RWE has hired Goldman Sachs to consider the future of Npower. One of the options includes selling the business, according to a report this weekend.
Npower was purchased by RWE in 2002 for £3.1bn. It employs over 11,000 staff in the UK and supplies energy to 6.8 million homes.
Last year, Npower signed a £21m three-year sponsorship of the Football League.
RWE is thought to be considering a sale to pay down its debt.
The possible sale would attract the attentions of rivals. Scottish power-owner Iberdrola is believed to be a potential buyer.
A spokesperson for Npower said the company did not comment on market speculation.