In connection with the all-stock, tax-free merger, RRI Energy changed its name to GenOn Energy, and each share of RRI stock will become a share of GenOn Energy common stock.

Mirant stockholders will receive a fixed ratio of 2.835 shares of GenOn Energy common stock for each share of Mirant common stock.

GenOn chairman and CEO Edward Muller said that this merger will create significant near-term stockholder value driven by $150m of annual cost savings.

"GenOn’s geographic diversity, scale, financial strength and flexibility leave us well-positioned to deliver additional stockholder value as the power markets recover," Muller said.