The average Bay of Plenty power bill jumped $83.14 in the last year, a 3.6 per cent increase above the national average.
The study, which relied on Electricity Authority data, was based on an average household using 8000kWh per annum - close to the nationwide average residential consumption. The results were compiled by online power retailer Powershop.
Trustpower community relations manager Graeme Purches said the figures were "a load of rubbish".
The way the data was calculated wasn't designed to compare regions, but provided an overall picture.
"Trying to do a calculation based on an average household consumption ... provides a wildly distorted picture."
The calculations also didn't account for special deals and discounts many companies offered, he said.
"The prices quoted, there'd be very few, if any, customers on them. There are only 5 per cent of our customers on standard pricing."
Trustpower prices were not nearly as expensive as they seemed, but were "middle of the road", he said.
About 70 per cent of its customers were locked into fixed contracts, he said.
Powershop's Ari Sargent said there were several reasons customers didn't switch to cheaper suppliers, including being locked into a fixed contract.
"There are also many customers who are still unaware they can save a considerable amount of money by switching, despite the Government's 'What's my number?' campaign over the last few years," he said.
"Some customers sticking with the most expensive retailer are overpaying by more than $650 a year, that's enough to pay for the Christmas spread and most of your presents."
Large retailers were the most expensive in 37 of the 45 regions, where there was less competition from smaller players.
As new entrants pushed into the regions, more customers were expected to switch to a better deal, Mr Sargent said.
