<PAGE>

                                                                    EXHIBIT 4.16

                                                                  EXECUTION COPY


                       SOUTHERN ENERGY MID-ATLANTIC, LLC

                                 $1,224,000,000

                              PASS THROUGH TRUSTS

           Pass Through Certificates, Series A, Series B and Series C

                         REGISTRATION RIGHTS AGREEMENT
                         -----------------------------


                                                               December 18, 2000

CREDIT SUISSE FIRST BOSTON CORPORATION,
 as representative of the several Purchasers

c/o Credit Suisse First Boston Corporation,
Eleven Madison Avenue
New York, NY  10010-3629

Dear Sirs:

          Southern Energy Mid-Atlantic, LLC, a Delaware limited liability
company (the "Company") an indirect wholly-owned subsidiary of Southern Energy,
              -------
Inc., a Delaware corporation ("SEI"), proposes, subject to the terms and
conditions stated in a purchase agreement dated December 7, 2000 (the "Purchase
                                                                       --------
Agreement"), that State Street Bank and Trust Company of Connecticut, National
---------
Association, acting not in its individual capacity but solely as trustee (in its
capacity as such trustee, including its successors and assigns and any successor
trustee, the "Pass Through Trustee") under each of the Pass Through Trust
              --------------------
Agreements (the "Pass Through Trust Agreements") dated as of December 18, 2000
                 -----------------------------
between the Company and the Pass Through Trustee, will issue and sell to Credit
Suisse First Boston Corporation ("CSFB"), Banc of America Securities LLC ("B of
                                  ----                                     ----
A"), Chase Securities Inc. ("Chase"), and UBS Warburg LLC ("UBS" and, together
-                            -----                          ---
with CSFB, B of A and Chase, the several "Purchasers") 8.625% Pass Through
                                          ----------
Certificates, Series A in the aggregate amount of $454,000,000, 9.125% Pass
Through Certificates, Series B in the aggregate amount of $435,000,000, and
10.060% Pass Through Certificates, Series C in the aggregate amount of
$335,000,000 (such Pass Through Certificates are herein referred to as the
"Initial Securities").  Capitalized terms used herein but not defined herein
-------------------
shall have the respective meanings specified in the Purchase Agreement whether
expressly set forth therein or by reference to another agreement.  As an
inducement to the Purchasers to enter into the Purchase Agreement, the Company
agrees with the Purchasers, for the benefit of the Purchasers and the holders of
the Securities (as defined below) (collectively, the "Holders"), as follows:
                                                      -------

<PAGE>

          SECTION 1.  Exchange Offer.  Unless not permitted by applicable law
                      --------------
(after the Company has complied with the ultimate paragraph of this Section 1),
the Company shall prepare and file with the United States Securities and
Exchange Commission (the "Commission") a registration statement (the "Exchange
                          ----------                                  --------
Offer Registration Statement") on an appropriate form under the Securities Act
----------------------------
of 1933, as amended, and the rules and regulations of the Commission promulgated
thereunder (the "Securities Act"), with respect to a proposed offer (the
                 --------------
"Exchange Offer") to the holders of Transfer Restricted Securities (as defined
---------------
herein) who are not prohibited by any law or policy of the Commission from
participating in the Exchange Offer, to exchange a like aggregate principal
amount of pass-through certificates otherwise in all material respects identical
to the Initial Securities and registered under the Securities Act (the "Exchange
                                                                        --------
Securities").  The Company shall use its reasonable best efforts to (i) cause
----------
such Exchange Offer Registration Statement to become effective under the
Securities Act no later than the date 325 days after the date (the "Funding
                                                                    -------
Date") on which the Purchasers purchase the Initial Securities pursuant to the
----
Purchase Agreement (the "Effective Date") and (ii)  keep the Exchange Offer
                         --------------
Registration Statement effective for not less than 30 days (or longer, if
required by applicable law) after the date notice of the Exchange Offer is
mailed to the holders (such period being called the "Exchange Offer Registration
                                                     ---------------------------
Period").
------

          If the Company commences the Exchange Offer, the Company (i) will be
entitled to consummate the Exchange Offer 30 days after such commencement
(provided that the Company has accepted all the Initial Securities theretofore
validly tendered in accordance with the terms of the Exchange Offer) and (ii)
will be required to consummate the Exchange Offer no later than 40 days after
the date on which the Exchange Offer Registration Statement is declared
effective (such 40th day being the "Consummation Deadline").
                                    ---------------------

          Following the declaration of the effectiveness of the Exchange Offer
Registration Statement, the Company shall promptly commence the Exchange Offer,
it being the objective of such Exchange Offer to enable each Holder of Transfer
Restricted Securities electing to exchange the Initial Securities for Exchange
Securities (assuming that such Holder is not an affiliate of the Company within
the meaning of the Securities Act, acquires the Exchange Securities in the
ordinary course of such Holder's business and has no arrangements with any
person to participate in the distribution of the Exchange Securities and is not
prohibited by any law or policy of the Commission from participating in the
Exchange Offer) to trade such Exchange Securities from and after their receipt
without any limitations or restrictions under the Securities Act and without
material restrictions under the securities laws of the several states of the
United States.

          The Company and the Purchasers acknowledge that, pursuant to current
interpretations by the Commission's staff of Section 5 of the Securities Act, in
the absence of an applicable exemption therefrom, (i) each Holder which is a
broker-dealer electing to exchange Initial Securities, acquired for its own
account as a result of market making activities or other trading activities, for
Exchange Securities (an "Exchanging Dealer"), is required to deliver a
                         -----------------
prospectus containing the information set forth in (a)

                                       2
<PAGE>

Annex A hereto on the cover, (b) Annex B hereto in the "Exchange Offer
Procedures" section and the "Purpose of the Exchange Offer" section, and (c)
Annex C hereto in the "Plan of Distribution" section of such prospectus in
connection with a sale of any such Exchange Securities received by such
Exchanging Dealer pursuant to the Exchange Offer and (ii) a Purchaser that
elects to sell Securities acquired in exchange for Initial Securities
constituting any portion of an unsold allotment, is required to deliver a
prospectus containing the information required by Items 507 or 508 of Regulation
S-K under the Securities Act, as applicable, in connection with such sale.

          The Company shall use its reasonable best efforts to keep the Exchange
Offer Registration Statement effective and to amend and supplement the
prospectus contained therein, in order to permit such prospectus to be delivered
by all persons subject to the prospectus delivery requirements of the Securities
Act for such period of time as such persons must comply with such requirements
in order to resell the Exchange Securities; provided, however, that (i) in the
                                            --------  -------
case where such prospectus and any amendment or supplement thereto must be
delivered by an Exchanging Dealer or a Purchaser, such period shall be the
lesser of 180 days and the date on which all Exchanging Dealers and the
Purchasers have sold all Exchange Securities held by them (unless such period is
extended pursuant to Section 3(j) below) and (ii) the Company shall make such
prospectus and any amendment or supplement thereto available to any broker-
dealer for use in connection with any resale of any Exchange Securities for a
period of not less than 180 days after the consummation of the Exchange Offer.

