<PAGE>

                                                                     Exhibit 4.4

This instrument was prepared by,
and when recorded should be
returned to:

Richard W. Astle
Sidley Austin Brown & Wood
Bank One Plaza
10 South Dearborn Street
Chicago, Illinois 60603



                             Supplemental Indenture

                                   __________

                           Dated as of March 14, 2003

                                   __________

                           Commonwealth Edison Company

                                       to

                            BNY Midwest Trust Company

                                       and

                                  D. G. Donovan

             Trustees under Mortgage Dated July 1, 1923, and Certain
                         Indentures Supplemental Thereto


                                   __________


                            Providing for Issuance of


                     FIRST MORTGAGE 4.70% BONDS, SERIES 101
                               DUE APRIL 15, 2015

<PAGE>

This Supplemental Indenture, dated as of March 14, 2003, between Commonwealth
Edison Company, a corporation organized and existing under the laws of the State
of Illinois (hereinafter called the "Company") having an address at 10 South
Dearborn Street, 37th floor, Chicago, Illinois 60603, party of the first part,
and BNY Midwest Trust Company, atrust company organized and existing under the
laws of the State of Illinois having an address at 2 North LaSalle Street, Suite
1020, Chicago, Illinois 60602, and D.G. Donovan, an individual having an address
at 2 North LaSalle Street, Suite 1020, Chicago, Illinois 60602, as Trustee and
Co-Trustee, respectively, under the Mortgage of the Company dated July 1, 1923,
as amended and supplemented by Supplemental Indenture dated August 1, 1944 and
the subsequent supplemental indentures hereinafter mentioned, parties of the
second part (said Trustee being hereinafter called the "Trustee", the Trustee
and said Co-Trustee being hereinafter together called the "Trustees", and said
Mortgage dated July 1, 1923, as amended and supplemented by said Supplemental
Indenture dated August 1, 1944 and subsequent supplemental indentures, being
hereinafter called the "Mortgage"),

                              W I T N E S S E T H:

     WHEREAS, the Company duly executed and delivered the Mortgage to provide
for the issue of, and to secure, its bonds, issuable in series and without limit
as to principal amount except as provided in the Mortgage; and

     WHEREAS, the Company from time to time has executed and delivered
supplemental indentures to the Mortgage to provide for (i) the creation of
additional series of bonds secured by the Mortgage, (ii) the amendment of
certain of the terms and provisions of the Mortgage and (iii) the confirmation
of the lien of the Mortgage upon property of the Company, such supplemental
indentures that are currently effective and the respective dates, parties
thereto and purposes thereof, being as follows:

<TABLE>
<CAPTION>
    Supplemental
    Indenture Date             Parties                                           Providing For
    <S>                        <C>                                               <C>
    August 1, 1944             Company to Continental Illinois National Bank     Amendment and restatement of
                               and Trust Company of Chicago and Edmond B.        Mortgage dated July 1, 1923
                               Stofft, as Trustee and Co-Trustee

    August 1, 1946             Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Edmond B.
                               Stofft, as Trustee and Co-Trustee

    April 1, 1953              Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Edmond B.
                               Stofft, as Trustee and Co-Trustee
</TABLE>

                                       -1-

<PAGE>

<TABLE>
<CAPTION>
    Supplemental
    Indenture Date             Parties                                           Providing For
    <S>                        <C>                                               <C>
    March 31, 1967             Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Edward J.
                               Friedrich, as Trustee and Co-Trustee

    April 1, 1967              Company to Continental Illinois National Bank     Amendment of Sections 3.01, 3.02,
                               and Trust Company of Chicago and Edward J.        3.05 and 3.14 of the Mortgage and
                               Friedrich, as Trustee and Co-Trustee              issuance of First Mortgage 5-3/8%
                                                                                 Bonds, Series Y

    February 28, 1969          Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    May 29, 1970               Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    June 1, 1971               Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    April 1, 1972              Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    May 31, 1972               Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    June 15, 1973              Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    May 31, 1974               Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    June 13, 1975              Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    May 28, 1976               Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    June 3, 1977               Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee
</TABLE>

