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                                                                     EXHIBIT 4.3

                                 TRUST AGREEMENT

         THIS TRUST AGREEMENT is made as of June 30, 2000, by and between
Southern Energy, Inc., a Delaware corporation, as Depositor (the "Depositor"),
and Bankers Trust (Delaware), duly organized and existing in the State of
Delaware, as Trustee (the "Trustee"). The Depositor and the Trustee hereby agree
as follows:

         1.       The trust created hereby shall be known as "SEI Trust I", in
which name the Trustee, or the Depositor to the extent provided herein, may
conduct the business of the Trust, make and execute contracts, and sue and be
sued.

         2.       The Depositor hereby assigns, transfers, conveys and sets over
to the Trustee the sum of $10. The Trustee hereby acknowledges receipt of such
amount in trust from the Depositor, which amount shall constitute the initial
trust estate. The Trustee hereby declares that it will hold the trust estate in
trust for the Depositor. It is the intention of the parties hereto that the
Trust created hereby constitute a business trust under Chapter 38 of Title 12 of
the Delaware Code, 12 Del. C. ss. 3801, et seq. (the "Business Trust Act"), and
that this document constitute the governing instrument of the Trust. The Trustee
is hereby authorized and directed to execute and file a certificate of trust
with the Delaware Secretary of State substantially in the form attached hereto
or in such other form as the Trustee may approve.

         3.       The Depositor and the Trustee will enter into an amended and
restated Trust Agreement satisfactory to each such party and substantially in
the form included as an exhibit to the Registration Statement on Form S-1 (the
"1933 Act Registration Statement") referred to below, or in such other form as
the Trustee and the Depositor may approve, to provide for the contemplated
operation of the Trust created hereby and the issuance of the Preferred
Securities and Common Securities referred to therein. Prior to the execution and
delivery of such amended and restated Trust Agreement, the Trustee shall not
have any duty or obligation hereunder or with respect to the trust estate,
except as otherwise required by applicable law or as may be necessary to obtain
prior to such execution and delivery any licenses, consents or approvals
required by applicable law or otherwise. However, notwithstanding the foregoing,
the Trustee may take all actions deemed proper as are necessary to effect the
transactions contemplated herein.

         4.       The Depositor and the Trustee hereby authorize and direct the
Depositor, as the sponsor of the Trust, (i) to file with the Securities and
Exchange Commission (the "Commission") and execute, in the case of the 1933 Act
Registration Statement and 1934 Act Registration Statement (as herein defined),
on behalf of the Trust, (a) the 1933 Act Registration Statement including
pre-effective or post-effective amendments to such Registration Statement,
relating to the registration under the Securities Act of 1933, as amended (the
"1933 Act"), of the Preferred Securities of the Trust, (b) any preliminary
prospectus or prospectus or supplement thereto relating to the Preferred
Securities required to be filed pursuant to Rule 424 under the 1933 Act, and (c)
a Registration Statement on Form 8-A or other appropriate form (the "1934 Act
Registration Statement") (including all pre-effective and post-effective
amendments thereto) relating to the registration of the Preferred Securities of
the Trust under Section 12(b) of the Securities Exchange Act of 1934, as
amended; (ii)


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to file with the New York Stock Exchange and execute on behalf of the Trust a
listing application and all other applications, statements, certificates,
agreements and other instruments as shall be necessary or desirable to cause the
Preferred Securities to be listed on the New York Stock Exchange; (iii) to file
and execute on behalf of the Trust such applications, reports, surety bonds,
irrevocable consents, appointments of attorney for service of process and other
papers and documents as shall be necessary or desirable to register the
Preferred Securities under the securities or "Blue Sky" laws of such
jurisdictions as the Depositor, on behalf of the Trust, may deem necessary or
desirable; and (iv) to execute, deliver and perform on behalf of the Trust an
underwriting agreement with the Depositor and the underwriter or underwriters of
the Preferred Securities of the Trust. The Trustee further hereby ratifies and
approves all actions having previously been taken with respect to the foregoing.
In the event that any filing referred to in clauses (i)-(iii) above is required
by the rules and regulations of the Commission, the New York Stock Exchange or
state securities or Blue Sky laws to be executed on behalf of the Trust by the
Trustee, Bankers Trust (Delaware), in its capacity as Trustee of the Trust, is
hereby authorized and directed to join in any such filing and to execute on
behalf of the Trust any and all of the foregoing, it being understood that
Bankers Trust (Delaware) in its capacity as Trustee of the Trust shall not be
required to join in any such filing or execute on behalf of the Trust any such
document unless required by the rules and regulations of the Commission, the New
York Stock Exchange or state securities or Blue Sky laws.

         5.       This Trust Agreement may be executed in one or more
counterparts.

         6.       The number of Trustees initially shall be one (1) and
thereafter the number of Trustees shall be such number as shall be fixed from
time to time by a written instrument signed by the Depositor which may increase
or decrease the number of Trustees; provided, however, that to the extent
required by the Business Trust Act, one Trustee shall either be a natural person
who is a resident of the State of Delaware or, if not a natural person, an
entity which has its principal place of business in the State of Delaware.
Subject to the foregoing, the Depositor is entitled to appoint or remove without
cause any Trustee at any time. Any Trustee may resign upon thirty days' prior
notice to the Depositor.

         7.       This Trust Agreement shall be construed in accordance with and
governed by the internal laws of the State of Delaware without regard to its
conflicts of law principles.


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

                                    SOUTHERN ENERGY, INC.,
                                        as Depositor

                                    By:
                                             -----------------------------------
                                             Elizabeth B. Chandler
                                             Vice President and Secretary


                                    BANKERS TRUST (DELAWARE),
                                             not in its individual capacity
                                             but solely as Trustee


                                    By:
                                             -----------------------------------
                                             M. Lisa Wilkins
                                             Assistant Vice President


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