          If, upon consummation of the Exchange Offer, any Purchaser holds
Initial Securities acquired by it as part of its initial distribution, the
Company, simultaneously with the delivery of the Exchange Securities pursuant to
the Exchange Offer, shall cause the Pass Through Trustee to issue and deliver to
such Purchaser upon the written request of such Purchaser, in exchange (the
"Private Exchange") for the Initial Securities held by such Purchaser, a like
-----------------
principal amount of pass-through certificates issued under the Pass Through
Trust Agreements and in all material respects identical to the Initial
Securities (the "Private Exchange Securities").  The Initial Securities, the
                 ---------------------------
Exchange Securities and the Private Exchange Securities are herein collectively
called the "Securities".
            ----------

          In connection with the Exchange Offer, the Company shall:

          (a) mail to each Holder a copy of the prospectus forming part of the
Exchange Offer Registration Statement, together with an appropriate letter of
transmittal and related documents;

          (b) keep the Exchange Offer open for not less than 30 days (or longer,
if required by applicable law) after the date notice thereof is mailed to the
Holders;

          (c) utilize the services of a depositary for the Exchange Offer with
an address in the Borough of Manhattan, The City of New York, which may be the
Pass Through Trustee or an affiliate of the Pass Through Trustee;

                                       3
<PAGE>

          (d) permit Holders to withdraw tendered Transfer Restricted Securities
at any time prior to the close of business, New York time, on the last business
day on which the Exchange Offer shall remain open; and

          (e) otherwise comply with all applicable laws.

     As soon as practicable after the close of the Exchange Offer or the Private
Exchange, as the case may be, the Company shall:

          (x) accept for exchange all the Transfer Restricted Securities validly
tendered and not withdrawn pursuant to the Exchange Offer in accordance with the
Exchange Offer Registration Statement and the letter of transmittal which shall
be an exhibit thereto and the Private Exchange;

          (y) deliver to the Pass Through Trustee for cancellation all the
Initial Securities so accepted for exchange; and

          (z) cause the Pass Through Trustee to issue, authenticate and deliver
promptly to each Holder of the Initial Securities, Exchange Securities or
Private Exchange Securities, as the case may be, equal in principal amount to
the Initial Securities of such Holder so accepted for exchange.

          The Exchange Securities will not be subject to the transfer
restrictions, and the Pass Through Trust Agreements shall provide that all the
Securities will vote and consent together on all matters as one class and none
of the Securities will have the right to vote or consent as a class separate
from one another on any matter.

          Interest on each Exchange Security and Private Exchange Security
issued pursuant to the Exchange Offer and in the Private Exchange will accrue
from the last interest payment date on which interest was paid on the Initial
Securities surrendered in exchange therefor or, if no interest has been paid on
the Initial Securities, from the date of original issue of the Initial
Securities.

          Each Holder participating in the Exchange Offer shall be required to
represent to the Company that at the time of the consummation of the Exchange
Offer (i) any Exchange Securities received by such Holder will be acquired in
the ordinary course of business, (ii) such Holder will have no arrangements or
understanding with any person to participate in the distribution of the
Securities or the Exchange Securities within the meaning of the Securities Act,
(iii) such Holder is not an "affiliate," as defined in Rule 405 of the
Securities Act, of the Company or if it is an affiliate, such Holder will comply
with the registration and prospectus delivery requirements of the Securities Act
to the extent applicable, (iv) if such Holder is not a broker-dealer, that it is
not engaged in, and does not intend to engage in, the distribution of the
Exchange Securities and (v) if such Holder is a broker-dealer, that it will
receive Exchange Securities for its own account in exchange for Initial
Securities that were acquired as a result of market-making

                                       4
<PAGE>

activities or other trading activities and that it will be required to
acknowledge that it will deliver a prospectus in connection with any resale of
such Exchange Securities.

          Notwithstanding any other provisions hereof, the Company will ensure
that (i) any Exchange Offer Registration Statement and any amendment thereto and
any prospectus forming part thereof and any supplement thereto complies in all
material respects with the Securities Act and the rules and regulations
thereunder, (ii) any Exchange Offer Registration Statement and any amendment
thereto does not, when it becomes effective, contain an untrue statement of a
material fact or omit to state a material fact required to be stated therein or
necessary to make the statements therein not misleading and (iii) any prospectus
forming part of any Exchange Offer Registration Statement, and any supplement to
such prospectus, does not include an untrue statement of a material fact or omit
to state a material fact required to be stated therein or necessary in order to
make the statements therein, in the light of the circumstances under which they
were made, not misleading.

          If following the date hereof there has been announced a change in
Commission policy with respect to exchange offers that in the reasonable opinion
of counsel to the Company raises a substantial question as to whether the
Exchange Offer is permitted by applicable federal law, the Company will use its
reasonable best efforts to seek a no-action letter or other favorable decision
from the Commission allowing the Company to consummate the Exchange Offer.

          SECTION 2.  Shelf Registration.  If, (i) because of any change in law
                      ------------------
or in applicable interpretations thereof by the staff of the Commission, the
Company is not permitted to effect an Exchange Offer, as contemplated by Section
1 hereof, (ii) the Exchange Offer is not consummated by the 365th day after the
Funding Date (the "Registration Deadline"), (iii) any Purchaser so requests with
                   ---------------------
respect to the Initial Securities (or the Private Exchange Securities) not
eligible to be exchanged for Exchange Securities in the Exchange Offer and held
by it following consummation of the Exchange Offer or (iv) any Holder (other
than an Exchanging Dealer) is not eligible to participate in the Exchange Offer
or, in the case of any Holder (other than an Exchanging Dealer) that
participates in the Exchange Offer, such Holder does not receive freely
tradeable Exchange Securities on the date of the exchange and any such Holder so
requests, the Company shall take the following actions (the date on which any of
the conditions described in the foregoing clauses (i) through (iv) occur,
including in the case of clauses (iii) or (iv) the receipt of the required
notice, being a "Trigger Date"):
                 ------------

          (a) The Company shall promptly (but in no event more than 45 days
after the Trigger Date (such 45th day being a "Shelf Filing Deadline"), file
                                               ---------------------
with the Commission and thereafter use its reasonable best efforts to cause to
be declared effective no later than 140 days after the Trigger Date, a
registration statement (the "Shelf Registration Statement" and, together with
                             ----------------------------
the Exchange Offer Registration Statement, a "Registration Statement") on an
                                              ----------------------
appropriate form under the Securities Act relating to the offer and sale of the
Transfer Restricted Securities by the Holders thereof from time to time in
accordance with the methods of distribution set forth in the Shelf Registration

                                       5
<PAGE>

Statement and Rule 415 under the Securities Act (hereinafter, the "Shelf
                                                                   -----
Registration"); provided, however, that no Holder (other than a Purchaser) shall
------------    --------  -------
be entitled to have the Securities held by it covered by such Shelf Registration
Statement unless such Holder agrees in writing to be bound by all the provisions
of this Agreement applicable to such Holder.