                                       -2-

<PAGE>

<TABLE>
<CAPTION>
    Supplemental
    Indenture Date             Parties                                           Providing For
    <S>                        <C>                                               <C>
    May 17, 1978               Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    August 31, 1978            Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    June 18, 1979              Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    June 20, 1980              Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    April 16, 1981             Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    April 30, 1982             Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    April 15, 1983             Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    April 13, 1984             Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    April 15, 1985             Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and Donald W.
                               Alfvin, as Trustee and Co-Trustee

    April 15, 1986             Company to Continental Illinois National Bank     Confirmation of mortgage lien
                               and Trust Company of Chicago and M.J. Kruger,
                               as Trustee and Co-Trustee

    June 15, 1990              Company to Continental Bank, National             Issuance of First Mortgage 9-7/8%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 75
                               Co-Trustee

    October 1, 1991            Company to Continental Bank, National             Issuance of First Mortgage 8-1/4%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 76 and First
                               Co-Trustee                                        Mortgage 8-7/8% Bonds, Series 77
</TABLE>

                                       -3-

<PAGE>

<TABLE>
<CAPTION>
    Supplemental
    Indenture Date             Parties                                           Providing For
    <S>                        <C>                                               <C>
    October 15, 1991           Company to Continental Bank, National             Issuance of First Mortgage 8-3/8%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 78 and First
                               Co-Trustee                                        Mortgage 9-1/8% Bonds, Series 79

    May 15, 1992               Company to Continental Bank, National             Issuance of First Mortgage 6-1/8%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 82 and First
                               Co-Trustee                                        Mortgage 8% Bonds, Series 83

    September 15, 1992         Company to Continental Bank, National             Issuance of First Mortgage 7-3/8%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 85 and First
                               Co-Trustee                                        Mortgage 8-3/8% Bonds, Series 86

    February 1, 1993           Company to Continental Bank, National             Issuance of First Mortgage 8-3/8%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 88
                               Co-Trustee

    April 1, 1993              Company to Continental Bank, National             Issuance of First Mortgage 6-1/2%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 90 and First
                               Co-Trustee                                        Mortgage 8% Bonds, Series 91

    April 15, 1993             Company to Continental Bank, National             Issuance of First Mortgage 7-5/8%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 92
                               Co-Trustee

    June 15, 1993              Company to Continental Bank, National             Issuance of First Mortgage 7%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 93 and First
                               Co-Trustee                                        Mortgage 7-1/2% Bonds, Series 94

    July 15, 1993              Company to Continental Bank, National             Issuance of First Mortgage 6-5/8%
                               Association and M.J. Kruger, as Trustee and       Bonds, Series 96 and First
                               Co-Trustee                                        Mortgage 7-3/4% Bonds, Series 97

    January 15, 1994           Company to Continental Bank, National             Issuance of First Mortgage Bonds,
                               Association and M.J. Kruger, as Trustee and       Pollution Control Series 1994A,
                               Co-Trustee                                        1994B and 1994C

    December 1, 1994           Company to Bank of America Illinois and           Issuance of First Mortgage Bonds,
                               Robert J. Donahue, as Trustee and Co-Trustee      Pollution Control Series 1994D

    June 1, 1996               Company to Harris Trust and Savings Bank and      Issuance of First Mortgage Bonds,
                               D.G. Donovan, as Trustee and Co-Trustee           Pollution Control Series 1996A and
                                                                                 1996B

    March 1, 2002              Company to BNY Midwest Trust Company and D.G.     Issuance of unregistered First
                               Donovan, as Trustee and Co-Trustee                Mortgage 6.15% Bonds, Series 98

    May 20, 2002               Company to BNY Midwest Trust Company and D.G.     Issuance of First Mortgage Bonds,
                               Donovan, as Trustee and Co-Trustee                Pollution Control Series 2002
</TABLE>

                                       -4-

<PAGE>

<TABLE>
<CAPTION>
   Supplemental
   Indenture Date             Parties                                           Providing For
   <S>                        <C>                                               <C>
   June 1, 2002               Company to BNY Midwest Trust Company and D.G.     Issuance of additional
                              Donovan, as Trustee and Co-Trustee                unregistered First Mortgage 6.15%
                                                                                Bonds, Series 98

