The head of Refining New Zealand says 2015 was a "remarkable" year, with crude oil cheap and strong demand for petrol.

The head of New Zealand's fuel refinery says motorists are keeping petrol prices high, as he denied the company is rorting customers.

On Wednesday the Refining New Zealand which owns the fuel refinery at Marsden Point, reported a 1400 per cent increase in profits over 2014, at $150.7 million.

The boom was driven by a massive jump in margins, with the price of oil plunging to the lowest level in over a decade in recent weeks, at around US$30 a barrel.

Meanwhile petrol prices are only at 12 month lows. The "national price" of regular petrol - a term used for company-owned petrol stations in most areas without regional discounting - is currently $1.739, the sale level at February 2015.

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This meant the refinery's gross margin rose to more than US$9 a barrel, up from less than US$5 in 2014.

Chief executive Sjoerd Post said the company was in "manufacturing nirvana". While crude oil - its raw product - had plunged in price, falling petrol prices had led to a rise in demand for gasoline from consumers, so its selling price was relatively stable.

Motorists were driving the strong margins, Post said, and the company was not rorting consumers.

"It all starts with individuals like you and me waking up and looking at the pump price and saying 'I'm going to drive more'," Post said.

Sales of SUVs in the United State were "soaring" Post said, while he understood sales were also strong in New Zealand, keeping demand for fuel strong.

"I live in Auckland. Everybody is driving a [Toyota] Prado or better. I've got a BMW X5...It's the consumer making it. If the consumer didn't say 'I like that [pump] price, that wouldn't be happening," Post said.

"We would only be rorting them [motorists] if demand was slumping and we saw at the pump that people couldn't afford it and we were still trying to hold the price up."

For weeks petrol companies have been saying that their margins were not increasing to the degree that oil prices were falling.

The AA has backed the argument, saying the price of refined petrol was US$60 a barrel, twice the price of crude oil.

But in New Zealand the situation is complicated by the fact that three of the major petrol companies, BP, Z Energy and Mobil, collectively own around 53 per cent of NZ Refining. With the company announcing a 20c a share payout, the three companies will share more than $30m in dividends.

AA spokesman Mark Stockdale said the results were "no great surprise" but showed where the benefit of falling oil prices were accruing.

"It's the middle men that are making the money, and motorists aren't benefiting from the low, low oil prices," Stockdale said, adding that privately owned refineries were simply acting in the best interests of their shareholders.

"They're not looking out for motorists, that's for sure."

Stockdale said that while petrol companies had argued that their retail businesses were separate from the investment in the refinery, in recent years when refinery margins were low, petrol companies had needed to "kick in" to help pay for an upgrade at Marsden Point.

Motorists were paying for this upgrade at the pump, Stockdale said, and the AA believed the profits of the refinery should be used to pay for the investment, allowing the retailers to cut the margins through lower pump prices.

On Wednesday Hellaby Holdings, which has a business maintaining refineries, claimed that companies like New Zealand Refining were delaying upgrades to capitalise on the strong profits on offer.

Post denied the company was putting off maintenance, with NZ Refining conducting an essential maintenance shutdown of the most profitable part of the plant in April.

Shares in New Zealand Refining climbed 3.9 per cent to $3.74.