Wellington-headquartered Contact yesterday announced the price hikes, for residential and business customers, with general trading manager Steve Cross saying the increases reflected the significant upwards trend in wholesale gas prices.
Transmission costs associated with the NGC-owned high-pressure pipeline network had also increased.
"These are costs beyond Contact's control. The Maui gas field has historically been the source of a cheap gas supply for New Zealand, by international standards. But Maui is drawing to the end of its life, and wholesale gas prices are moving upwards to reflect the pressure on supply.
"Contact has to strike a balance between managing the impact of all these increases, and remaining a viable, competitive energy provider in Auckland," Cross said.
An average Auckland residential household could expect to pay an extra $NZ1.24 a week.
Contact shares rose five cents yesterday in reaction to the news to close at $NZ5.33, against last week's record high of $NZ5.60.
Last month government-owned Genesis Power said it was raising residential gas prices by an average of 12.7% from January.