   October 7, 2002            Company to BNY Midwest Trust Company and D.G.     Issuance of registered First
                              Donovan, as Trustee and Co-Trustee                Mortgage 6.15% Bonds, Series 98 in
                                                                                exchange for unregistered First
                                                                                Mortgage 6.15% Bonds, Series 98

   January 13, 2002           Company to BNY Midwest Trust Company and D.G.     Issuance of First Mortgage 3.700%
                              Donovan, as Trustee and Co-Trustee                Bonds, Series 99 and First
                                                                                Mortgage 5.875% Bonds, Series 100
</TABLE>

     WHEREAS, the respective designations, maturity dates and principal amounts
of the bonds of each series presently outstanding under, and secured by, the
Mortgage and the several supplemental indentures above referred to, are as
follows:

<TABLE>
<CAPTION>
                   Designation                            Maturity Date                Principal Amount
   <S>                                                    <C>                          <C>
   First Mortgage 9-7/8% Bonds, Series 75                 June 15, 2020                 $   54,171,000

   First Mortgage 8-1/4% Bonds, Series 76                 October 1, 2006                  100,000,000

   First Mortgage 8-3/8% Bonds, Series 78                 October 15, 2006                 125,000,000

   First Mortgage 8% Bonds, Series 83                     May 15, 2008                     140,000,000

   First Mortgage 8-3/8% Bonds, Series 88                 February 15, 2023                235,950,000

   First Mortgage 8% Bonds, Series 91                     April 15, 2023                   160,000,000

   First Mortgage 7-5/8% Bonds, Series 92                 April 15, 2013                   218,500,000

   First Mortgage 7% Bonds, Series 93                     July 1, 2005                     225,000,000

   First Mortgage 7-1/2% Bonds, Series 94                 July 1, 2013                     147,000,000

   First Mortgage 6-5/8% Bonds, Series 96                 July 15, 2003                    100,000,000

   First Mortgage 7-3/4% Bonds, Series 97                 July 15, 2023                    150,000,000

   First Mortgage 5.3% Bonds, Pollution                   January 15, 2004                  26,000,000
   Control Series1994A

   First Mortgage 5.7% Bonds, Pollution                   January 15, 2009                  20,000,000
   Control Series 1994B

   First Mortgage 5.85% Bonds, Pollution                  January 15, 2014                  20,000,000
   Control Series 1994C

   First Mortgage 6.75% Bonds, Pollution                  March 1, 2015                     91,000,000
</TABLE>

                                       -5-

<PAGE>

<TABLE>
<CAPTION>
                   Designation                            Maturity Date                Principal Amount
   <S>                                                    <C>                          <C>
   Control Series 1994D

   First Mortgage 4.4% Bonds, Pollution                   December 1, 2006                   110,000,000
   Control Series 1996A

   First Mortgage 4.4% Bonds, Pollution                   December 1, 2006                    89,400,000
   Control Series 1996B

   First Mortgage 6.15% Bonds, Series 98                  March 15, 2012                     600,000,000

   First Mortgage Bonds, Pollution Control                April 15, 2013                     100,000,000
   Series 2002

   First Mortgage 3.700% Bonds, Series 99                 February 1, 2008                   350,000,000

   First Mortgage 5.875% Bonds, Series 100                February 1, 2033                   350,000,000
                                                                                       -----------------
                                                          Total                           $3,412,021,000
                                                                                       =================
</TABLE>

     WHEREAS, the Mortgage provides for the issuance from time to time
thereunder, in series, of bonds of the Company for the purposes and subject to
the limitations therein specified; and

     WHEREAS, the Company desires, by this Supplemental Indenture, to create an
additional series of bonds to be issuable under the Mortgage, such bonds to be
designated "First Mortgage 4.70% Bonds, Series 101" (hereinafter called the
"bonds of Series 101") and the terms and provisions to be contained in the bonds
of Series 101 or to be otherwise applicable thereto to be as set forth in this
Supplemental Indenture; and

