SUPPLEMENTAL INDENTURE

Exhibit 4.1

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

Richard W. Astle
Sidley Austin LLP
One South Dearborn Street
Chicago, Illinois 60603

Supplemental Indenture
Dated as of September 15, 2006
Commonwealth Edison Company
to
BNY Midwest Trust Company
and
D.G. Donovan
Trustees Under Mortgage Dated July 1, 1923,
and Certain
Indentures Supplemental Thereto

Giving Notice of the Issuance of Additional
FIRST MORTGAGE 5.95% BONDS, SERIES 104
Due August 15, 2016

      This Supplemental Indenture , dated as of September 15, 2006, 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 440 South LaSalle Street, Suite 3300, Chicago, Illinois 60605, party of the first part, BNY Midwest Trust Company , a trust 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:

(the Supplemental Indenture dated as of August 1, 2006 referenced above, a copy of which (without Exhibits thereto) is attached hereto as Exhibit A , is referred to herein as the " August 2006 Supplemental Indenture ”); and

     WHEREAS, the respective designations, maturity dates and stated 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:

     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, pursuant to the August 2006 Supplemental Indenture, the Company issued “bonds of Series 104” (as defined in the August 2006 Supplemental Indenture) under and pursuant to the Mortgage, and, pursuant to said August 2006 Supplemental Indenture, the Company has the right to issue additional bonds of Series 104; and

     WHEREAS, the Company desires to issue additional bonds of Series 104 under the Mortgage (including the August 2006 Supplemental Indenture) in the aggregate principal amount of One Hundred Fifteen Million Dollars ($115,000,000.00) (the “ Additional bonds of Series 104 ”), such bonds to be governed by the terms, provisions and conditions set forth in the August 2006 Supplemental Indenture; and

     WHEREAS, the Company desires to execute and deliver this Supplemental Indenture for purposes of providing notice of the issuance of the Additional bonds of Series 104 under and pursuant to the Mortgage and confirming that such Additional bonds of Series 104 are secured by the lien of the Mortgage, as further provided herein; and

     WHEREAS, the Company is legally empowered and has been duly authorized by the necessary corporate action and by order of the Illinois Commerce Commission to make, execute and deliver this Supplemental Indenture, and to issue the Additional bonds of Series 104, 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 Additional bonds of Series 104, when authenticated by the 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 Additional Bonds of Series 104 . The Additional bonds of Series 104 shall, as provided in the August 2006 Supplemental Indenture, be designated as additional “First Mortgage 5.95% Bonds, Series 104.” The Additional bonds of Series 104 shall, for all purposes, constitute “bonds of Series 104” for purposes of the Mortgage, shall be governed by each and all of the terms, provisions and conditions set forth in the August 2006 Supplemental Indenture, and shall be secured by the Mortgage. The parties confirm that, subject to the provisions of the Mortgage, the bonds of Series 104 shall be issuable without limitation as to the aggregate principal amount thereof.

      SECTION 2. 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 B attached hereto and made a part hereof.

      SECTION 3. 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 September 15, 2006, 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.

     Notwithstanding anything to the contrary contained in the Mortgage, the maximum amount of indebtedness secured by the Mortgage shall not exceed 200% of the aggregate stated principal amount of the bonds of each series presently outstanding under, and secured by, the Mortgage, as set forth in the Recitals to this Supplemental Indenture, except to the extent such maximum amount may be adjusted by a subsequent recorded supplemental indenture (which adjustment, and the corresponding supplemental indenture, shall not require the consent or

approval of the holders of any bonds then outstanding under the Mortgage, including the holders of the bonds of Series 104).

     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.

     IN WITNESS WHEREOF, Commonwealth Edison Company has caused this Supplemental Indenture to be executed in its name by its Senior Vice President, Chief Financial Officer and Treasurer, and attested by its Secretary, 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 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.

ATTEST:

/s/ Donna Massey
Donna Massey
Secretary

ATTEST:

/s/ M. Callahan
M. Callahan
Vice President

     I, MARY E. NOLAN, a Notary Public in and for said County, in the State aforesaid, DO HEREBY CERTIFY that Robert K. McDonald, Senior Vice President, Chief Financial Officer and Treasurer of Commonwealth Edison Company, an Illinois corporation, one of the parties described in and which executed the foregoing instrument, and Donna Massey, 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 Senior Vice President, Chief Financial Officer and Treasurer and Secretary, respectively, and who are both personally known to me to be Senior Vice President, Chief Financial Officer and Treasurer and 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 Senior Vice President, Chief Financial Officer and Treasurer and 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 25 ^th day of September, A.D. 2006.

(NOTARIAL SEAL)

My Commission expires April 23, 2009.

     I, T. MOSTERD, a Notary Public in and for said County, in the State aforesaid, DO HEREBY CERTIFY that J. BARTOLINI, Vice President of BNY Midwest Trust Company, an Illinois trust company, one of the parties described in and which executed the foregoing instrument, and M. CALLAHAN, 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 Presidents, and who are both personally known to me to be Vice Presidents 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 Presidents 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 20 ^th day of September, A.D. 2006.

{SEAL}

My Commission expires January 22, 2009.

     I, T. MOSTERD, 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 20 ^th day of September, A.D. 2006.

{SEAL}

My Commission expires January 22, 2009.

EXHIBIT A

AUGUST 2006 SUPPLEMENTAL INDENTURE

See attached.

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

Richard W. Astle
Sidley Austin LLP
One South Dearborn Street
Chicago, Illinois 60603

Supplemental Indenture

Dated as of August 1, 2006

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 5.95% BONDS, SERIES 104
Due August 15, 2016

      This Supplemental Indenture , dated as of August 1, 2006, 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 440 South LaSalle Street, Suite 3300, Chicago, Illinois 60605, party of the first part, BNY Midwest Tr