          (b) The Company shall use its reasonable best efforts to keep the
Shelf Registration Statement continuously effective in order to permit the
prospectus included therein to be lawfully delivered by the Holders of the
relevant Securities, for a period (the "Shelf Registration Period") ending on
the earlier of (A) two years (or such longer period if extended pursuant to
Section 3(j) below) from the date of its effectiveness and (B) the date on which
all the Securities covered by the Shelf Registration Statement (i) have been
sold pursuant thereto or (ii) are no longer restricted securities (as defined in
Rule 144 under the Securities Act, or any successor rule thereof ("Rule 144")).
                                                                   --------
Except during a Suspension Period (as defined herein), the Company shall be
deemed not to have used its reasonable best efforts to keep the Shelf
Registration Statement effective during the requisite period if it voluntarily
takes any action that would result in Holders of Securities covered thereby not
being able to offer and sell such Securities during that period, unless such
action is required by applicable law.

          (c) Notwithstanding any other provisions of this Agreement to the
contrary, the Company shall cause the Shelf Registration Statement and the
related prospectus and any amendment or supplement thereto, as of the effective
date of the Shelf Registration Statement, amendment or supplement, (i) to comply
in all material respects with the applicable requirements of the Securities Act
and the rules and regulations of the Commission and (ii) not to contain any
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary in order to make the statements therein, in light
of the circumstances under which they were made, not misleading, except during a
Suspension Period; provided that clauses (i) and (ii) shall not apply to any
                   --------
untrue statement or omission made in reliance upon and in conformity with
written information furnished to the Company by the Purchasers or Holders
expressly for use therein.

          SECTION 3.  Registration Procedures.  In connection with any Shelf
                      -----------------------
Registration contemplated by Section 2 hereof and, to the extent applicable, any
Exchange Offer contemplated by Section 1 hereof, the following provisions shall
apply:

          (a) The Company shall (i) furnish to each Purchaser, prior to the
filing thereof with the Commission, a copy of the Registration Statement and
each amendment thereof and each supplement, if any, to the prospectus included
therein and, in the event that a Purchaser (with respect to any portion of an
unsold allotment from the original offering) is participating in the Exchange
Offer or the Shelf Registration Statement, the Company shall use its reasonable
best efforts to reflect in each such document, when so filed with the
Commission, such comments as such Purchaser reasonably may propose; (ii) include
the information set forth in Annex A hereto on the cover, in Annex B hereto in
the "Exchange Offer Procedures" section and the "Purpose of the Exchange Offer"
section and in Annex C hereto in the "Plan of Distribution" section of the
prospectus

                                       6
<PAGE>

forming a part of the Exchange Offer Registration Statement and include the
information set forth in Annex D hereto in the Letter of Transmittal delivered
pursuant to the Exchange Offer; (iii) if requested by a Purchaser, include the
information required by Items 507 or 508 of Regulation S-K under the Securities
Act, as applicable, in the prospectus forming a part of the Exchange Offer
Registration Statement; (iv) include within the prospectus contained in the
Exchange Offer Registration Statement a section entitled "Plan of Distribution,"
which, in the reasonable judgment of the Purchasers based upon advise of counsel
(which may be in-house counsel), contains all information required under
applicable securities laws, including, without limitation, a summary statement
of the positions taken or policies made by the staff of the Commission with
respect to the potential "underwriter" status of any broker-dealer that is the
beneficial owner (as defined in Rule 13d-3 under the Securities Exchange Act of
1934, as amended, and the rules and regulations of the Commission promulgated
thereunder (the "Exchange Act")) of Exchange Securities received by such broker-
                 ------------
dealer in the Exchange Offer (a "Participating Broker-Dealer"); and (v) in the
                                 ---------------------------
case of a Shelf Registration Statement include the names of the Holders who
propose to sell Securities pursuant to the Shelf Registration Statement as
selling securityholders.

          (b)  The Company shall give written notice to the Purchasers, the
Holders of the Securities and any Participating Broker-Dealer from whom the
Company has received prior written notice that it will be a Participating
Broker-Dealer in the Exchange Offer (which notice pursuant to clauses (ii)-(v)
hereof shall be accompanied by an instruction to suspend the use of the
prospectus until the requisite changes have been made):

               (i)   when the Registration Statement or any amendment thereto
          has been filed with the Commission and when the Registration Statement
          or any post-effective amendment thereto has become effective;

               (ii)  of any request by the Commission for amendments or
          supplements to the Registration Statement or the prospectus included
          therein or for additional information;

               (iii) of the issuance by the Commission of any stop order
          suspending the effectiveness of the Registration Statement or the
          initiation of any proceedings for that purpose;

               (iv)  of the receipt by the Company or its legal counsel of any
          notification with respect to the suspension of the qualification of
          the Securities for sale in any jurisdiction or the initiation or
          threatening of any proceeding for such purpose; and

               (v) of the happening of any event that requires the Company to
          make changes in the Registration Statement or the prospectus in order
          that the Registration Statement or the prospectus do not contain an
          untrue statement of a material fact nor omit to state a material fact
          required to be

                                       7
<PAGE>

          stated therein or necessary to make the statements therein (in the
          case of the prospectus, in light of the circumstances under which they
          were made) not misleading.

          (c) The Company shall make every reasonable effort to obtain the
withdrawal at the earliest possible time, of any order suspending the
effectiveness of the Registration Statement.

          (d) If any Holder of Securities included within the coverage of the
Shelf Registration shall so request in writing, the Company shall furnish to
each such Holder, without charge, at least one conformed copy of the Shelf
Registration Statement and any post-effective amendment thereto, including
financial statements and schedules, and, if the Holder so reasonably requests in
writing, all exhibits thereto (including those, if any, incorporated by
reference).

          (e) The Company shall deliver to each Exchanging Dealer and each
Purchaser, and to any other Holder who so requests in writing, without charge,
at least one copy of the Exchange Offer Registration Statement and any post-
effective amendment thereto, including financial statements and schedules, and,
if any Purchaser or any such Holder reasonably requests in writing, all exhibits
thereto (including those incorporated by reference).

