SUMMARY

This summary highlights selected information contained in this joint proxy statement/prospectus and does not contain all the information that may be important to you. Exelon and Constellation urge you to read carefully this joint proxy statement/prospectus in its entirety, as well as the annexes. Additional, important information is also contained in the documents incorporated by reference into this joint proxy statement/prospectus; see the section entitled “Where You Can Find More Information” beginning on page 197.

The Companies (See page 31)

Exelon

Exelon was incorporated in Pennsylvania in February 1999. Exelon’s principal executive offices are located at 10 South Dearborn Street, Chicago, Illinois 60603, and its telephone number is 800-483-3220. Exelon is one of the nation’s largest energy companies with approximately $18 billion in annual revenues. Exelon distributes electricity to approximately 5.4 million customers in northern Illinois and southeastern Pennsylvania and natural gas to approximately 490,000 customers in the Philadelphia area. Exelon’s operations include energy generation, power marketing and energy delivery. Exelon has one of the industry’s largest portfolios of electricity generation capacity, with a nationwide reach and strong positions in the Midwest and Mid-Atlantic. Exelon is a leading advocate for clean, environmentally sustainable energy sources, such as wind, solar power and nuclear energy, and operates the largest nuclear fleet in the United States. Exelon trades on the NYSE under the ticker “EXC.”

Constellation

Constellation was incorporated in Maryland in September 1995. Constellation’s principal executive offices are located at 100 Constellation Way, Baltimore, Maryland 21202, and its telephone number is 410-470-2800. Constellation is a leading competitive supplier of power, natural gas and energy products and services for homes and businesses across the continental United States. Constellation owns a diversified fleet of generating units, totaling approximately 12,000 megawatts of generating capacity, and is a leading advocate for clean, environmentally sustainable energy sources, such as solar power and nuclear energy. In central Maryland, the company delivers electricity and natural gas through BGE, its regulated utility. Constellation had revenues of $14.3 billion in 2010. Constellation trades on the NYSE under the ticker “CEG.”

Bolt Acquisition Corporation

Bolt Acquisition Corporation, which we refer to as Merger Sub, was incorporated in Maryland in April 2011. Merger Sub’s principal executive offices are located at 10 South Dearborn Street, Chicago, Illinois 60603, and its telephone number is 800-483-3220. Merger Sub is a direct wholly-owned subsidiary of Exelon that was formed for the sole purpose of effecting the merger of Merger Sub with and into Constellation. Merger Sub has engaged in no business activities to date and it has no material assets or liabilities of any kind, other than those incident to its formation and those incurred in connection with the merger.

Risk Factors

Before deciding whether to vote for the proposals presented in this joint proxy statement/prospectus, you should carefully consider all of the information contained in or incorporated by reference into this joint proxy statement/prospectus, as well as the specific factors under the heading “Risk Factors” beginning on page 24.

The Merger (see page 47)

Upon completion of the merger, Merger Sub will merge with and into Constellation. Constellation will be the surviving corporation in the merger and will thereby become a wholly-owned subsidiary of Exelon.

In the merger, each outstanding share of Constellation common stock (other than shares owned by Constellation, Exelon or Merger Sub, which shares will be cancelled) will be converted into the right to receive shares of Exelon common stock, with cash to be paid in lieu of fractional shares. The merger agreement provides for an exchange ratio of 0.930 shares of Exelon common stock for each share of Constellation common stock. Exelon shareholders will continue to own their existing shares of Exelon common stock.

Based on the number of shares of Exelon common stock and Constellation common stock outstanding on October 7, 2011, the record date for the two companies’ special meetings of shareholders, existing Exelon shareholders would own approximately 78% of the common stock of Exelon and former Constellation stockholders would own approximately 22% of the common stock of Exelon immediately upon the completion of the merger.

Upon completion of the merger, Mayo A. Shattuck III will become executive chairman of the combined company. Exelon president and chief operating officer Christopher M. Crane will become president and chief executive officer of the combined company. John W. Rowe, the current chief executive officer of Exelon, is expected to retire upon completion of the merger. Upon completion of the merger, Exelon will add to its current 15-member board of directors Mr. Shattuck and three independent directors of Constellation designated by the board of directors of Constellation. By the end of 2012, the board of directors will consist of 16 members, including 12 members who will be designated from the board of directors of Exelon prior to the merger and four from the board of directors of Constellation who will be added to the board of directors of Exelon at the closing of the merger. Exelon’s designees will consist of 11 directors who meet the standards for independence set forth in the NYSE Listing Standards and Mr. Crane, and Constellation’s designees will consist of three directors who meet the standards for independence set forth in the NYSE Listing Standards and Mr. Shattuck. One Exelon director is expected to retire at the end of 2011, and Mr. Rowe is expected to retire upon completion of the merger. Two other current Exelon directors are expected to retire from the Exelon board at the end of 2012.

