Constellation Energy's (CEG) planned acquisition of Calpine is expected to generate more than $25 billion in gains for Energy Capital Partners and its co-investors, The Wall Street Journal reported Monday, citing sources familiar with the matter.

Around $18 billion of those gains will be in Constellation stock, which Energy Capital Partners will have to sell gradually to fully realize its return, the report added.

Energy Capital acquired the natural-gas power producer Calpine for $5.6 billion 2017. The sale to Constellation Energy is expected to close within the next month, the Journal report said.

Calpine, Energy Capital Partners, and Constellation Energy did not immediately respond to MT Newswires' requests for comment.

(Market Chatter news is derived from conversations with market professionals globally. This information is believed to be from reliable sources but may include rumor and speculation. Accuracy is not guaranteed.)

Price: 357.85, Change: +2.45, Percent Change: +0.69