          (f) The Company shall, during the Shelf Registration Period (except
during a Suspension Period), deliver to each Holder of Securities included
within the coverage of the Shelf Registration, without charge, as many copies of
the prospectus (including each preliminary prospectus) included in the Shelf
Registration Statement and any amendment or supplement thereto as such person
may reasonably request.  The Company consents, subject to the provisions of this
Agreement, to the use of the prospectus forming a part of the Shelf Registration
Statement or any amendment or supplement thereto by each of the selling Holders
of the Securities in connection with the offering and sale of the Securities
covered by the prospectus, or any amendment or supplement thereto, included in
the Shelf Registration Statement.

          (g) The Company shall deliver to each Purchaser, any Exchanging
Dealer, any Participating Broker-Dealer and such other persons required to
deliver a prospectus following the Exchange Offer, without charge, as many
copies of the final prospectus included in the Exchange Offer Registration
Statement and any amendment or supplement thereto as such persons may reasonably
request.  The Company consents, subject to the provisions of this Agreement, to
the use of the prospectus forming a part of the Exchange Offer Registration
Statement or any amendment or supplement thereto by any Purchaser, if necessary,
any Participating Broker-Dealer and such other persons required to deliver a
prospectus following the Exchange Offer in connection with the offering and sale
of the Exchange Securities covered by the prospectus, or any amendment or
supplement thereto, included in such Exchange Offer Registration Statement,
except during a Suspension Period.

                                       8
<PAGE>

          (h) Prior to any public offering of the Securities pursuant to any
Registration Statement the Company shall use its reasonable best efforts to
register or qualify or cooperate with the Holders of the Securities included
therein and their respective counsel in connection with the registration or
qualification of the Securities for offer and sale under the securities or "blue
sky" laws of such states of the United States as any Holder of the Securities
reasonably requests in writing and do any and all other acts or things necessary
or advisable to enable the offer and sale in such jurisdictions of the
Securities covered by such Registration Statement; provided, however, that the
                                                   --------  -------
Company shall not be required to (i) qualify generally to do business in any
jurisdiction where it is not then so qualified or (ii) take any action which
would subject it to general service of process or to taxation in any
jurisdiction where it is not then so subject.

          (i) The Company shall cooperate with the Holders of the Securities to
facilitate the timely preparation and delivery of certificates representing the
Securities to be sold pursuant to any Registration Statement free of any
restrictive legends and in such denominations and registered in such names as
the Holders may request a reasonable period of time prior to sales of the
Securities pursuant to such Registration Statement.

          (j) Upon the occurrence of any event contemplated by paragraphs (ii)
through (v) of Section 3(b) above during the period for which the Company is
required to maintain an effective Registration Statement, the Company shall
promptly prepare and file a post-effective amendment to the Registration
Statement or a supplement to the related prospectus and any other required
document so that, as thereafter delivered to Holders of the Securities or
purchasers of Securities, the prospectus will not contain an untrue statement of
a material fact or omit to state any material fact required to be stated therein
or necessary to make the statements therein, in light of the circumstances under
which they were made, not misleading.  If the Company notifies the Purchasers,
the Holders of the Securities and any known Participating Broker-Dealer in
accordance with paragraphs (ii) through (v) of Section 3(b) above to suspend the
use of the prospectus (and any exchange or sales) until the requisite changes to
the prospectus have been made, then the Purchasers, the Holders of the
Securities and any such Participating Broker-Dealers shall suspend use of such
prospectus (and any exchange or sales) until receipt of the amendment,
supplement or other document contemplated hereunder, and the period of
effectiveness of the Shelf Registration Statement provided for in Section 2(b)
above and the Exchange Offer Registration Statement provided for in Section 1
above shall each be extended by the number of days from and including the date
of the giving of such notice to and including the date when the Purchasers, the
Holders of the Securities and any known Participating Broker-Dealer shall have
received such amended or supplemented prospectus pursuant to this Section 3(j).

          (k) Not later than the effective date of the applicable Registration
Statement, the Company will provide a CUSIP number for the Initial Securities,
the Exchange Securities or the Private Exchange Securities, as the case may be,
and provide the applicable trustee with printed certificates for the Initial
Securities, the Exchange

                                       9
<PAGE>

Securities or the Private Exchange Securities, as the case may be, in a
form eligible for deposit with The Depository Trust Company.

          (l) The Company will comply with all rules and regulations of the
Commission to the extent and so long as they are applicable to the Exchange
Offer or the Shelf Registration and will make generally available to its
security holders (or otherwise provide in accordance with Section 11(a) of the
Securities Act) an earnings statement satisfying the provisions of Section 11(a)
of the Securities Act, no later than 45 days after the end of a 12-month period
(or 90 days, if such period is a fiscal year) beginning with the first month of
the Company's first fiscal quarter commencing after the effective date of the
Registration Statement, which statement shall cover such 12-month period.

          (m) The Company shall cause the Pass Through Trust Agreements to be
qualified under the Trust Indenture Act of 1939, as amended, and the rules and
regulations of the Commission promulgated thereunder (the "TIA") in a timely
                                                           ---
manner, and in no event later than the effective date of the applicable
Registration Statement, as required by applicable law.

          (n) The Company may require each Holder of Securities to be registered
pursuant to the Shelf Registration Statement to furnish to the Company such
information regarding the Holder and the distribution of the Securities as the
Company may from time to time reasonably require for inclusion in the Shelf
Registration Statement, and the Company may exclude from such registration the
Securities of any Holder that unreasonably fails to furnish such information
within a reasonable time after receiving such request.

          (o) The Company shall enter into such customary agreements (including,
if requested, an underwriting agreement in form consistent with the Purchase
Agreement) and take all such other customary and appropriate action, if any, as
any Holder of the Securities shall reasonably request in order to facilitate the
disposition of the Securities pursuant to any Shelf Registration.

