Millions of customers of Scottish and Southern Energy face higher bills from September after the group became the third of the major suppliers to raise prices.
The group is to increase gas prices by an average of 18% and electricity prices by 11% from September 14.
The increase will mean a typical annual dual-fuel bill will rise from £1,094 at present to £1,265, an increase of £171.
Scottish Power and British Gas have already announced price hikes and like its rivals Scottish and Southern, which owns Southern Electric, Swalec and Scottish Hydro, said its decision reflected higher wholesale gas prices, a higher cost of using energy networks and the cost of social and environmental schemes.
SSE, which has 5.2 million household electricity customers and 3.6 million household gas users, added it will not raise prices again for households until August 1, 2012.