Following the merger, the resulting company will retain the Exelon name and be headquartered in Chicago. In addition to the corporate headquarters, Illinois will continue to be home to ComEd and Exelon Business Services Company (both in Chicago), as well as the Midwest regional headquarters for Exelon Nuclear (in Warrenville). Pennsylvania will continue to be home to headquarters for PECO (in Philadelphia) and Exelon Power (in Kennett Square). Exelon Nuclear’s headquarters will also be located at Kennett Square. Exelon’s and Constellation’s commercial retail and wholesale businesses will be consolidated under the Constellation brand and headquartered in Baltimore. The combined company’s renewables development headquarters will also be located in Baltimore. BGE will retain its Baltimore headquarters.

Until the merger has received all necessary approvals and is completed, Exelon and Constellation will continue operating as separate entities. The companies are targeting to complete the merger during the first quarter of 2012, subject to receipt of the necessary shareholder and regulatory approvals, although we cannot assure completion by any particular date.

Recommendation of the Board of Exelon (see page 63)

The Exelon board of directors unanimously recommends that the holders of Exelon common stock vote “FOR” the share issuance proposal and the Exelon adjournment proposal.

For a more complete description of Exelon’s reasons for the merger and the recommendation of the Exelon board of directors, see “The Merger—Recommendation of the Board of Directors of Exelon; Exelon’s Reasons for the Merger” beginning on page 63. For a discussion of interests of Exelon’s directors and executive officers in the merger that may be different from, or in addition to, the interests of Exelon’s shareholders generally, see “The Merger—Additional Interests of Exelon Executive Officers and Directors in the Merger,” beginning on page 127.

Recommendation of the Board of Constellation (see page 102)

The Constellation board of directors unanimously recommends that the holders of Constellation common stock vote “FOR” the merger proposal, the compensation proposal and the Constellation adjournment proposal.

For a more complete description of Constellation’s reasons for the merger and the recommendation of the Constellation board of directors, see “The Merger—Recommendation of the Board of Directors of Constellation; Constellation’s Reasons for the Merger” beginning on page 102. For a discussion of interests of Constellation’s directors and executive officers in the merger that may be different from, or in addition to, the interests of Constellation’s shareholders generally, see “The Merger—Additional Interests of Constellation Executive Officers and Directors in the Merger,” beginning on page 128.

Opinions of Financial Advisors

Exelon Financial Advisors (see page 72)

Barclays Capital Inc.

In connection with the merger, Exelon engaged Barclays Capital Inc., or Barclays Capital, to act as a financial advisor to Exelon. On April 27, 2011, at a meeting of the Exelon board of directors held to evaluate the merger, Barclays Capital delivered its oral opinion, subsequently confirmed by delivery of a written opinion, to Exelon’s board of directors that, as of such date and based upon and subject to the qualifications, limitations and assumptions stated in its opinion, the exchange ratio was fair, from a financial point of view, to Exelon.

The full text of Barclays Capital’s written opinion, dated as of April 28, 2011, is attached to this joint proxy statement/prospectus as Annex B. Barclays Capital’s written opinion sets forth, among other things, the assumptions made, procedures followed, factors considered and limitations upon the review undertaken by Barclays Capital in rendering its opinion. You are encouraged to read the opinion and this section carefully and in their entirety. The following is a summary of Barclays Capital’s opinion and the methodology that Barclays Capital used to render its opinion. The summary of Barclays Capital’s written opinion included in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of the opinion. Barclays Capital’s opinion is addressed to the Exelon board of directors (in its capacity as such) for its use in connection with its evaluation of the proposed merger. Barclays Capital’s opinion relates only to the fairness, from a financial point of view, to Exelon of the exchange ratio and does not constitute a recommendation to any shareholder of Exelon or Constellation as to how such shareholder should vote or act with respect to the proposed merger or any other matter.

J.P. Morgan Securities LLC

In connection with the execution of the merger agreement, the Exelon board of directors received an opinion, dated April 27, 2011, from Exelon’s financial advisor, J.P. Morgan Securities LLC, or J.P. Morgan, as to the fairness, from a financial point of view and as of such date, to Exelon of the exchange ratio provided for in the merger agreement.