          (p) In the case of any Shelf Registration, the Company shall (i) make
reasonably available for inspection by the Holders of the Securities, any
underwriter participating in any disposition pursuant to the Shelf Registration
Statement and any attorney, accountant or other agent retained by the Holders of
the Securities or any such underwriter all relevant financial and other records,
pertinent corporate documents and properties of the Company and (ii) use its
reasonable efforts to cause the Company's officers, directors, employees,
accountants and counsel to supply all relevant information reasonably requested
by the Holders of the Securities or any such underwriter, attorney, accountant
or agent in connection with the Shelf Registration Statement, in each case, as
shall be reasonably necessary to enable such persons, to conduct a reasonable
investigation within the meaning of Section 11 of the Securities Act; provided,
                                                                      --------
however, that such persons shall first agree in writing with the Company that,
-------
for a period of one year from the receipt of such information, any information
that is reasonably and in good faith designated by the Company in writing as
confidential at the time of delivery of such

                                       10
<PAGE>

information shall be kept confidential by such persons, unless (i) disclosure of
such information is required by court or administrative order or is necessary to
respond to inquiries by regulatory authorities, (ii) disclosure of such
information is required by law (including any disclosure requirements pursuant
to federal securities laws in connection with the filing of the Shelf
Registration or the use of any prospectus), (iii) such information becomes
available to such persons from a source other than the Company and its
subsidiaries and such source is not known by such persons to be bound by a
confidentiality agreement; provided, further, that the foregoing inspection and
                           --------  -------
information gathering shall be coordinated on behalf of the Purchasers by you
and on behalf of the other parties, by one counsel designated by and on behalf
of such other parties as described in Section 4 hereof, provided, however, that
                                                        --------  -------
such counsel shall be Shearman & Sterling, or such other counsel as is
reasonably acceptable to the Company (the "Special Counsel").
                                           ---------------

          (q) In the case of any Shelf Registration, the Company, if requested
by the Holders of at least 5% of the aggregate principal amount of the
outstanding Securities, shall (or in the case of an underwritten offering, shall
use its best efforts to) cause (i) its counsel to deliver an opinion and updates
thereof relating to the Securities in customary form addressed to such Holders
and the managing underwriters, if any, thereof; (ii) its officers to execute and
deliver all customary documents and certificates and updates thereof reasonably
requested by any underwriters of the applicable Securities; and (iii) its
independent public accountants and the independent public accountants with
respect to any other entity for which financial information is provided in the
Shelf Registration Statement to provide to the selling Holders of the applicable
Securities and any underwriter therefor a comfort letter in customary form and
covering matters of the type customarily covered in comfort letters in
connection with primary underwritten offerings, subject to receipt of
appropriate documentation as contemplated, and only if permitted, by Statement
of Auditing Standards No. 72.

          (r) If an Exchange Offer or a Private Exchange is to be consummated,
upon delivery of the Initial Securities by Holders to the Company (or to such
other Person as directed by the Company) in exchange for the Exchange Securities
or the Private Exchange Securities, as the case may be, the Company shall mark,
or caused to be marked, on the Initial Securities so exchanged that such Initial
Securities are being canceled in exchange for the Exchange Securities or the
Private Exchange Securities, as the case may be; in no event shall the Initial
Securities be marked as paid or otherwise satisfied.

          (s) The Company will use its reasonable best efforts to (a) if the
Initial Securities have been rated prior to the initial sale of such Initial
Securities, confirm such ratings will apply to the Securities covered by a
Registration Statement, or (b) if the Initial Securities were not previously
rated, cause the Securities covered by a Registration Statement to be rated with
the appropriate rating agencies, if so requested by Holders of a majority in
aggregate principal amount of Securities covered by such Registration Statement,
or by the managing underwriters, if any.

                                       11
<PAGE>

          (t) In the event that any broker-dealer registered under the Exchange
Act shall underwrite any Securities or participate as a member of an
underwriting syndicate or selling group or "assist in the distribution" (within
the meaning of the Conduct Rules (the "Rules") of the National Association of
                                       -----
Securities Dealers, Inc. ("NASD")) thereof, whether as a Holder of such
                           ----
Securities or as an underwriter, a placement or sales agent or a broker or
dealer in respect thereof, or otherwise, the Company will assist such broker-
dealer in complying with the requirements of such Rules, including, without
limitation, by (i) if such Rules, including Rule 2720, shall so require,
engaging a "qualified independent underwriter" (as defined in Rule 2720) to
participate in the preparation of the Registration Statement relating to such
Securities, to exercise usual standards of due diligence in respect thereto and,
if any portion of the offering contemplated by such Registration Statement is an
underwritten offering or is made through a placement or sales agent, to
recommend the yield of such Securities, (ii) indemnifying any such qualified
independent underwriter to the extent of the indemnification of underwriters
provided in Section 5 hereof and (iii) providing such information to such
broker-dealer as may be required in order for such broker-dealer to comply with
the requirements of the Rules.

          (u) The Company shall use its reasonable best efforts to take all
other steps necessary to effect the registration of the Securities covered by a
Registration Statement contemplated hereby.

          SECTION 4. Registration Expenses. All expenses incident to the
                     ---------------------
Company's performance of and compliance with this Agreement will be borne by the
Company, regardless of whether a Registration Statement is ever filed or becomes
effective, including without limitation;

               (i)   all registration and filing fees and expenses;

               (ii)  all fees and expenses of compliance with federal securities
          and state "blue sky" or securities laws;

               (iii) all expenses of printing (including printing certificates
          for the Securities to be issued in the Exchange Offer and the Private
          Exchange and printing of Prospectuses), messenger and delivery
          services and telephone;

               (iv)  all fees and disbursements of counsels for the Company and
          the Pass Through Trustee;

               (v)   all application and filing fees in connection with listing
          the Exchange Securities on a national securities exchange or automated
          quotation system pursuant to the requirements hereof; and

                                       12
<PAGE>

               (vi) all fees and disbursements of independent certified public
          accountants of the Company (including the expenses of any special
          audit and comfort letters required by or incident to such
          performance).

The Company will bear its internal expenses (including, without limitation, all
salaries and expenses of its officers and employees performing legal or
accounting duties), the expenses of any annual audit and the fees and expenses
of any person, including special experts, retained by the Company.

          (a) In connection with any Registration Statement required by this
Agreement, the Company will reimburse the Purchasers and the holders of Transfer
Restricted Securities who are tendering Initial Securities in the Exchange Offer
and/or selling or reselling Securities pursuant to the "Plan of Distribution"
contained in the Exchange Offer Registration Statement or the Shelf Registration
Statement, as applicable, for the reasonable fees and disbursements, not to
exceed $25,000 in the aggregate, of not more than one counsel, chosen by the
holders of a majority in principal amount of the Securities for whose benefit
such Registration Statement is being prepared; provided, however, that such
                                               --------  -------
counsel shall be the Special Counsel.  Each Holder shall pay all underwriting
discounts, commissions and transfer taxes, if any, relating to the sale or
disposition of such Holder's Securities pursuant to the Shelf Registration.

