The Private-equity giant, Blackstone Group LP has agreed to purchase the Houston power company, Dynegy Inc. for about $542 million in deal with Princeton-based NRG Energy Inc.

Under the deal, Blackstone will sold nearly one-third of Dynegy's generation capacity or four power plants with 3,884 MW power generating capacity to NRG for $1.36 billion in cash.

Three power plants are located in California and one is located in Maine.

Beside this, NRG will also acquire 1,279-MW Cottonwood Generating Station in east Texas from Kelson Limited Partnership for $525 million.

Out of five plants, four plants use natural-gas whereas one small California plant uses oil.

It is considered to the biggest purchase of Blackstone since 2007 when it announced its $25.1 billion buyout of Hilton Hotels.

The Dynegy's equity is valued at $4.50 a share.

The shares of Dynegy have increased by 59 percent to $4.42 whereas shares of both Blackstone and NRG have declined.

Dynegy has also sold its nine plants at the end of previous year.

Due to weak power prices, the companies are searching for the opportunities to acquire power plants at cheap rates.