COLUMBUS, Ohio - Exelon Corp. sweetened its hostile takeover bid yesterday for NRG Energy Inc. 12 percent to $8 billion in stock, citing newly identified cost savings along with NRG's recent deal for Reliant Energy Inc.'s Texas retail business.

Exelon chairman and chief executive officer John Rowe called it a "best and final offer." The new bid increases the price for NRG about $1 billion.

"Together, the two companies' shareholders get something very rare, a truly effective combination in an industry in which significant profitable growth is very hard to come by," Rowe said in a conference call.

NRG, of Princeton, N.J., which rejected Exelon's previous bid, said it would review the latest offer.

If NRG combines with Chicago's Exelon, the new company would be the largest U.S. power generator, providing energy to about 45 million homes. Exelon, which owns Philadelphia's Peco Energy Co., is already the nation's largest nuclear-power company.

Rowe told analysts that the deal would further expand Exelon's nuclear fleet.

Exelon would also add gas generation and coal plants, assets that would be valuable even under pending emissions caps, and broaden its footprint in Texas, California, and the Northeast.

Exelon is now offering 0.545 shares of its stock for each NRG share. The old offer had been 0.485 shares.

The new offer represents value of more than $3 billion to NRG shareholders, Exelon said. Exelon said its shareholders would see added value of $1 billion to $3 billion.

The bid was increased after Exelon said it found $1.5 billion more in potential savings from the tie-up, and because of NRG's acquisition of Reliant Energy's retail business in May for $287.5 million.

The new bid is still low, said Jefferies & Co. Inc. analyst Paul Fremont, because it is just a 7 percent premium from NRG's closing stock price Wednesday. Jefferies has a $30 price target for NRG.

NRG shares fell $1.25, or 4.80 percent, to $24.80 in trading yesterday. Its shares have traded between $14.39 and $43.95 over the last year.

Exelon and NRG have nominated a slate of directors for shareholders to vote on at NRG's annual meeting July 21. The outcome of that vote could determine whether the sale happens.

Rowe told analysts that Exelon would sell assets and issue stock to reduce the debt of the combined company.

Last month, Exelon said it would lay off 500 employees and take a $40 million severance charge in the second quarter as part of a massive cost-cutting program totaling $350 million.

Exelon shares fell $2.19 to close at $49.37. Its shares have traded between $38.41 and $92.13 in the last year.