     WHEREAS, the bonds of Series 101 and the Trustee's certificate to be
endorsed thereon shall be substantially in the form of the General Form of
Registered Bond Without Coupons and the form of the General Form of Trustee's
Certificate set forth in Section 3.05 of the Supplemental Indenture dated August
1, 1944 to the Mortgage with such appropriate insertions, omissions and
variations in order to express the designation, date, maturity date, annual
interest rate, record dates for, and dates of, payment of interest,
denominations, terms of redemption and redemption prices, and other terms and
characteristics authorized or permitted by the Mortgage or not inconsistent
therewith; and

     WHEREAS, the Company is legally empowered and has been duly authorized by
the necessary corporate action and by orders of the Illinois Commerce Commission
to make, execute and deliver this Supplemental Indenture, and to create, as an
additional series of bonds of the

     Company, the bonds of Series 101, and all acts and things whatsoever
necessary to make this Supplemental Indenture, when executed and delivered by
the Company and the Trustees, a valid, binding and legal instrument, and to make
the bonds of Series 101, when authenticated by the

                                      -6-

<PAGE>

Trustee and issued as in the Mortgage and in this Supplemental Indenture
provided, the valid, binding and legal obligations of the Company, entitled in
all respects to the security of the Mortgage, as amended and supplemented, have
been done and performed;

     NOW, THEREFORE, in consideration of the premises and of the sum of one
dollar duly paid by the Trustees to the Company, and for other good and valuable
consideration, the receipt of which is hereby acknowledged, the parties hereto
do hereby agree as follows:

     SECTION 1. Designation and Issuance of Bonds of Series 101. The bonds of
Series 101 shall, as hereinbefore recited, be designated as the Company's "First
Mortgage 4.70% Bonds, Series 101." Subject to the provisions of the Mortgage,
the bonds of Series 101 shall be issuable without limitation as to the aggregate
principal amount thereof.

     SECTION 2. Form, Date, Maturity Date, Interest Rate and Interest Payment
Dates of Bonds of Series 101. (a) The definitive bonds of Series 101 shall be in
engraved, lithographed, printed or typewritten form and shall be registered
bonds without coupons; and such bonds and the Trustee's certificate to be
endorsed thereon shall be substantially in the forms hereinbefore recited,
respectively. The bonds of Series 101 shall be dated as provided in Section 3.01
of the Mortgage, as amended by Supplemental Indenture dated April 1, 1967.

     (b)  The bonds of Series 101 shall mature on April 15, 2015.

     (c)  The bonds of Series 101 shall bear interest at the rate of 4.70% per
annum until the principal thereof shall be paid.

     (d)  Interest on the bonds of Series 101 shall be payable semi-annually on
the fifteenth day of April and the fifteenth day of October in each year,
commencing October 15, 2003. April 1 and October 1 in each year are hereby
established as record dates for the payment of interest payable on the next
succeeding interest payment dates, respectively. The interest on each bond of
Series 101 so payable on any interest payment date shall, subject to the
exceptions provided in Section 3.01 of the Mortgage, as amended by said
Supplemental Indenture dated April 1, 1967, be paid to the person in whose name
such bond is registered at the close of business on the April 1 or October 1, as
the case may be, next preceding such interest payment date.

     SECTION 3. Execution of Bonds of Series 101. The bonds of Series 101 shall
be executed on behalf of the Company by its President or one of its Vice
Presidents, manually or by facsimile signature, and shall have its corporate
seal affixed thereto or a facsimile of such seal imprinted thereon, attested by
its Secretary or one of its Assistant Secretaries, manually or by facsimile
signature, all as may be provided by resolution of the Board of Directors of the
Company. In case any officer or officers whose signature or signatures, manual
or facsimile, shall appear upon any bond of Series 101 shall cease to be such
officer or officers before such bond shall have been actually authenticated and
delivered, such bond nevertheless may be issued, authenticated and delivered
with the same force and effect as though the person or persons whose

                                       -7-

<PAGE>

signature or signatures, manual or facsimile, appear thereon had not ceased to
be such officer or officers of the Company.

