British Gas reveals profits of £270m for the past six months, weeks after announcing plans to raise electricity and gas prices.
Owner Centrica said the figure for its residential division was 54% down on the previous six months and the company had been selling gas at a loss since April due to rising costs on wholesale markets.
Even so, the company is facing public anger after reporting £1.3bn in half-year profits, down 19 per cent on the same period last year.
Centrica chief executive Sam Laidlaw said: "Global events have resulted in a steep increase in commodity prices, with UK wholesale gas prices 30 per cent higher than last winter."
The group makes most of its profit from developing gas and oil fields, operating power stations and trading energy.
British Gas said recently that it would raise gas prices by 18 per cent, and electricity prices by 16 per cent, pushing the average monthly bill for its nine million customers to £101.
Critics have raised doubts over the impact of rising wholesale prices - with independent lobbyist Consumer Focus claiming they remain around a third lower than their 2008 peak.
Energy regulator Ofgem has started an inquiry into how prices are set after stating that tariffs seemed to respond much quicker when wholesale prices went up.
Centrica has frequently defended itself as one of the most transparent suppliers in the market.
It also says it is committed to investing in its energy networks, with more than £15bn of spending pledged for the next decade on nuclear, wind farms and gas-fired generation.
Ofgem has said £200bn of investment is required between now and 2020 to secure Britain's energy supply.