TENTH SUPPLEMENTAL INDENTURE

Exhibit 4.2

MISSISSIPPI POWER COMPANY

TO

WELLS FARGO BANK, NATIONAL ASSOCIATION

TRUSTEE

TENTH SUPPLEMENTAL INDENTURE

DATED AS OF MARCH 6, 2009

SERIES 2009A 5.55% SENIOR NOTES

DUE MARCH 1, 2019

TABLE OF CONTENTS ¹

_________________________

¹  Table of Contents does not constitute part of the Indenture or have any bearing upon the interpretation of any of its terms and provisions.

i

THIS TENTH SUPPLEMENTAL INDENTURE is made as of the 6 ^th day of March, 2009 by and between MISSISSIPPI POWER COMPANY, a Mississippi corporation, 2992 West Beach Boulevard, Gulfport, Mississippi 39501 (the “Company”), and WELLS FARGO BANK, NATIONAL ASSOCIATION, a national banking association, 7000 Central Parkway, Suite 550, Atlanta, Georgia 30328 (the “Trustee”).

W I T N E S S E T H:

WHEREAS, the Company has heretofore entered into a Senior Note Indenture, dated as of May 1, 1998 (the “Original Indenture”), with Wells Fargo Bank, National Association, as successor Trustee, as heretofore supplemented;

WHEREAS, the Original Indenture is incorporated herein by this reference and the Original Indenture, as heretofore supplemented and as further supplemented by this Tenth Supplemental Indenture, is herein called the “Indenture”;

WHEREAS, under the Original Indenture, a new series of Senior Notes may at any time be established pursuant to a supplemental indenture executed by the Company and the Trustee;

WHEREAS, the Company proposes to create under the Indenture a new series of Senior Notes;

WHEREAS, additional Senior Notes of other series hereafter established, except as may be limited in the Original Indenture as at the time supplemented and modified, may be issued from time to time pursuant to the Indenture as at the time supplemented and modified; and

WHEREAS, all conditions necessary to authorize the execution and delivery of this Tenth Supplemental Indenture and to make it a valid and binding obligation of the Company have been done or performed.

NOW, THEREFORE, in consideration of the agreements and obligations set forth herein and for other good and valuable consideration, the sufficiency of which is hereby acknowledged, the parties hereto hereby agree as follows:

ARTICLE 1

Series 2009A Senior Notes

SECTION 101. Establishment . There is hereby established a new series of Senior Notes to be issued under the Indenture, to be designated as the Company’s Series 2009A 5.55% Senior Notes due March 1, 2019 (the “Series 2009A Notes”).

There are to be authenticated and delivered $125,000,000 principal amount of Series 2009A Notes, and such principal amount of the Series 2009A Notes may be increased from time to time pursuant to Section 301 of the Original Indenture. All Series 2009A Notes need not be issued at the

same time and such series may be reopened at any time, without the consent of the Holders thereof, for issuance of additional Series 2009A Notes. Any such additional Series 2009A Notes will have the same interest rate, maturity and other terms as those initially issued. No Series 2009A Notes shall be authenticated and delivered except as provided by Sections 203, 303, 304, 907 and 1107 of the Original Indenture. The Series 2009A Notes shall be issued in definitive fully registered form.

The Series 2009A Notes shall be issued in the form of one or more Global Securities in substantially the form set out in Exhibit A hereto. The Depositary with respect to the Series 2009A Notes shall be The Depository Trust Company.

The form of the Trustee’s Certificate of Authentication for the Series 2009A Notes shall be in substantially the form set forth in Exhibit B hereto.

Each Series 2009A Note shall be dated the date of authentication thereof and shall bear interest from the date of original issuance thereof or from the most recent Interest Payment Date to which interest has been paid or duly provided for.

SECTION 102. Definitions . The following defined terms used herein shall, unless the context otherwise requires, have the meanings specified below. Capitalized terms used herein for which no definition is provided herein shall have the meanings set forth in the Original Indenture.

“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 Series 2009A Notes to be redeemed 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 Series 2009A Notes.

“Comparable Treasury Price” means, with respect to any Redemption Date, (i) the average of the Reference Treasury Dealer Quotations for such Redemption Date, after excluding the highest and lowest such Reference Treasury Dealer Quotations, or (ii) if the Company obtains fewer than four such Reference Treasury Dealer Quotations, the average of all such quotations.

“Independent Investment Banker” means an independent investment banking institution of national standing appointed by the Company.

“Interest Payment Dates” means March 1 and September 1 of each year, commencing September 1, 2009.

“Reference Treasury Dealer” means a primary United States Government securities dealer in New York City appointed by the Company.

