Exelon Generation Company, LLC 6.25% Senior Notes due 2039

Exhibit 4.2

FORM OF 6.25% SENIOR NOTE DUE 2039

THIS NOTE IS A REGISTERED GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITORY OR A NOMINEE OF A DEPOSITORY OR A SUCCESSOR DEPOSITORY. THIS NOTE IS NOT EXCHANGEABLE FOR SECURITIES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE DEPOSITORY OR ITS NOMINEE EXCEPT IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND NO TRANSFER OF THIS NOTE (OTHER THAN A TRANSFER OF THIS NOTE AS A WHOLE BY THE DEPOSITORY TO A NOMINEE OF THE DEPOSITORY OR BY A NOMINEE OF THE DEPOSITORY TO THE DEPOSITORY OR ANOTHER NOMINEE OF THE DEPOSITORY) MAY BE REGISTERED EXCEPT IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE. UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE, OR PAYMENT, AND ANY CERTIFICATE 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 OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO. HAS AN INTEREST HEREIN.

Exelon Generation Company, LLC

6.25% Senior Notes due 2039

Exelon Generation Company, LLC, a limited liability company duly organized and subsisting under the laws of the Commonwealth of Pennsylvania (herein called the “Issuer” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., or registered assigns, the principal sum of              Million Dollars ($            ), and to pay interest thereon from September 23, 2009 or from the most recent interest payment date to which interest has been paid or duly provided for, semi-annually on April 1 and October 1 in each year, beginning April 1, 2010 at the rate of 6.25% per annum, until the principal hereof is paid or made available for payment, provided that any principal and premium, and any such installment of interest, which is overdue shall bear interest at the rate of 6.25% per annum (to the extent that the payment of such interest shall be legally enforceable), from the dates such amounts are due until they are paid or made available for payment, and such interest shall be payable on demand. Interest on this Note shall be computed on the basis of a 360-day year composed of twelve 30-day months. The interest so payable, and punctually paid or duly provided for, on any interest payment date will, as provided in such Indenture, be paid to the Person in whose name this Note (or one or more predecessor Securities) is registered at the close of business on the record date for such interest, which shall be March 15 or September 15 (whether or not a Business Day), as the case may be, next preceding such interest payment date. Any such interest not so punctually paid or duly provided

for will forthwith cease to be payable to the Holder on such record date and may either be paid to the Person in whose name this Note (or one or more predecessor Securities) is registered at the close of business on a special record date for the payment of such defaulted interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not less than 10 days prior to such special record date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

Payment of the principal of (and premium, if any) and interest on this Note will be made at the office or agency of the Issuer maintained for that purpose in the Borough of Manhattan, the City of New York, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided that so long as the Notes are held by DTC as Registered Global Securities, payments shall be made by wire transfer to DTC.

Reference is hereby made to the further provisions of this Note set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Note shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF the Issuer has caused this instrument to be duly executed.

[Reverse of Note]

This Note is one of a duly authorized issue of securities of the Issuer (herein called the “Notes”), issued and to be issued in one or more series under an Indenture, dated as of September 28, 2007 (herein called the “Indenture”), between the Issuer and U.S. Bank National Association, as trustee (herein called the “Trustee”, which term includes any successor trustee under the Indenture), and reference is hereby made to the Indenture, including the Officer’s Certificate, dated as of September 23, 2009, delivered pursuant to Sections 2.1, 2.4(3) and 10.5 of the Indenture and setting forth additional