Exelon Corporation (NYSE: EXC) is a giant electricity generating and distributing company headquartered in Chicago. It was created in October, 2000 by the merger of PECO Energy Company, of Philadelphia, and Unicom, of Chicago (which owned Commonwealth Edison).

Exelon has 5.2 million electricity customers and, in Philadelphia, 460,000 natural gas customers.

In June, 2005 Exelon had full or partial ownership of 19 nuclear reactors in 11 nuclear power plants.

On June 30, 2005 the Federal Energy Regulatory Commission approved the merger of Exelon and Public Service Enterprise Group Inc., a New Jersey utility, thus creating the largest utility in the U.S. [1]. This merger will add PSEG's 2 million electric and 1.6 million natural gas customers, and will add 1 more reactor to Exelon, for a total of 20. The merger is set to be completed in the second quarter of 2006, at which time the name of the company will change to Exelon Electric & Gas.