2

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

“Regular Record Date” means, with respect to each Interest Payment Date, the close of business on the 15th calendar day preceding such Interest Payment Date (whether or not a Business Day).

“Treasury Yield” 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.

SECTION 103. Payment of Principal and Interest . The principal of the Series 2009A Notes shall be due at Stated Maturity (unless earlier redeemed). The unpaid principal amount of the Series 2009A Notes shall bear interest at the rate of 5.55% per annum until paid or duly provided for. Interest shall be paid semi-annually in arrears on each Interest Payment Date to the Person in whose name the Series 2009A Notes are registered on the Regular Record Date for such Interest Payment Date, provided that interest payable at the Stated Maturity or on a Redemption Date as provided herein will be paid to the Person to whom principal is payable. Any such interest that is not so punctually paid or duly provided for will forthwith cease to be payable to the Holders on such Regular Record Date and may either be paid to the Person or Persons in whose name the Series 2009A Notes are 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 the Series 2009A Notes not less than ten (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, if any, on which the Series 2009A Notes shall be listed, and upon such notice as may be required by any such exchange, all as more fully provided in the Original Indenture.

Payments of interest on the Series 2009A Notes will include interest accrued to but excluding the respective Interest Payment Dates. Interest payments for the Series 2009A Notes shall be computed and paid on the basis of a 360-day year of twelve 30-day months. In the event that any date on which interest is payable on the Series 2009A Notes is not a Business Day, then a payment of the interest payable on such date will be made on the next succeeding day that 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.

Payment of the principal and interest due at the Stated Maturity or earlier redemption of the Series 2009A Notes shall be made upon surrender of the Series 2009A Notes at the Corporate Trust Office of the Trustee. The principal of and interest on the Series 2009A Notes shall be paid in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts. Payments of interest (including interest on any Interest

3

Payment Date) will be made, subject to such surrender where applicable, at the option of the Company, (i) by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register or (ii) by wire transfer or other electronic transfer at such place and to such account at a banking institution in the United States as may be designated in writing to the Trustee at least sixteen (16) days prior to the date for payment by the Person entitled thereto.

SECTION 104. Denominations . The Series 2009A Notes may be issued in the denominations of $1,000, or any integral multiple thereof.

SECTION 105. Global Securities . The Series 2009A Notes will be issued in the form of one or more Global Securities registered in the name of the Depositary (which shall be The Depository Trust Company) or its nominee. Except under the limited circumstances described below, Series 2009A Notes represented by one or more Global Securities will not be exchangeable for, and will not otherwise be issuable as, Series 2009A Notes in definitive form. The Global Securities described above may not be transferred except by the Depositary to a nominee of the Depositary or by a nominee of the Depositary to the Depositary or another nominee of the Depositary or to a successor Depositary or its nominee.

Owners of beneficial interests in such a Global Security will not be considered the Holders thereof for any purpose under the Indenture, and no Global Security representing a Series 2009A Note shall be exchangeable, except for another Global Security of like denomination and tenor to be registered in the name of the Depositary or its nominee or to a successor Depositary or its nominee. The rights of Holders of such Global Security shall be exercised only through the Depositary.

Neither the Company, the Trustee nor any agent of the Company or the Trustee shall have any responsibility or liability for any aspect of the records relating to or payments made on account of beneficial ownership interests in a Global Security or for maintaining, supervising or reviewing any records relating to such beneficial ownership interests.

Subject to the procedures of the Depositary, a Global Security shall be exchangeable for Series 2009A Notes registered in the names of persons other than the Depositary or its nominee only if (i) the Depositary notifies the Company that it is unwilling or unable to continue as a Depositary for such Global Security and no successor Depositary shall have been appointed by the Company, or if at any time the Depositary ceases to be a clearing agency registered under the Securities Exchange Act of 1934, as amended, at a time when the Depositary is required to be so registered to act as such Depositary and no successor Depositary shall have been appointed by the Company, in each case within 90 days after the Company receives such notice or becomes aware of such cessation, (ii) the Company in its sole discretion determines that such Global Security shall be so exchangeable, or (iii) there shall have occurred an Event of Default with respect to the Series 2009A Notes. Any Global Security that is exchangeable pursuant to the preceding sentence shall be exchangeable for Series 2009A Notes registered in such names as the Depositary shall direct.

SECTION 106. Transfer . No service charge will be made for any transfer or exchange of Series 2009A Notes, but payment will be required of a sum sufficient to cover any tax or other governmental charge that may be imposed in connection therewith. The Company shall not be required (a) to issue, register the transfer of or exchange any Series