npower has become the third of the Big Six energy companies to announce price hikes during the past fortnight.
npower said it will increase electricity prices by 9.3% and gas by 11.1% from 1 December 2013, meaning its dual-fuel bill will increase by 10.4% overall.
The increases will take the average npower dual-fuel bill to a total of £1,459 a year, up by £137.
Less than two weeks ago energy firm SSE announced it would be raising prices by 8.2% from November 15.
It was swiftly followed by British Gas, which announced on Thursday it would raise prices by 9.2% (10.4% for electricity and 8.4% for gas) from November 23.
British Gas was subsequently struck by a social media disaster, after it launched a misguided Twitter campaign on the same day it announced the rises.
We had a bit of a #LOL at this in our piece When a British Gas Twitter campaign goes wrong: Funniest #AskBG tweets.
There have as yet been no winter price announcements from Scottish Power, E.ON or EDF Energy.