It reports that the 30% rise in wholesale gas prices is pushing energy companies to make bills more expensive.
Npower and E.ON will follow Scottish Power, Scottish and Southern Electricity and British Gas if they announce price rises for fuel bills.
The Independent says both are expected to announce "significant" rises in gas and electricity bills - with most energy customers facing an extra Â£200 or so on their bills.
The Big Six supply gas and electricity to 99% of the UK. The Government wants to shake up the monopoly and is currently investigating the sales techniques, tariff complexity and pricing of many of the bigger firms.
The energy minister Chris Huhne has previously encouraged consumers to use price comparison websites to find cheaper gas and electricity.
But as the price rises kick in across the board, that could be increasingly difficult, warned one consumer group.
The other "Big Six" firm, EDF Energy, has not ruled out price rises either, although its current dual-fuel tariff is fixed in price til September 2012.
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