as may be required by such exchange or automated quotation system, all as more fully provided in the Indenture.

(c)           The amount of interest payable for any period shall be computed on the basis of a 360-day year of twelve 30-day months. The amount of interest payable for any partial period shall be computed on the basis of a 360-day year of twelve 30-day months and the days elapsed in any partial month. In the event that any date on which interest is payable on a Note is not a Business Day, then a payment of the interest payable on such date will be made on the next succeeding day which is a Business Day (and without any interest or other payment in respect of any such delay) with the same force and effect as if made on the date the payment was originally payable.

(d)           Any principal and premium, if any, and any installment of interest, which is overdue shall bear interest at the rate of 6.00% per annum (to the extent permitted by law), from the dates such amounts are due until they are paid or made available for payment, and such interest shall be payable on demand.

Section 205.   Place of Payment.   The Trustee shall initially serve as the Paying Agent for the Notes.  The Place of Payment where the Notes may be presented or surrendered for payment shall be the Corporate Trust Office of the Trustee.

Section 206.   Place of Registration or Exchange; Notices and Demands With Respect to the Notes.   The place where the Holders of the Notes may present the Notes for registration of transfer or exchange and may make notices and demands to or upon the Company in respect of the Notes shall be the Corporate Trust Office of the Trustee.

Section 207.   Percentage of Principal Amount.   The Notes shall be initially issued at 99.171% of their principal amount plus accrued interest, if any, from May 15, 2008.

Section 208.   Global Securities.   The Notes shall be issuable in whole or in part in the form of one or more Global Securities.  Such Global Securities shall be deposited with, or on behalf of, The Depository Trust Company, New York, New York, which shall act as Depositary with respect to the

Notes.  Such Global Securities shall bear the legends set forth in the form of Security attached as Exhibit A hereto.

Section 209.   Form of Securities.   The Notes shall be substantially in the form attached as Exhibit A hereto.

Section 210.   Securities Registrar.   The Trustee shall initially serve as the Security Registrar for the Notes.

Section 211.   Defeasance and Discharge; Covenant Defeasance .

(a)           Article Fourteen of the Original Indenture, including without limitation, Sections 1402 and 1403 (as modified by Section 211(b) hereof) thereof, shall apply to the Notes.

(b)           Solely with respect to the Notes issued hereby, the first sentence of Section 1403 of the Original Indenture is hereby deleted in its entirety, and the following is substituted in lieu thereof:

“Upon the Company’s exercise of its option (if any) to have this Section applied to any Securities or any series of Securities, as the case may be, (1) the Company shall be released from its obligations under Article Eight and under any covenants provided pursuant to Section 301(20), 901(2) or 901(7) for the benefit of the Holders of such Securities, including, without limitation, the covenants provided for in Article Three of Supplemental Indenture No. 13 to the Indenture, and (2) the occurrence of any event specified in Sections 501(4) (with respect to Article Eight and to any such covenants provided pursuant to Section 301(20), 901(2) or 901(7)) and 501(7) shall be deemed not to be or result in an Event of Default, in each case with respect to such Securities as provided in this Section on and after the date the conditions set forth in Section 1404 are satisfied (hereinafter called “Covenant Defeasance”).”

Section 212.   Sinking Fund Obligations.   The Company shall have no obligation to redeem or purchase any Notes pursuant to any sinking fund or analogous requirement or upon the happening of a specified event or at the option of a Holder thereof.

Section 301.   Maintenance of Properties.   The Company shall cause all properties used or useful in the conduct of its business or the business of any Subsidiary to be maintained and kept in good condition, repair and working order and supplied with all necessary equipment and shall cause to be made all necessary repairs, renewals, replacements, betterments and improvements thereof, all as in the judgment of the Company may be necessary so that the business carried on in connection therewith may be properly conducted at all times; provided , however , that nothing in this Section shall prevent the Company from discontinuing the operation or maintenance of any of such properties if such discontinuance is, in the judgment of the Company, desirable in the conduct of its business or the business of any Subsidiary.

Section 302.   Payment of Taxes and Other Claims.   The Company shall pay or discharge or cause to be paid or discharged, before the same shall become delinquent, (1) all taxes, assessments and governmental charges levied or imposed upon the Company or any Subsidiary or upon the income, profits or property of the Company or any Subsidiary, and (2) all lawful claims for labor, materials and supplies which, if unpaid, might by law become a lien upon the property of the Company or any Subsidiary; provided , however , that the Company shall not be required to pay or discharge or cause to be paid or discharged any such tax, assessment, charge or claim whose amount, applicability or validity is being contested in good faith by appropriate proceedings.

Section 303.   Restrictions on Liens.   The Company shall not pledge, mortgage or hypothecate, or permit to exist, and shall not cause, suffer or permit any Subsidiary to pledge, mortgage or hypothecate, or permit to exist, except in favor of the Company or any Subsidiary, any mortgage, deed of trust, pledge, hypothecation, assignment, deposit arrangement, charge, security interest, encumbrance or lien of any kind whatsoever (including any Capital Lease) (collectively, a “lien” or “liens”) upon, any Principal Property or any Equity Interest in any Significant Subsidiary owning any Principal Property, at any time owned by it or a Subsidiary, to secure any indebtedness, without making effective provisions whereby the Notes shall be equally and ratably secured with or prior to any and all such indebtedness and any other indebtedness similarly entitled to be equally and ratably secured; provided , however , that this provision shall not apply to or prevent the creation or existence of:

(a)           undetermined or inchoate liens and charges incidental to construction, maintenance, development or operation;

(b)           the lien of taxes and assessments for the then current year;

(c)           the lien of taxes and assessments not at the time delinquent;

(d)           the lien of specified taxes and assessments which are delinquent but the validity of which is being contested at the time by the Company or such Subsidiary in good faith and by appropriate proceedings;

(e)           any obligations or duties, affecting the property of the Company or such Subsidiary, to any municipality or public authority with respect to any franchise, grant, license, permit or similar arrangement;

(f)           the liens of any judgments or attachment in an aggregate amount not in excess of $10,000,000, or the lien of any judgment or attachment the execution or enforcement of which has been stayed or which has been appealed and secured, if necessary, by the filing of an appeal bond;

(g)           any lien on any property held or used by the Company or a Subsidiary in connection with the exploration for, development of or production of oil, gas, natural gas (including liquefied gas and storage gas), other hydrocarbons, helium, coal, metals, minerals, steam, timber, geothermal or other natural res