NRG Energy shares surged nearly 25% to lead the S&P 500 on Monday after the firm delivered better-than-expected first-quarter results. Separately, the company announced a $12 billion acquisition of a power portfolio from LS Power Equity Advisors.

The deal, to acquire a portfolio of natural gas generation facilities from LS Power Equity Advisors, will double NRG’s power-generation capacity, the company says.