     SECTION 4. Medium and Places of Payment of Principal of and Interest on
Bonds of Series 101; Transferability and Exchangeability. Both the principal of
and interest on the bonds of Series 101 shall be payable in any coin or currency
of the United States of America which at the time of payment is legal tender for
the payment of public and private debts, and both such principal and interest
shall be payable at the office or agency of the Company in the City of Chicago,
State of Illinois, or, at the option of the registered owner, at the office or
agency of the Company in the Borough of Manhattan, The City of New York, State
of New York, and such bonds shall be transferable and exchangeable, in the
manner provided in Sections 3.09 and 3.10 of the Mortgage, at said office or
agency. No charge shall be made by the Company to the registered owner of any
bond of Series 101 for the transfer of such bond or for the exchange thereof for
bonds of other authorized denominations, except, in the case of transfer, a
charge sufficient to reimburse the Company for any stamp or other tax or
governmental charge required to be paid by the Company or the Trustee.

     SECTION 5. Denominations and Numbering of Bonds of Series 101. The bonds of
Series 101 shall be issued in the denomination of $1,000 and in such multiples
of $1,000 as shall from time to time hereafter be determined and authorized by
the Board of Directors of the Company or by any officer or officers of the
Company authorized to make such determination, the authorization of the
denomination of any bond of Series 101 to be conclusively evidenced by the
execution thereof on behalf of the Company. Bonds of Series 101 shall be
numbered R-1 and consecutively upwards.

     SECTION 6. Temporary Bonds of Series 101. Until definitive bonds of Series
101 are ready for delivery, there may be authenticated and issued in lieu of any
thereof and subject to all of the provisions, limitations and conditions set
forth in Section 3.11 of the Mortgage, temporary registered bonds without
coupons of Series 101.

     SECTION 7. Redemption of Bonds of Series 101. (a) The bonds of Series 101
shall be redeemable, at the option of the Company, as a whole or in part, at any
time upon notice sent by the Company through the mail, postage prepaid, at least
thirty (30) days and not more than forty-five (45) days prior to the date fixed
for redemption, to the registered holder of each bond to be redeemed in whole or
in part, addressed to such holder at his address appearing upon the registration
books, at a redemption price equal to the greater of

          (1)  100% of the principal amount of the bonds of Series 101 to be
     redeemed, plus accrued interest to the redemption date, or

          (2)  as determined by the Quotation Agent (as hereinafter defined),
     the sum of the present values of the remaining scheduled payments of
     principal and interest on the bonds of Series 101 to be redeemed (not
     including any portion of payments of interest

                                       -8-

<PAGE>

     accrued as of the redemption date) discounted to the redemption date on a
     semi-annual basis (assuming a 360-day year consisting of twelve 30-day
     months) at the Adjusted Treasury Rate (as hereinafter defined) plus
     twenty-five (25) basis points, plus accrued interest to the redemption
     date.

Unless the Company defaults in payment of the redemption price, on and after the
redemption date, interest will cease to accrue on the bonds of Series 101 or
portions of the bonds of Series 101 called for redemption.

     (b)  For purposes of the foregoing Section 7(a), the following terms shall
have the respective meanings set forth below:

          "Adjusted Treasury Rate" means, with respect to any redemption date,
     the rate per year 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 the redemption date.

          "Business Day" means any day that is not a day on which banking
     institutions in New York City are authorized or required by law or
     regulation to close.

          "Comparable Treasury Issue" means the United States Treasury security
     selected by the Quotation Agent as having a maturity comparable to the
     remaining term of the bonds of Series 101 that would be used, 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 bonds of Series 101.

          "Comparable Treasury Price" means, with respect to any redemption
     date:

               (i)  the average of the Reference Treasury Dealer Quotations for
          that redemption date, after excluding the highest and lowest of the
          Reference Treasury Dealer Quotations; or

               (ii) if the Trustee obtains fewer than three Reference Treasury
          Dealer Quotations, the average of all Reference Treasury Dealer
          Quotations so received.

          "Quotation Agent" means the Reference Treasury Dealer appointed by the
     Company.