The full text of the written opinion of J.P. Morgan, dated April 27, 2011, which sets forth, among other things, the assumptions made, procedures followed, matters considered, and qualifications and limitations on the opinion and the review undertaken by J.P. Morgan in connection with rendering its opinion, is attached to this joint proxy statement/prospectus as Annex C and is incorporated by reference herein in its entirety. You are encouraged to read the opinion and the description included in this joint proxy statement/prospectus carefully in their entirety. The summary and the description of the opinion included in this joint proxy statement/prospectus are qualified in their entirety by reference to the full text of the opinion. J.P. Morgan provided its written opinion to the Exelon board of directors (in its capacity as such) in connection with and for purposes of its evaluation of the exchange ratio. J.P. Morgan’s opinion

was limited to the fairness, from a financial point of view, to Exelon of the exchange ratio in the merger agreement and J.P. Morgan expressed no opinion as to any other matter. The opinion does not constitute a recommendation to any shareholder as to how any shareholder should vote with respect to the merger or any other matter.

Evercore Group L.L.C.

In connection with the merger, Evercore Group L.L.C., or Evercore, financial advisor to the Exelon board of directors, rendered its oral opinion, subsequently confirmed by delivery of a written opinion that, as of April 27, 2011 and based upon and subject to the factors, procedures, assumptions, qualifications and limitations set forth in its opinion, the exchange ratio pursuant to the merger agreement was fair, from a financial point of view, to Exelon.

The full text of Evercore’s written opinion, dated as of April 27, 2011, which is attached to this joint proxy statement/prospectus as Annex D, sets forth the assumptions made, procedures followed, matters considered and limitations on the review undertaken. You are urged to read this opinion carefully and in its entirety. Evercore’s opinion was addressed to, and provided for the information and benefit of, the Exelon board of directors (in its capacity as such) in connection with its evaluation of the exchange ratio from a financial point of view and did not address any other aspects or implications of the merger. The opinion does not constitute a recommendation to the Exelon board of directors or to any other persons in respect of the merger, including as to how any holder of shares of Exelon common stock should vote or act in respect of the Exelon stock issuance. Evercore’s opinion does not address the relative merits of the merger as compared to other business or financial strategies that might be available to Exelon, nor does it address the underlying business decision of Exelon to engage in the merger.

Constellation Financial Advisors (see page 110)

Morgan Stanley & Co. LLC

Constellation retained Morgan Stanley & Co. LLC (formerly Morgan Stanley & Co. Incorporated), or Morgan Stanley, to provide it with financial advisory services and a financial opinion in connection with the transaction. Constellation selected Morgan Stanley to act as its financial advisor based on Morgan Stanley’s qualifications, expertise and reputation and its knowledge of the business and affairs of Constellation. At the meeting of the Constellation board of directors on April 27, 2011, Morgan Stanley rendered its oral opinion, subsequently confirmed in writing, that as of such date and based upon and subject to the various assumptions, considerations, qualifications and limitations set forth in its written opinion, the exchange ratio pursuant to the merger agreement was fair, from a financial point of view, to the holders of shares of the Constellation common stock.

The full text of the written opinion of Morgan Stanley, dated April 27, 2011, which discusses, among other things, the assumptions made, procedures followed, matters considered, and qualifications and limitations of the review undertaken by Morgan Stanley in rendering its opinion, is attached to this joint proxy statement/prospectus as Annex E. The summary of the Morgan Stanley fairness opinion provided in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of the opinion. Constellation stockholders are urged to read the opinion carefully and in its entirety. The Morgan Stanley opinion is directed to the Constellation board of directors and addresses only the fairness to the stockholders of Constellation, from a financial point of view, of the exchange ratio pursuant to the merger agreement. The Morgan Stanley opinion does not address any other aspect of the merger and does not constitute a recommendation to any Constellation or Exelon shareholder as to how any such shareholder should vote with respect to the proposed merger or whether to take any other action with respect to the merger. The opinion also does not address the prices at which shares of Constellation common stock or Exelon common stock will trade following the completion of the merger or at any other time.

Goldman, Sachs & Co.

