The average cost of the top 10 deals rose on 7 September was £784, but had risen to £839 by 7 November, an analysis of MoneySuperMarket data representative of the whole market found.
Stephen Murray, energy expert at MoneySuperMarket, said:
Against a backdrop of rising wholesale energy costs, energy prices are on the up and customers are the ones footing the bill.
The speed at which prices are going up is staggering, with a number of suppliers withdrawing their cheapest tariffs since the start of September and this is only going to continue.
As well as a general price rise, the difference between the Big Six standard tariffs and the cheapest deals was also narrowing, according to MoneySuperMarket, which could be a sign "of an impending price hike to the millions of customers on these standard variable deals".