          SECTION 5. Indemnification. The Company agrees to indemnify and hold
                     ---------------
harmless each Holder of the Securities, any Participating Broker-Dealer and each
person, if any, who controls each Holder or such Participating Broker-Dealer
within the meaning of the Securities Act (each Holder, any Participating Broker-
Dealer and such controlling persons are referred to collectively as the
"Indemnified Parties") against any and all losses, claims, damages or
 -------------------
liabilities, joint or several, to which they or any of them may become subject
under the Securities Act or otherwise, and to reimburse the Indemnified Parties
for any legal or other expenses incurred by them in connection with
investigating or defending any actions, insofar as such losses, claims, damages,
liabilities or actions arise out of or are based upon any untrue statement or
alleged untrue statement of a material fact contained in a Registration
Statement or prospectus or in any amendment or supplement thereto or in any
preliminary prospectus relating to a Shelf Registration, or arise out of or are
based upon any omission or alleged omission to state therein a material fact
required to be stated therein or necessary to make the statements therein, in
light of the circumstances under which they were made, not misleading, except
insofar as such losses, claims, damages, liabilities or actions arise out of or
are based upon any such untrue statement or omission or alleged untrue statement
or omission which was made in a Registration Statement or prospectus or in any
amendment or supplement thereto or in any preliminary prospectus relating to a
Shelf Registration in reliance upon and in conformity with information furnished
in writing to the Company by, or through such Indemnified Party or on behalf of
such Indemnified Party for use therein and except that this indemnity shall not
inure to the benefit of any Holder or Participating Broker-Dealer from whom the
person asserting any such losses, claims, damages or liabilities purchased the
Securities concerned, to the
                                       13
<PAGE>

extent that a prospectus or supplement to such prospectus relating to such
Securities was required to be delivered by such Holder or Participating Broker-
Dealer under the Securities Act in connection with such purchase and any such
loss, claim, damage or liability of such Holder or Participating Broker-Dealer
results from the fact that there was not sent or given to such person, at or
prior to the written confirmation of the sale of such Securities to such person,
a copy of the final prospectus or supplement to such prospectus if the Company
had previously furnished copies thereof to such Holder or Participating Broker-
Dealer.

          (a) Each Holder of the Securities, severally and not jointly, will
indemnify and hold harmless the Company and each person, if any, who controls
the Company within the meaning of the Securities Act or the Exchange Act from
and against any losses, claims, damages or liabilities or any actions in respect
thereof, to which the Company or any such controlling person may become subject
under the Securities Act, the Exchange Act or otherwise, insofar as such losses,
claims, damages, liabilities or actions arise out of or are based upon any
untrue statement or alleged untrue statement of a material fact contained in a
Registration Statement or prospectus or in any amendment or supplement thereto
or in any preliminary prospectus relating to a Shelf Registration, or arise out
of or are based upon the omission or alleged omission to state therein a
material fact necessary to make the statements therein not misleading, but in
each case only to the extent that the untrue statement or omission or alleged
untrue statement or omission was made in reliance upon and in conformity with
written information pertaining to such Holder and furnished to the Company by or
on behalf of such Holder specifically for inclusion therein; and, subject to the
limitation set forth immediately preceding this clause, shall reimburse, as
incurred, the Company for any legal or other expenses reasonably incurred by the
Company or any such controlling person in connection with investigating or
defending any loss, claim, damage, liability or action in respect thereof.

          (b) Promptly after receipt by a party indemnified under Section 5(a)
or Section 5(b) above of written notice of any loss, claim, damage or liability
in respect of which indemnity may be sought by it hereunder, such indemnified
party will, if a claim is to be made against an indemnifying party, notify the
indemnifying party thereof in writing, but the omission so to notify the
indemnifying party will not relieve the indemnifying party from any liability
(otherwise than under Section 5(a) or Section 5(b) hereof) which it may have to
the indemnified party.  Thereafter, the indemnified party and the indemnifying
party shall consult, to the extent appropriate, with a view to minimizing the
cost to the indemnifying party of its obligations hereunder.  In case any
indemnified party receives written notice of any loss, claim, damage or
liability in respect of which indemnity may be sought by it hereunder and it
notifies the indemnifying party thereof, the indemnifying party will be entitled
to participate therein, and to the extent that it may elect by written notice
delivered to the indemnified party promptly after receiving the aforesaid notice
from the indemnified party, to assume the defense thereof with counsel
reasonably satisfactory to the indemnified party; provided, however, that if the
                                                  --------  -------
parties against which any loss, claim, damage or liability arises include both
the indemnified party and the indemnifying party and the indemnified party shall
have reasonably concluded that defenses available to it create a conflict of
interest for the counsel selected

                                       14
<PAGE>

by the indemnifying party under the code of professional responsibility
applicable to such counsel, the indemnified party shall have the right to select
one separate counsel to assume such legal defenses and otherwise to participate
in the defenses of such loss, claim, damage or liability on behalf of the
indemnified party. Upon receipt by the indemnified party of notice from the
indemnifying party of its selection so to assume the defense of such loss,
claim, damage or liability and approval by the indemnified party of counsel, the
indemnifying party shall not be liable to the indemnified party under Section
5(a) or Section 5(b) hereof for any legal or other expenses subsequently
incurred by the indemnified party in connection with the defense thereof unless
(i) the indemnified party shall have employed such counsel in connection with
the assumption of legal defenses in accordance with the proviso to the next
preceding sentence, (ii) the indemnifying party shall not have employed and
continued to employ counsel reasonably satisfactory to the indemnified party to
represent the indemnified party within a reasonable time after notice of
commencement of the action or (iii) the indemnifying party shall have authorized
in writing the employment of separate counsel for the indemnified party at the
expense of the indemnifying party. No indemnifying party shall, without prior
written consent of the indemnified party, effect any settlement of any pending
or threatened action in respect of which the indemnified party is or is entitled
or subject to be a party and the indemnified party is entitled to indemnity
hereunder unless such settlement includes an unconditional release of the
indemnified party from all liability on any claims that are the subject matter
of such action and does not include a statement as to or an admission of fault,
culpability or a failure to act by or on behalf of any indemnified party. No
indemnifying party shall be liable for any settlement, compromise or consent to
the entry of any order adjudicating or otherwise disposing of any loss, claim,
damage or liability effected without its consent.

          (c) The agreements contained in this Section 5 shall survive the sale
of the Securities pursuant to a Registration Statement and shall remain in full
force and effect, regardless of any termination or cancellation of this
Agreement (including, without limitation, pursuant to Section 9(l) hereto) or
any investigation made by or on behalf of any indemnified party.

          SECTION 6.  Additional Interest Under Certain Circumstances.  (a)
                      -----------------------------------------------
Additional interest (the "Additional Interest") with respect to the Securities
                          -------------------
shall be assessed as follows if any of the following events occur (each such
event in clauses (i) through (ii) below being herein called a "Registration
                                                               ------------
Default"):
-------

               (i)  (A) the Exchange Offer has not been consummated on or prior
          to the Registration Deadline and (B) the Shelf Registration Statement
          required by this Agreement is not declared effective by the Commission
          on or prior to the Registration Deadline; or

               (ii) the Shelf Registration Statement required by this Agreement
          has been declared effective by the Commission but (A) such Shelf
          Registration Statement thereafter ceases to be effective at any time
          that the Company is obligated hereby to maintain the effectiveness
          thereof or (B) such Shelf Registration Statement or the related
          prospectus ceases

                                       15
<PAGE>

          to be usable in connection with resales of Transfer Restricted
          Securities during the periods specified herein because either (1) any
          event occurs as a result of which the related prospectus forming part
          of such Shelf Registration Statement would include any untrue
          statement of a material fact or omit to state any material fact
          necessary to make the statements therein in the light of the
          circumstances under which they were made not misleading, or (2) it
          shall be necessary to amend such Shelf Registration Statement or
          supplement the related prospectus, to comply with the Securities Act
          or the Exchange Act or the respective rules thereunder.