Constellation retained Goldman, Sachs & Co., or Goldman Sachs, to provide it with financial advisory services, including, at Constellation’s request, to undertake a study to enable Goldman Sachs to render an opinion as to the fairness, from a financial point of view, of the consideration to be received in connection with the transaction. Constellation selected Goldman Sachs as its financial advisor because it is an internationally recognized investment banking firm that has substantial experience in transactions similar to the merger. Goldman Sachs delivered its oral opinion, subsequently confirmed in writing, that, as of April 28, 2011 and based upon and subject to the limitations and assumptions set forth therein, the exchange ratio of 0.930 of a share of Exelon common stock to be paid for each share of Constellation common stock pursuant to the merger agreement was fair from a financial point of view to the holders of Constellation common stock.

The full text of the written opinion of Goldman Sachs, dated April 28, 2011, which sets forth the assumptions made, procedures followed, matters considered, qualifications and limitations on the review undertaken in connection with the opinion, is attached to this joint proxy statement/prospectus as Annex F. This summary of the Goldman Sachs opinion provided in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of the written opinion. Constellation stockholders are urged to read the opinion carefully and in its entirety. Goldman Sachs’ advisory services and its opinion were provided for the information and assistance of the board of directors of Constellation in connection with its consideration of the proposed merger and such opinion does not constitute a recommendation as to how any holder of shares of Constellation common stock should vote with respect to such proposed merger or any other matter.

Additional Interests of Exelon Executive Officers and Directors in the Merger (see page 127)

Some of Exelon’s directors and executive officers have financial interests in the merger that may be different from, or in addition to, the interests of Exelon shareholders generally. The Exelon board of directors was aware of and considered these potential interests, among other matters, in evaluating and negotiating the merger agreement and the merger, in approving the merger agreement and in recommending the approval of the share issuance proposal and the Exelon adjournment proposal.

Please see “The Merger—Additional Interests of Exelon Executive Officers and Directors in the Merger” beginning on page 127 for additional information about these interests.

Additional Interests of Constellation Executive Officers and Directors in the Merger (see page 128)

Some of Constellation’s directors and executive officers have financial interests in the merger that may be different from, or in addition to, the interests of Constellation shareholders generally. The Constellation board of directors was aware of and considered these potential interests, among other matters, in evaluating and negotiating the merger agreement and the merger, in approving the merger agreement and in recommending the approval of the merger proposal, the compensation proposal and the Constellation adjournment proposal.

Please see “The Merger—Additional Interests of Constellation Executive Officers and Directors in the Merger” beginning on page 128 for additional information about these interests.

Governance and Management Following Completion of the Merger (see page 133)

Upon completion of the merger, Mayo A. Shattuck III, Constellation’s current chairman, president and chief executive officer, will become executive chairman of the combined company, and Exelon president and chief operating officer Christopher M. Crane will become president and chief executive officer of the combined company. John W. Rowe, the current chief executive officer of Exelon, will retire upon completion of the merger. Upon completion of the merger, Exelon will add to its current 15-member board of directors

Mr. Shattuck and three independent directors of Constellation designated by the board of directors of Constellation. By the end of 2012, the board of directors will consist of 16 members, including 12 members who will be designated from the board of directors of Exelon prior to the merger and four from the board of directors of Constellation who will be added to the board of directors of Exelon at the closing of the merger. Exelon’s designees will consist of 11 directors who meet the standards for independence set forth in the NYSE Listing Standards and Mr. Crane, and Constellation’s designees will consist of three directors who meet the standards for independence set forth in the NYSE Listing Standards and Mr. Shattuck. One Exelon director is expected to retire at the end of 2011, and Mr. Rowe is expected to retire upon completion of the merger. Two other current Exelon directors are expected to retire from the Exelon board at the end of 2012.

Please see “The Merger—Governance and Management Following Completion of the Merger,” beginning on page 133 for additional information about governance and management following the merger.

The Merger Agreement (see page 146)

We include the merger agreement as Annex A to this joint proxy statement/prospectus. We encourage you to read carefully the merger agreement in its entirety. It is the principal document governing the merger and the other related transactions.

Conditions to the Completion of the Merger (see page 150)

We expect to complete the merger after all of the conditions to the merger in the merger agreement are satisfied or waived, including after Exelon and Constellation receive shareholder approvals at their respective special meetings of shareholders and receive all required regulatory approvals.

The obligation of each of Exelon and Constellation to complete the merger is subject to the satisfaction or waiver of a number of customary conditions, including the following:

Termination of the Merger Agreement (see page 151)

Generally, the merger agreement may be terminated at any time prior to the completion of the merger under the following circumstances:

Termination Fees (see page 152)

Under certain circumstances involving a third-party acquisition proposal, a change in a board of directors’ recommendation of the proposals contained in this joint proxy statement/prospectus or a termination of the merger agreement by the other party due to a breach of the merger agreement, Exelon or Constellation may be required, subject to certain conditions, to pay a termination fee of $800 million, in the case of a termination fee payable by Exelon to Constellation, or a termination fee of $200 million, in the case of a termination fee payable by Constellation to Exelon.

