Customers who get their gas and electricity from npower will face higher prices from today.
The energy distributor is set to ask its four million customers to pay up to 15 per cent more on their bills in a move set to spark reciprocal alterations from its rivals.
Today's price hikes come after the major energy providers cut their costs last spring.
Analysts say rising oil costs are contributing to the residential energy price changes, with oil prices going above $100 a barrel in the US this week.
Commenting on the first of what is expected to be a number of price-change announcements, Tim Wolfenden, head of home services at comparison website uSwitch.com said he doubted "anybody will be particularly surprised by this".
"Ever since British Gas and npower announced price increases on their market trackers and npower followed this up with a price hike on its online plan, it has been clear that prices are going to be heading north again," he said.
Mr Wolfenden added: "And once one of the suppliers makes this move it will give competitors the green light to go ahead with price increases of their own. This speculation could rapidly turn into price rise misery for consumers in 2008."
Adam Scorer of energy watchdog Energywatch said he expects npower customers to be "despondent" and those of the other energy companies to be "looking over their shoulders to see how they respond".
"It's a pretty bleak picture in 2008," he added.
British Gas and npower had previously announced price increases on their market trackers and npower upped its online tariff for new customers by 13 per cent at the end of last month.