          Additional Interest shall accrue on the Securities over and above the
interest set forth in the title of the Securities from and including the date on
which any such Registration Default shall occur to but excluding the date on
which all such Registration Defaults have been cured, at a rate of 0.50% per
annum (the "Additional Interest Rate"), which Additional Interest Rate shall be
            ------------------------
the same regardless of whether one or more such Registration Defaults shall be
continuing simultaneously.  Following the cure of all Registration Defaults, the
accrual of Additional Interest will cease and the interest rate on the
Securities will be reduced to the interest rate it would have been had no such
Registration Default occurred.

          (b) A Registration Default referred to in Section 6(a)(ii) hereof
shall be deemed not to have occurred and be continuing in relation to a Shelf
Registration Statement or the related prospectus if such Registration Default
has occurred solely as a result of (i) the filing of a post-effective amendment
to such Shelf Registration Statement to incorporate annual audited financial
information with respect to the Company where such post-effective amendment is
not yet effective and needs to be declared effective to permit Holders to use
the related prospectus or (ii) the occurrence of other material events or
developments with respect to the Company that would need to be described in such
Shelf Registration Statement or the related prospectus, provided that, during
                                                        --------
the Suspension Period, the Company is proceeding promptly and in good faith to
amend or supplement such Shelf Registration Statement and related prospectus to
describe such events.  For purposes hereof, the "Suspension Period" shall mean
                                                 -----------------
the period of time commencing on and including the date that the Company gives
notice that the Shelf Registration Statement is no longer effective or the
prospectus included therein is no longer usable as a result of the occurrence of
such events or developments, and ending on the earliest to occur of (x) the date
on which each seller of Securities covered by the Shelf Registration Statement
either receives copies of the supplemented or amended prospectus contemplated
herein or is advised in writing by the Company that the use of the prospectus
may be resumed, (y) the expiration of 45 consecutive calendar days during which
such Suspension Period has been in effect, and (z) the expiration of an
aggregate of 60 days in any consecutive twelve-month period during which one or
more Suspension Periods has been in effect.  Additional Interest shall be
payable in accordance with the above paragraph from and excluding the last day
of a Suspension Period until such Registration Default is cured.

                                       16
<PAGE>

          (c) Any amounts of Additional Interest due pursuant to Section 6(a)
will be payable in cash on the regular interest payment dates with respect to
the Securities. The amount of Additional Interest will be determined by
multiplying the applicable Additional Interest Rate by the principal amount of
the Securities and further multiplied by a fraction, the numerator of which is
the number of days such Additional Interest Rate was applicable during such
period (determined on the basis of a 360-day year comprised of twelve 30-day
months), and the denominator of which is 360.

          (d) "Transfer Restricted Securities" means each Security until (i) the
               ------------------------------
date on which such Security has been exchanged by a person other than a broker-
dealer for a freely transferable Exchange Security in the Registered Exchange
Offer, (ii) following the exchange by a broker-dealer in the Registered Exchange
Offer of an Initial Security for an Exchange Note, the date on which such
Exchange Note is sold to a purchaser who receives from such broker-dealer on or
prior to the date of such sale a copy of the prospectus contained in the
Exchange Offer Registration Statement, (iii) the date on which such Security has
been effectively registered under the Securities Act and disposed of in
accordance with the Shelf Registration Statement or (iv) the date on which such
Security is distributed to the public pursuant to Rule 144 under the Securities
Act or is saleable pursuant to Rule 144(k) under the Securities Act.

          (e) The parties hereto agree that the additional interest provided for
in this Section 6 constitutes a reasonable estimate of and is intended to
constitute the sole remedy to Holders of Securities by reason of the failure of
the Shelf Registration Statement or the Exchange Offer Registration Statement to
be declared effective and the Registered Exchange Offer to be consummated, in
each case to the extent required by this Agreement.

          SECTION 7.  Rules 144 and 144A.  The Company shall use its reasonable
                      ------------------
best efforts to file the reports required to be filed by it under the Securities
Act and the Exchange Act in a timely manner and, if at any time the Company is
not required to file such reports, it will, upon the request of any Holder of
Securities, make publicly available other information so long as necessary to
permit sales of their securities pursuant to Rules 144 and 144A.  The Company
covenants that it will take such further action as any Holder of Securities may
reasonably request, all to the extent required from time to time to enable such
Holder to sell Securities without registration under the Securities Act within
the limitation of the exemptions provided by Rules 144 and 144A (including the
requirements of Rule 144A(d)(4)).  The Company will provide a copy of this
Agreement to prospective purchasers of Initial Securities identified to the
Company by the Initial Purchasers upon request.  Upon the request of any Holder
of Initial Securities, the Company shall deliver to such Holder a written
statement as to whether it has complied with such requirements.  Notwithstanding
the foregoing, nothing in this Section 7 shall be deemed to require the Company
to register any of its securities pursuant to the Exchange Act.

          SECTION 8.  Underwritten Registrations.  If any of the Transfer
                      --------------------------
Restricted Securities covered by any Shelf Registration are to be sold in an
Underwritten

                                       17
<PAGE>

Offering, the investment banker or investment bankers and manager or managers
that will administer the offering ("Managing Underwriters") will be selected by
                                    ---------------------
the Holders of a majority in aggregate principal amount of such Transfer
Restricted Securities to be included in such offering, subject to the consent of
the Company (which shall not be unreasonably withheld or delayed), and such
Holders shall be responsible for all underwriting commissions and discounts in
connection therewith.

          No person may participate in any underwritten registration hereunder
unless such person (i) agrees to sell such person's Transfer Restricted
Securities on the basis reasonably provided in any underwriting arrangements
approved by the persons entitled hereunder to approve such arrangements and (ii)
completes and executes all questionnaires, powers of attorney, indemnities,
underwriting agreements and other documents reasonably required under the terms
of such underwriting arrangements.