No Solicitation (see page 154)

The merger agreement restricts the ability of either Exelon or Constellation to directly or indirectly, solicit, initiate, knowingly encourage or engage in discussions with a third-party regarding a third-party takeover proposal of Exelon or Constellation, respectively. If, however, either party, as applicable, receives an unsolicited takeover proposal from a third-party that, prior to receipt of its respective shareholder approval required to

complete the merger, such party’s board of directors determines in good faith, after consultation with such party’s financial advisors, constitutes a superior proposal or is reasonably likely to result in a superior proposal, such party may furnish information to the third-party and engage in discussions or negotiations regarding a takeover proposal with the third-party, subject to specified conditions. The board of directors of either Exelon or Constellation may also withhold, withdraw, qualify or modify, or publicly propose to withhold, withdraw, qualify or modify its approval or recommendation of the proposals described in this joint proxy statement/prospectus, subject to certain conditions, if such board first determines in good faith, after consulting with outside counsel, that the failure to take such action would be reasonably likely to result in a breach of the board of directors’ fiduciary duties under applicable law.

Accounting Treatment (see page 138)

Exelon prepares its financial statements in accordance with accounting principles generally accepted in the United States. The merger will be accounted for by applying the acquisition method with Exelon treated as the acquiror.

Material United States Federal Income Tax Consequences of the Merger (see page 134)

It is a condition to the merger that both Exelon and Constellation receive opinions from their respective legal counsel to the effect that, for United States federal income tax purposes, the merger will qualify as a “reorganization” within the meaning of Section 368(a) of the Code. Provided that the merger qualifies as a “reorganization” within the meaning of Section 368(a) of the Code, a Constellation stockholder generally will not recognize gain or loss for United States federal income tax purposes as a result of such stockholder’s Constellation common shares being exchanged in the merger for shares of Exelon, except with respect to the receipt of cash in lieu of a fractional share of Exelon.

The discussion of material United States federal income tax consequences of the merger contained in this joint proxy statement/prospectus is intended to provide only a general summary and is not a complete analysis or description of all potential United States federal income tax consequences of the merger. The discussion does not address tax consequences that may vary with, or are contingent on, individual circumstances. In addition, it does not address the effects of any state, local, non-United States or non-income tax laws.

Constellation stockholders are strongly urged to consult with their tax advisors regarding the tax consequences of the merger to them, including the effects of United States federal, state, local and non-United States tax laws.

For a more complete description of the material United States federal income tax consequences of the merger, please see “The Merger—Material United States Federal Income Tax Consequences of the Merger” beginning on page 134.

Regulatory Matters (see page 140)

To complete the merger, Exelon and Constellation must obtain approvals or consents from, or make filings with, a number of United States federal and state public utility, antitrust and other regulatory authorities. The material United States federal and state approvals, consents and filings include the following:

Exelon and Constellation will also provide information regarding the merger to their other state regulators as applicable and as requested. Finally, the transfer of indirect control over certain Federal Communications Commission, or FCC, licenses for private internal communications held by certain subsidiaries of Constellation will require the approval of the FCC.

Exelon and Constellation have made or intend to make various filings and submissions for the above-mentioned authorizations and approvals. Exelon and Constellation will seek to complete the merger in the first quarter of 2012. Although Exelon and Constellation believe that they will receive the required consents and approvals described above to complete the merger, we cannot give any assurance as to the timing of these consents and approvals or as to Exelon’s and Constellation’s ultimate ability to obtain such consents or approvals (or any additional consents or approvals which may otherwise become necessary). We also cannot ensure that we will obtain such consents or approvals on terms and subject to conditions satisfactory to Exelon and Constellation. Please see “Regulatory Matters,” beginning on page 140, for additional information about these matters.