          "Reference Treasury Dealer" means (1) each of Merrill Lynch, Pierce,
     Fenner & Smith Incorporated and ABN AMRO Incorporated and their respective
     successors, unless any of them ceases to be a primary U.S. Government
     securities dealer in New York City (a "Primary Treasury Dealer"), in which
     case the Company shall substitute another Primary Treasury Dealer; and (2)
     any other Primary Treasury Dealer selected by the Company.

                                       -9-

<PAGE>

          "Reference Treasury Dealer Quotations" means, with respect to each
     Reference Treasury Dealer and any redemption date, the average, as
     determined by the Trustee, of the bid and asked prices for the Comparable
     Treasury Issue (expressed in each case as a percentage of its principal
     amount) quoted in writing to the Trustee by that Reference Treasury Dealer
     at 5:00 p.m., New York City time, on the third Business Day preceding that
     redemption date.

     (c) In case the Company shall desire to exercise such right to redeem and
pay off all or any part of such bonds of Series 101 as hereinbefore provided, it
shall comply with all the terms and provisions of Article V of the Mortgage
applicable thereto, and such redemption shall be made under and subject to the
terms and provisions of Article V and in the manner and with the effect therein
provided, but at the time or times and upon mailing of notice, all as
hereinbefore set forth in this Section 7. No publication of notice of any
redemption of any bonds of Series 101 shall be required under Section 5.03(a) of
the Mortgage.

     SECTION 8. Book-Entry Only System. It is intended that the bonds of Series
101 be registered so as to participate in the securities depository system (the
"DTC System") with The Depository Trust Company ("DTC"), as set forth herein.
The bonds of Series 101 shall be initially issued in the form of a fully
registered bond or bonds in the name of Cede & Co., or any successor thereto, as
nominee for DTC. The Company and the Trustees are authorized to execute and
deliver such letters to or agreements with DTC as shall be necessary to
effectuate the DTC System, including the Letter of Representations from the
Company and the Trustees to DTC relating to the bonds of Series 101 (the
"Representation Letter"). In the event of any conflict between the terms of the
Representation Letter and the Mortgage, the terms of the Mortgage shall control.
DTC may exercise the rights of a bondholder only in accordance with the terms
hereof applicable to the exercise of such rights.

     With respect to bonds of Series 101 registered in the name of DTC or its
nominee, the Company and the Trustees shall have no responsibility or obligation
to any broker-dealer, bank or other financial institution for which DTC holds
such bonds from time to time as securities depository (each such broker-dealer,
bank or other financial institution being referred to herein as a "Depository
Participant") or to any person on behalf of whom such a Depository Participant
holds an interest in such bonds (each such person being herein referred to as an
"Indirect Participant"). Without limiting the immediately preceding sentence,
the Company and the Trustees shall have no responsibility or obligation with
respect to:

          (i)  the accuracy of the records of DTC, its nominee or any Depository
     Participant with respect to any ownership interest in the bonds of Series
     101,

          (ii) the delivery to any Depository Participant or any Indirect
     Participant or any other person, other than a registered owner of a bond of
     Series 101, of any notice with respect to the bonds of Series 101,
     including any notice of redemption,

                                      -10-

<PAGE>

          (iii) the payment to any Depository Participant or Indirect
     Participant or any other person, other than a registered owner of a bond of
     Series 101, of any amount with respect to principal of, redemption premium,
     if any, on, or interest on, the bonds of Series 101, or

          (iv)  any consent given by DTC as registered owner.

So long as certificates for the bonds of Series 101 are not issued as
hereinafter provided, the Company and the Trustees may treat DTC or any
successor securities depository as, and deem DTC or any successor securities
depository to be, the absolute owner of such bonds for all purposes whatsoever,
including, without limitation, (1) the payment of principal and interest on such
bonds, (2) giving notice of matters (including redemption) with respect to such
bonds and (3) registering transfers with respect to such bonds. While a bond of
Series 101 is in the DTC System, no person other than DTC or its nominee shall
receive a certificate with respect to such bond.

