Constellation is buying natural gas and geothermal power provider Calpine for $16.4 billion, joining together two of the country's biggest power companies. The acquisition would create the nation’s leading retail electric supplier,

Constellation Energy is nearing a roughly $30 billion deal to acquire power producer Calpine, people familiar with the matter said on Wednesday, a move that would significantly expand Constellation's generation assets at a time of rising U.

Separately, Calpine and Constellation are already among the largest power generation companies in the country.