The company was widely expected to raise the price of its fuel bills after British Gas, Scottish and Southern Energy and Scottish Power announced hikes.
Like those three, E.ON has blamed soaring wholesale prices for the rises.
The average dual fuel bill will rise by about 15% for E.ON customers after the price increase in September. Gas will go up by 18.1% and electricity by 11.4%.
Existing E.ON customers have been offered some respite from the rises - it has announced current customers will have their prices frozen for two years.
Graham Bartlett, director of E.ON, explained: "I know that this is hard for customers and want to help them avoid future price volatility, which is why we've launched our new two-year fixed price deal."
The Consumer Focus group has questioned the need for such severe price rises across the board, claiming wholesale energy prices were actually higher in 2008 than they are now.
The Mirror quotes chief executive Mike O'Connor as saying: "Customers will feel they didn't get the benefit when wholesale costs were low. Wholesale costs are around a third lower than their 2008 peak yet consumer prices have reached an all-time high."
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