Consumer groups are asking questions of one of the UK's so-called 'big six' energy providers after it announced a leap in profits despite falling sales.
EDF, which supplies electricity and gas to around 5.5 million residential and business customers, reported underlying earnings of £1.6bn for the UK in 2011.
That is up from £1.4bn the previous year.
However, revenues were down to £7.1bn from £7.7bn as households used less gas over the milder winter.
EDF said underlying earnings were boosted by increased nuclear output and falling wholesale gas prices but consumer groups believed this would confuse customers.
Audrey Gallacher, director of energy at Consumer Focus, said: "This will leave many customers wondering whether energy prices can, and should, be cut further.
"Consumers need to know big profit margins are not being made needlessly at their expense."
EDF cut its gas bills by 5% from February 7 citing a 9% reduction in wholesale costs - having increased bills by 15.4% the previous November.
At the time of the bill reductions, the company's chief executive told Sky News he was committed to fairness.
Vincent de Rivaz said: "What customers want more than anything else is fair, clear and transparent prices.
"We know they want action rather than words, that is why we are the first major supplier to announce a cut and were the last to increase prices."
In response to the figures, Which? executive director Richard Lloyd said: "The energy companies must raise their game and demonstrate their commitment to giving consumers the best price for their energy.
"If they do, it could be the start of a better relationship with their customers."
The results come a week before British Gas publishes its own set of annual figures.
A 25% drop in profits to £550m is expected.
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