New York - Giant energy company Exelon Corp, the country's largest utility, has made an uninvited bid to acquire NRG Energy Inc for 6.2 billion dollars, following billionaire investor Warren Buffett's example of buying into the market amidst the slump.

NRG is the second-largest power producer in Texas, and would give the Chicago-based Exelon capacity outside its Illinois and Pennsylvania operating bases, Bloomberg financial news service reported. NRG's shares lost half its market value in two months.

Last month, Buffet's MidAmerican Energy Holdings Co moved to buy Constellation Energy Group Inc for 4.7 billion dollars, less than half the company's market capitalization from the week earlier.

Buffett last week urged investors to make use of bargains available after the market plunge of recent weeks that followed the collapse of the housing bubble, US government rescue efforts of individual companies and the government's 700-billion-dollar commitment to buy up soured mortgage assets and bank shares.

NRG and Exelon have proposed 24 new nuclear reactors to boost power generation with low carbon emissions.