Contact Energy's customer numbers rose slightly in December.
The power firm's monthly operational figures shows it had 443,000 electricity customers at the end of the month, 500 more than at the end of November.
Gas and LPG customer numbers held steady.
Over 2011, Contact lost 21,500 electricity customers, due to government-mandated changes to promote competition, and many players in the electricity market cutting prices to attract users.
Total generation slipped from 811 to 776 gigawatt hours in December, while total electricity purchases rose from 724 to 713 gigawatt hours.