|Subsidiary of Exelon|
|Founded||1816 (as the Gas Light Company of Baltimore, later the Consolidated Gas Light, Electric Power Company of Baltimore City)|
|Headquarters||Baltimore, Maryland, U.S.|
|Mayo A. Shattuck III
(Former President and CEO)
|Products||Electricity, Natural gas|
|Revenue||$13.76 billion (2011)|
Constellation Energy Group (former NYSE ticker symbol CEG), headquartered in Baltimore, Maryland, was an energy producer, trader, and distributor. The company operated over 35 power plants in 11 states (mainly Maryland, Pennsylvania, New York, West Virginia, and California) under its operating and holding company Constellation Energy Group. Constellation Energy's regulated utility, Baltimore Gas and Electric Company, operated in central Maryland. Constellation Energy was a Fortune 500 company and was one of the top electricity producers in the United States.
In April 2011, Exelon of Chicago announced its intention to purchase Constellation Energy. The acquisition was approved by FERC and the companies officially combined on March 12, 2012 with Constellation Energy taking the Exelon name and the corporate headquarters moving to Exelon in Chicago, Illinois. Before its departure, Constellation Energy was the only remaining Fortune 500 company headquartered in Baltimore. The competitive and wholesale energy supply business of Constellation Energy would become a subsidiary of Exelon re-branded as "Constellation, an Exelon company." Baltimore Gas and Electric, formerly the regulated utility of Constellation Energy, would become a regulated utility operating under Exelon Utilities.
Constellation Energy, with 2007 revenues of $21 billion, was the nation's largest competitive supplier of electricity to large commercial and industrial customers and the nation's largest wholesale power seller.
Constellation NewEnergy, a wholly owned subsidiary of Constellation Energy, was a leading competitive supplier of electricity, natural gas, and energy-related services to commercial, industrial, and institutional customers throughout North America. Constellation NewEnergy served more than 19,000 customers throughout 31 states and three Canadian provinces, representing nearly 8,000 megawatts of peak load and more than 354 billion cubic feet (1.00×1010 m3) of annual natural gas consumption.
Constellation Generation Group owned approximately 9,000 MW of generating capacity from power and fuel processing facilities in seven states and generated more than 52 million MW-hours per year. Its generation portfolio included plants powered by nuclear, coal, natural gas, oil and renewable fuels. 
Constellation Commodities Group conducted energy trading operations by trading a diverse portfolio of electricity, natural gas, and other energy products under both short- and long-term contracts to energy users, including utilities and other energy marketers.
Constellation Energy's regulated utility, Baltimore Gas & Electric Company or BG&E, (later shortened further to BGE) delivered electricity and natural gas to approximately 1.2 million customers in the central Maryland region.
Constellation Energy employed almost 10,000 people. It was named "2004 Energy Company of the Year" in the Platts Global Energy Awards, and was chosen by its peers as the best in the energy industry when it was awarded Most Admired Energy Company of 2004.
Joint ventures and acquisitions
On September 15, 2005, Constellation Energy announced a new joint venture, UniStar Nuclear, with Areva to market the European Pressurized Reactor (EPR) in the USA. Constellation Energy had withdrawn its Lusby, Maryland, and Oswego, New York, sites from the NuStart consortium finalist list. However, both sites desire new nuclear units (see Nuclear Power 2010 Program).
On December 19, 2005, FPL Group, Inc. (owner of Florida Power and Light Company in Jacksonville) announced the acquisition of Constellation Energy in a merger transaction valued at more than US$11 billion as well as the fact that it would adopt "Constellation Energy" as its name for the post-merger entity. The merger was canceled on 25 October 2006.
After Constellation Energy was reported to have had exposure to Lehman Brothers, following that investment banking firm's bankruptcy filing, following the "Great Recession" of late 2008, Constellation's stock went down 56% in the first day of trading having started at $67.87. The massive drop in stocks led to the New York Stock Exchange halting trade of Constellation. The next day, as the stock plummeted as low as $13 a share, the company announced it was hiring Morgan Stanley and UBS to advise it on "strategic alternatives" suggesting a buyout. While French power company Electricite de France, who already owned 9.5% of Constellation's shares, bid for the company, Constellation ultimately agreed to a buyout by MidAmerican Energy, part of billionaire Warren Buffett's Berkshire Hathaway company. On December 17, 2008, Constellation Energy has canceled its merger with Berkshire Hathaway, instead opting to sell its nuclear energy assets to EDF.
In April 2010, Constellation Energy has closed its agreement with Clipper Windpower to acquire the Criterion Wind Project in Garrett County, Maryland, and to purchase 28 Clipper Liberty 2.5MW wind turbines for the project. Construction of the project was completed in December 2010.
On April 28, 2011, Exelon Corporation (which was a merger of Unicom, the former Commonwealth Edison electric utility in Chicago, Illinois, founded 1907; and PECO, the former Philadelphia Electric Company in Pennsylvania, founded 1881) announced its intention to purchase Constellation Energy which was completed on March 12, 2012. As a result of the acquisition, Exelon would take ownership of Constellation's assets and business units.
Part of the archives of the Baltimore Gas & Electric Company and the former Consolidated Gas Light, Electric Power Company of Baltimore City and its ancient predecessor, the Gas Light Company of Baltimore are held by the Baltimore Museum of Industry on Key Highway on the southeastern end of the Inner Harbor. The Baltimore Gas & Electric Company's photographic collection consists of approximately 250,000 photographic prints and negatives, in more than 50,000 series. (http://www.thebmi.org/page/image_database)
- Calvert Cliffs Nuclear Generating Station, on the Chesapeake Bay, Calvert County; Lusby, Maryland
- Conemaugh Generating Station
- Ginna Nuclear Generating Station
- Keystone Generating Station
- Nine Mile Point Nuclear Generating Station
- Safe Harbor Dam, on the Susquehanna River, Pennsylvania
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