     In the event that:

          (a)   DTC notifies the Company that it is unwilling or unable to
     continue as depositary or if DTC ceases to be a clearing agency registered
     under applicable law and a successor depositary is not appointed by the
     Company within 90 days,

          (b)   the Company determines that the beneficial owners of the bonds
     of Series 101 should be able to obtain certificated bonds and so notifies
     the Trustees in writing or

          (c) there shall have occurred and be continuing a completed default or
     any event which after notice or lapse of time or both would be a completed
     default with respect to the bonds of Series 101,

the bonds of Series 101 shall no longer be restricted to being registered in the
name of DTC or its nominee. In the case of clause (a) of the preceding sentence,
the Company may determine that the bonds of Series 101 shall be registered in
the name of and deposited with a successor depository operating a securities
depository system, as may be acceptable to the Company and the Trustees, or such
depository's agent or designee, and if the Company does not appoint a successor
securities depository system within 90 days, then the bonds may be registered in
whatever name or names registered owners of bonds transferring or exchanging
such bonds shall designate, in accordance with the provisions hereof.

     Notwithstanding any other provision of the Mortgage to the contrary, so
long as any bond of Series 101 is registered in the name of DTC or its nominee,
all payments with respect to principal of and interest on such bond and all
notices with respect to such bond shall be made and given, respectively, in the
manner provided in the Representation Letter.

                                      -11-

<PAGE>

     SECTION 9.  Legends. So long as the bonds of Series 101 are held by DTC,
such bonds of Series 101 shall bear the following legend:

          Unless this bond is presented by an authorized representative of the
     Depository Trust Company, a New York corporation ("DTC"), to the Company or
     its agent for registration of transfer, exchange or payment, and any bond
     issued is registered in the name of Cede & Co. or in such other name as is
     requested by an authorized representative of DTC (and any payment is made
     to Cede & Co. or to such other entity as is requested by an authorized
     representative of DTC), any transfer, pledge or other use hereof for value
     or otherwise by a person is wrongful inasmuch as the registered owner
     hereof, Cede & Co., has an interest herein.

     SECTION 10. Confirmation of Lien. The Company, for the equal and
proportionate benefit and security of the holders of all bonds at any time
issued under the Mortgage, hereby confirms the lien of the Mortgage upon, and
hereby grants, bargains, sells, transfers, assigns, pledges, mortgages, warrants
and conveys unto the Trustees, all property of the Company and all property
hereafter acquired by the Company, other than (in each case) property which, by
virtue of any of the provisions of the Mortgage, is excluded from such lien, and
hereby confirms the title of the Trustees (as set forth in the Mortgage) in and
to all such property. Without in any way limiting or restricting the generality
of the foregoing, there is specifically included within the confirmation of lien
and title hereinabove expressed the property of the Company legally described on
Exhibit A attached hereto and made a part hereof.

     SECTION 11. Miscellaneous. The terms and conditions of this Supplemental
Indenture shall be deemed to be a part of the terms and conditions of the
Mortgage for any and all purposes. The Mortgage, as supplemented by said
indentures supplemental thereto dated subsequent to August 1, 1944 and referred
to in the recitals of this Supplemental Indenture, and as further supplemented
by this Supplemental Indenture, is in all respects hereby ratified and
confirmed.

     This Supplemental Indenture shall bind and, subject to the provisions of
Article XIV of the Mortgage, inure to the benefit of the respective successors
and assigns of the parties hereto.

     Although this Supplemental Indenture is dated as of March 14, 2003, it
shall be effective only from and after the actual time of its execution and
delivery by the Company and the Trustees on the date indicated by their
respective acknowledgments hereto annexed.

     This Supplemental Indenture may be simultaneously executed in any number of
counterparts, and all such counterparts executed and delivered, each as an
original, shall constitute but one and the same instrument.

                                      -12-

<PAGE>

     IN WITNESS WHEREOF, Commonwealth Edison Company has caused this
Supplemental Indenture to be executed in its name by its Vice President and
Treasurer, and attested by one of its Assistant Secretaries, and BNY Midwest
Trust Company, as Trustee under the Mortgage, has caused this Supplemental
Indenture to be executed in its name by one of its Vice Presidents, and attested
by one of its Assistant Vice Presidents, and D. G. Donovan, as Co-Trustee under
the Mortgage, has hereunto affixed his signature, all as of the day and year
first above written.

