Energy company Npower is to raise gas prices by 15.7% and electricity prices by 7.2% from 1 October, it has said.
The supplier, owned by RWE, is the fifth of the "big six" energy firms to announce increases in UK domestic bills in recent weeks - only EDF has not.
Npower blamed the "volatile global wholesale market" - which it expects to rise in the future - for the change.
But consumer association Which? said customers would question the need for the increase given the firm's profits.
Npower said customers with a dual fuel tariff would see prices rise by 12.2% from October.
"I know it hurts everyone when we put up prices and I wish we did not have to," said Kevin Miles, of Npower.
"Although our half year profits were better than last year they do not begin to match the billions of pounds we are investing in energy for the future.
"With reduced quantities of North Sea gas, we are now forced to buy energy on the volatile global wholesale market. World events have pushed up prices and we believe this trend will continue."
But Richard Lloyd, chief executive of the consumers' association Which?, said that healthy profits would lead customers to question why price rises were needed.
"The Bank of England has predicted that rising utility bills will drive inflation to 5% by the end of the year, which will put more pressure on already squeezed households," he said.
"It is critical that Npower and all suppliers do more to help customers cut their energy bills - whether that is by getting onto the cheapest tariff or making their homes more energy efficient."