Legal Proceedings Related to the Merger (see page 137)

Following the announcement of the merger on April 28, 2011, twelve purported Constellation stockholders brought putative class actions relating to the merger in the Circuit Court for Baltimore City, Maryland, which we refer to as the state court, and two purported Constellation stockholders brought separate putative class actions relating to the merger in the United States District Court for the District of Maryland, which we refer to as the federal court. On September 27, 2011, the parties to the consolidated action in the state court and the two actions in the federal court entered into a memorandum of understanding setting forth an agreement in principle regarding a settlement of the actions. Under the agreement, Constellation and Exelon agreed to include in this joint proxy statement/prospectus certain disclosures relating to the merger. The agreement provides that the actions will be dismissed with prejudice and that the members of a putative class of Constellation stockholders will release the defendants from all claims that were or could have been raised in the actions, including all claims relating to the merger. The agreement also provides that the plaintiffs’ counsel may apply to the state court for an award of attorneys’ fees and expenses. The settlement is subject to customary conditions, including, among other things, the execution of definitive settlement papers and approval of the settlement by the state court.

We provide additional information on legal proceedings related to the merger beginning on page 137.

Comparison of Shareholder Rights (see page 177)

Constellation is a Maryland corporation. Exelon is a Pennsylvania corporation. The shares of Exelon common stock that Constellation stockholders will receive in the merger will be shares of a Pennsylvania corporation. Constellation stockholder rights under Maryland law and Exelon shareholder rights under Pennsylvania law are different. In addition, Exelon’s Amended and Restated Articles of Incorporation and its Amended and Restated Bylaws contain provisions that are different from Constellation’s charter as currently in effect, which we refer to as its Charter, and bylaws, as currently in effect, which we refer to as its Bylaws.

For a summary of certain differences between the rights of Exelon shareholders and Constellation stockholders, see “Comparison of Shareholder Rights,” beginning on page 177.

SELECTED HISTORICAL FINANCIAL INFORMATION

The following selected historical financial information is being provided to assist you in your analysis of the financial aspects of the merger. The Exelon annual historical information is derived from the audited consolidated financial statements of Exelon as of and for each of the years in the five-year period ended December 31, 2010. The Constellation annual historical information is derived from the audited consolidated financial statements of Constellation as of and for each of the years in the five-year period ended December 31, 2010. The data as of and for the six months ended June 30, 2011 and 2010 has been derived from unaudited interim financial statements of both Exelon and Constellation and, in the opinion of each company’s management, include all normal and recurring adjustments that are considered necessary for the fair presentation of the results for the interim period. The information is only a summary and should be read in conjunction with each company’s historical consolidated financial statements and related notes contained in the Exelon and Constellation annual reports on Form 10-K for the year ended December 31, 2010 and quarterly reports on Form 10-Q for the period ended June 30, 2011, which have been incorporated by reference into this joint proxy statement/prospectus, as well as other information that has been filed with the SEC. See “Where You Can Find More Information” beginning on page 197 of this joint proxy statement/prospectus for information on where you can obtain copies of this information. The historical results included below and elsewhere in this joint proxy statement/prospectus are not necessarily indicative of the future performance of Exelon, Constellation or the combined company.

Exelon Selected Historical Financial Information

Constellation Selected Historical Financial Information

SELECTED UNAUDITED PRO FORMA COMBINED CONSOLIDATED

FINANCIAL INFORMATION

The merger will be accounted for under the acquisition method of accounting, which means the assets and liabilities of Constellation will be recorded, as of completion of the merger, at their respective fair values and added to those of Exelon. For a more detailed description of the acquisition method of accounting, see “The Merger—Accounting Treatment” beginning on page 138 of this joint proxy statement/prospectus.

We have presented below selected unaudited pro forma combined consolidated financial information that reflects the acquisition method of accounting and gives effect to the merger, in the case of the statement of operations information, as though the merger had occurred as of January 1, 2010 and, in the case of the balance sheet information, as though the merger had occurred as of June 30, 2011.

The unaudited pro forma combined consolidated financial information has been prepared giving effect to the issuance of 0.930 shares of Exelon common stock in exchange for each share of Constellation common stock.

The unaudited pro forma combined consolidated financial information would have been different had the companies actually been combined as of January 1, 2010. For example, the selected unaudited pro forma combined consolidated financial information does not reflect cost savings that may result from the merger. The combined pro forma financial information has been presented for illustrative purposes only and is not necessarily indicative of results of operations and financial position that would have been achieved had the pro forma events taken place on the dates indicated, or of the future consolidated results of operations or of the financial position of the combined company. The following selected unaudited pro forma combined consolidated financial information has been derived from, and should be read in conjunction with, the Unaudited Pro Forma Condensed Combined Consolidated Financial Statements and related notes beginning on page 163 of this joint proxy statement/prospectus.

Selected Unaudited Pro Forma Consolidated Financial Information