          SECTION 9.  Miscellaneous.  (a)  No Inconsistent Agreements.  The
                      -------------        --------------------------
Company will not on or after the date of this Agreement enter into any agreement
with respect to its securities that is inconsistent with the rights granted to
the Holders in this Agreement or otherwise conflicts with the provisions hereof.
The rights granted to the Holders hereunder do not in any way conflict with and
are not inconsistent with the rights granted to the holders of the Company's
securities under any agreement in effect on the date hereof.

          (b) Amendments and Waivers.  The provisions of this Agreement may not
              ----------------------
be amended, modified or supplemented, and waivers or consents to departures from
the provisions hereof may not be given, except by the Company and the written
consent of the Holders of a majority in principal amount of the Securities
affected by such amendment, modification, supplement, waiver or consents, or as
otherwise provided in the Pass Through Trust Agreements.

          (c) Notices.  All notices and other communications provided for or
              -------
permitted hereunder shall be made in writing by hand delivery, first-class mail,
facsimile transmission, or air courier which guarantees overnight delivery:

          (1) if to a Holder of the Securities, at the most current address
     given by such Holder to the Company.

          (2) if to the Purchasers:

               Credit Suisse First Boston Corporation
               Eleven Madison Avenue
               New York, NY 10010-3629
               Fax No.:  (212) 325-8278
               Attention:  Transactions Advisory Group

     with a copy to:

                                       18
<PAGE>


               Shearman & Sterling
               599 Lexington Avenue
               New York, NY  10022-6069
               Fax No.: (212) 848-7179
               Attention:  Alexander C. Bancroft, Esq.

          (3)  if to the Company, at its address as follows:

               Southern Energy Mid-Atlantic, LLC
               1155 Perimeter Center West
               Atlanta, Georgia  30338
               Fax:  (678) 579-5001
               Attention:  President

     with a copy to:

               Troutman Sanders LLP
               Bank of America Plaza, Suite 5200
               600 Peachtree Street, N.E.
               Atlanta, Georgia  30308
               Fax:  (404) 885-3001
               Attention:  John T.W. Mercer, Esq.

          All such notices and communications shall be deemed to have been duly
given:  at the time delivered by hand, if personally delivered; three business
days after being deposited in the mail, postage prepaid, if mailed; when receipt
is acknowledged by recipient's facsimile machine operator, if sent by facsimile
transmission; and on the day delivered, if sent by overnight air courier
guaranteeing next day delivery.

          (d) Third Party Beneficiaries.  The Holders shall be third party
              -------------------------
beneficiaries to the agreements made hereunder between the Company, on the one
hand, and the  Purchasers, on the other hand, and shall have the right to
enforce such agreements directly to the extent they may deem such enforcement
necessary or advisable to protect their rights or the rights of Holders
hereunder.

          (e) Successors and Assigns.  This Agreement shall be binding upon the
              ----------------------
Company and its successors and assigns.  If any transferee of any Purchaser
shall acquire a Security in any manner, whether by operation of law or
otherwise, by taking and holding such Security, such person shall be
conclusively deemed to have agreed to be bound by and to perform all the terms
and provisions of this Agreement and such person shall be entitled to receive
the benefits hereof.

          (f) Counterparts.  This Agreement may be executed in any number of
              ------------
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be an original and all of which taken
together shall constitute one and the same agreement.

                                       19
<PAGE>

          (g) Headings.  The headings in this Agreement are for convenience of
              --------
reference only and shall not limit or otherwise affect the meaning hereof.

          (h) Governing Law.  THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED
              -------------
IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK WITHOUT REGARD TO
PRINCIPLES OF CONFLICTS OF LAWS.

          (i) Severability.  If any one or more of the provisions contained
              ------------
herein, or the application thereof in any circumstance, is held invalid, illegal
or unenforceable, the validity, legality and enforceability of any such
provision in every other respect and of the remaining provisions contained
herein shall not be affected or impaired thereby.

          (j) Securities Held by the Company.  Whenever the consent or approval
              ------------------------------
of Holders of a specified percentage of principal amount of Securities is
required hereunder, Securities held by the Company or its affiliates (other than
subsequent Holders of Securities if such subsequent Holders are deemed to be
affiliates solely by reason of their holdings of such Securities) shall not be
counted in determining whether such consent or approval was given by the Holders
of such required percentage.

          (k) Agent for Service; Submission to Jurisdiction; Waiver of
              --------------------------------------------------------
Immunities.  By the execution and delivery of this Agreement, the Company (i)
----------
acknowledges that it has, by separate written instrument, irrevocably designated
and appointed CT Corporation System (and any successor entity), as its
authorized agent upon which process may be served in any suit or proceeding
arising out of or relating to this Agreement that may be instituted in any
federal or state court in the State of New York or brought under federal or
state securities laws, and acknowledges that CT Corporation System has accepted
such designation, (ii) submits to the nonexclusive jurisdiction of any such
court in any such suit or proceeding, and (iii) agrees that service of process
upon CT Corporation System and written notice of said service to the Company
shall be deemed in every respect effective service of process upon the Company
in any such suit or proceeding.  The Company further agrees to take any and all
action, including the execution and filing of any and all such documents and
instruments, as may be necessary to continue such designation and appointment of
CT Corporation System in full force and effect so long as any of the Transfer
Restricted Securities shall be outstanding.  To the extent that the Company may
acquire any immunity from jurisdiction of any court or from any legal process
(whether through service of notice, attachment prior to judgment, attachment in
aid of execution, execution or otherwise) with respect to itself or its
property, it hereby irrevocably waives such immunity in respect of this
Agreement, to the fullest extent permitted by law.

          (l) Termination of Agreement.  This Agreement shall automatically
              ------------------------
terminate upon payment in full of the Initial Securities solely from Escrowed
Funds (as defined in the Pass Through Trust Agreements).  Upon such termination,
neither of the parties hereto shall have any further obligations hereunder;
provided, however, that notwithstanding anything to the contrary in this
--------  -------
agreement, the obligations of the

                                       20
<PAGE>

Company under Section 5 hereto shall not terminate, and shall remain in full
force and effect.

                                       21
<PAGE>

          If the foregoing is in accordance with your understanding of our
agreement, please sign and return to the Company a counterpart hereof, whereupon
this instrument, along with all counterparts, will become a binding agreement
among the several Purchasers, the Company and SEI in accordance with its terms.


                              Very truly yours,

                              SOUTHERN ENERGY MID-ATLANTIC, LLC

                              By: /s/ Raymond V. Haley
                                  ------------------------------
                                  Name: Raymond V. Haley
                                  Title: Vice President

The foregoing Registration Rights Agreement is hereby confirmed and accepted as
of the date first above written.

CREDIT SUISSE FIRST BOSTON CORPORATION
acting on behalf of itself and as representative of the several Purchasers


By: /s/ James Bartlett
    --------------------
    Name: James Bartlett
    Title: Director

                                       22