Genesis Energy is putting up the price of gas throughout the North Island by 5.4% in December.
Earlier this year it increased its daily fixed charge, but is now raising the price for the actual gas used.
Genesis says it last raised the variable price in 2009 and the cost of supplying gas has risen so it needs to pass on some of these increases.
Energy watchdog the Domestic Energy Users Network says unlike electricity there is no independent regulator for gas prices.
Spokesperson Molly Melhuish says Genesis will use any excuse to raise prices including maintaining a reasonable return for its shareholder, the Crown.
