The net purchase price of the deal is roughly $26.6 billion, which includes the assumption of debt for the privately held Calpine. Constellation Energy rose 9.5% to $266.89 in pre

Constellation is buying power natural gas and geothermal power provider Calpine in a cash-and-stock deal valued at approximately $16.4 billion, joining together two of the country’s biggest power companies.

Constellation Energy Corp. agreed to acquire closely held Calpine Corp. for $16.4 billion to add scores of power generation assets across the US as the nation’s electricity demand is forecast to surge.