Ofgem says the big six energy suppliers saw profit margins in the supply of gas and electricity rise to 4.3% in 2012, up from 2.8% in 2011.
The watchdog says supplier profit per household customer rose to £53 last year, from £30 a year earlier.
Profit margins at the firms fell from 24% in 2011 to 20% in 2012.
Overall, profits in generation and supply across the half-dozen firms fell from £3.9bn in 2011 to £3.7bn in 2012.
The information comes from an analysis by Ofgem of the annual financial statements of the firms Centrica (which owns British Gas), EDF. E.On, Npower. Scottish Power and SSE.