Claims that privately owned power companies charge the highest prices are wrong, the government says.
The Greens have Treasury documents they say confirm energy watchdog Molly Melhuish's research showing a 12 per cent price difference between private and state-owned companies.
Acting Prime Minister Bill English says Treasury's figures have been taken out of context.
"The calculations you are seeing, trying to say SOEs have lower prices, are simply wrong," he told reporters on Tuesday.
"The calculations are meaningless - the market is competitive and no company can consistently have higher prices than another company and the idea that the owners of those companies can decide to do that is just absurd."
Mr English says if SOEs are consistently cheaper there wouldn't be any private companies.
The Greens are using the documents to argue against the partial privatisation of four state-owned energy companies, saying price rises are inevitable.