                                              COMMONWEALTH EDISON COMPANY


                                              By  /s/ J. Barry Mitchell
                                                  J. Barry Mitchell
                                                  Vice President and Treasurer

ATTEST:

     /s/ Scott N. Peters
     Scott N. Peters
     Assistant Secretary

                                              BNY MIDWEST TRUST COMPANY


                                              By  /s/ J. Bartolini
                                                  J. Bartolini
                                                  Vice President

ATTEST:

     /s/ C. Potter
     C. Potter
     Assistant Vice President

                                              /s/ D. G. Donovan
                                              D. G. DONOVAN

                                      -13-

<PAGE>

STATE OF ILLINOIS )
                      ) SS.
COUNTY OF COOK    )



     I, MARY L. KWILOS, a Notary Public in and for said County, in the State
aforesaid, DO HEREBY CERTIFY that J. Barry Mitchell, Vice President and
Treasurer of Commonwealth Edison Company, an Illinois corporation, one of the
parties described in and which executed the foregoing instrument, and Scott N.
Peters, an Assistant Secretary of said corporation, who are both personally
known to me to be the same persons whose names are subscribed to the foregoing
instrument as such Vice President and Treasurer and Assistant Secretary,
respectively, and who are both personally known to me to be Vice President and
Treasurer and an Assistant Secretary respectively, of said corporation, appeared
before me this day in person and severally acknowledged that they signed,
executed and delivered said instrument as their free and voluntary act as such
Vice President and Treasurer and Assistant Secretary, respectively, of said
corporation, and as the free and voluntary act of said corporation, for the uses
and purposes therein set forth.

     GIVEN under my hand and notarial seal this 28/th/ day of March, A.D. 2003.


                                              /s/ Mary L. Kwilos
                                              Mary L. Kwilos
                                              Notary Public

(NOTARIAL SEAL)


My Commission expires October 26, 2005.

                                      -14-

<PAGE>

STATE OF ILLINOIS )
                      ) SS.
COUNTY OF COOK    )


I, L. GARCIA, a Notary Public in and for said County, in the State aforesaid, DO
HEREBY CERTIFY that J. Bartolini, a Vice President of BNY Midwest Trust Company,
an Illinois trust company, one of the parties described in and which executed
the foregoing instrument, and C. Potter, an Assistant Vice President of said
trust company, who are both personally known to me to be the same persons whose
names are subscribed to the foregoing instrument as such Vice President and
Assistant Vice President, respectively, and who are both personally known to me
to be a Vice President and an Assistant Vice President, respectively, of said
trust company, appeared before me this day in person and severally acknowledged
that they signed, executed and delivered said instrument as their free and
voluntary act as such Vice President and Assistant Vice President, respectively,
of said trust company, and as the free and voluntary act of said trust company,
for the uses and purposes therein set forth.

     GIVEN under my hand and notarial seal this 14/th/ day of March, A.D. 2003.




                                              /s/ L. Garcia
                                              L. Garcia
                                              Notary Public

(NOTARIAL SEAL)


My Commission expires July 8, 2006.

                                      -15-

<PAGE>

STATE OF ILLINOIS )
                       ) SS.
COUNTY OF COOK    )




I, L. GARCIA, a Notary Public in and for said County, in the State aforesaid, DO
HEREBY CERTIFY that D. G. DONOVAN, one of the parties described in and which
executed the foregoing instrument, who is personally known to me to be the same
person whose name is subscribed to the foregoing instrument, appeared before me
this day in person and acknowledged that he signed, executed and delivered said
instrument as his free and voluntary act for the uses and purposes therein set
forth.

     GIVEN under my hand and notarial seal this 14/th/ day of March, A.D. 2003.





                                              /s/ L. Garcia
                                              L. Garcia
                                              Notary Public

(NOTARIAL SEAL)


My Commission expires July 8, 2006.

                                      -16-