Mighty River Power generated 1785 gigawatt hours of electricity in the three months to the end of June, 27% more than in the same period a year ago.
The increase was mainly due to more geothermal and hydro generation.
Mighty River says sales to residential and commercial customers fell 5%, due to strong competition, the Christchurch earthquake and warmer than usual weather.
The State-owned power company says gas fired generation fell 65% to 33 gigawatt hours, or about 2% of generation, because of lower spot prices and above-average national hydro storage.