Prime Minister Jacinda Ardern claims NZ consumers are being fleeced by petrol prices. (Video first published in October 2018)

The Government will rush through changes to the Commerce Act to allow the competition watchdog to investigate the margins on fuel, as the pump price hits a record high.

Prime Minister Jacinda Ardern announced the move at her post-cabinet press conference, saying consumers were being "fleeced" at the pump.

The previously-announced legislation will be passed in the first two weeks of sitting in late-October. Prime Minister Jacinda Ardern will then nominate that the retail fuel industry is the first to be investigated by the Commerce Commission.

KEVIN STENT/STUFF Commerce Minister Kris Faafoi, Prime Minister Jacinda Ardern and Energy Minister Megan Woods announce the Government will rush through changes to the Commerce Act to allow the competition watchdog to investigate the margins on fuel, as the pump price hits a record high.

"The study I anticipate will report back next year and I will prioritise a response to it," Ardern said.

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"I am hugely concerned at the level of price that consumers are currently paying at the pump for fuel."

"In 2008 we had one of the lowest pre-tax costs for fuel in the OECD. Today we have the highest in the OECD."

Ardern said the importer margin on petrol climbed from 7 per cent of the price of petrol in 2008 to 16 per cent in early 2018.

"That increase represents a transfer of wealth from petrol consumers to producers to the tune of hundreds of millions of dollars a year," Ardern said.

Strategies to spend less on petrol require effort.

"Consumers, in my book, are being fleeced."

While the Government was already progressing plans to change the Commerce Act to allow market studies, the legislation was not expected to be completed until late this year or possibly in 2019, and there was no certainty that retail fuels would be the first industry selected.

The former National-led Government ordered the Ministry of Business, Innovation and Employment to conduct a study into petrol prices, however two companies - Mobil and Gull - refused to hand over the requested information. Once the law is changed, those companies would be compelled to do so.

GLENN JEFFREY/STUFF A low Kiwi dollar has contributed to very high petrol prices.

AA spokesman Mark Stockdale said the sharp increase in petrol prices this year had left some motorists angry, and the Government appeared to be listening.

"This is welcome news. There's obviously a lot of frustration amongst New Zealanders about the ever increasing fuel prices that we're experiencing now," Stockdale said.

"Motorists are getting quite angry and they're wanting something done about it, and this shows that the Government is listening and fast tracking that legislation."

National leader Simon Bridges described the move as "yet another inquiry" and called on the Government to axe its fuel tax increases.

"She's saying consumers are being 'fleeced' while her Government is driving up fuel prices and taking hundreds of dollars from Kiwi households through higher taxes on fuel."

Bridges added that "National supports another look at the practices of fuel companies".

Although National considered giving the Commerce Commission the powers to conduct market studies, it never did so.

Z Energy, which also supplies the Caltex network, has said repeatedly that it supports the Commerce Commission having greater powers to conduct market studies.

"We are supportive of a Commerce Commission market study that will take the time to fully study the market," a spokeswoman for Z Energy said in Friday.

"It's important to us to have an objective agency who can compel data, with people who have the skills and knowledge to interpret that data and do the work."

On Monday, a spokeswoman rejected the Prime Minister's claim that motorists were being fleeced.

"We would disagree with that, but we think the market study is the best way to establish that."

Shares in the company are down 1.3 per cent on Monday.

RECORD HIGH PRICES

A low NZ dollar has seen record high petrol prices in recent weeks, with prices for 91 octane averaging $2.41 in September. As excise tax increase on September 30 was followed by a 4c a litre increase on Thursday, taking the pump price in Wellington and much of the South Island to $2.489.

This has resulted in a lot of anger from consumers, with 15,000 Facebook users "attending" a planned nationwide petrol strike on October 26.

National have argued that the Government's regional fuel tax in Auckland and smaller excise tax boost nationwide are driving the price surge.

That nationwide tax hike added 4c a litre while the regional fuel tax comes out at 11.5c a litre. Ardern noted that the price of fuel had gone up by about 34c over the last year - well above what could be explained by the tax hikes.

National have promised to repeal the regional fuel tax if elected in 2020.

National party leader Simon Bridges, a former Transport minister, told Ardern she should respond to high prices by cancelling the two tax hikes.

"Petrol companies are no saints but [Jacinda Ardern] trying to blame them for current petrol price hikes is real pot calling kettle black stuff when it's her petrol taxes doing the most damage," Bridges tweeted.

"The importer margin, the profit petrol companies make on every litre of fuel sold and which the Prime Minister wants more information on, is 31 cents per litre and around the same as it was last year. The amount the Government makes is $1.25 - and that keeps increasing," Bridges said in a statement.

"There are a number of other reasons behind record petrol prices and National supports another look at the practices of fuel companies, something we also looked at in Government, but the Government should also be looking in the mirror."

The Government has put the blame on petrol companies, releasing data showing price margins have climbed significantly since 2008.

Figures provided to media by MBIE suggest the margins to fuel companies have more than doubled since 2008, although in January were still below where they were in January 2015.

While getting the legislation passed would be a priority, it would likely not require the use of urgency, Ardern said.

ACC said in late September it wanted to increase its levy on petrol by 1.9 cents a litre and raise the average annual levy on car registrations from $113.94 to $127.68 a year.

ACC Minister Iain Lees-Galloway has been openly sceptical of that proposal, but Ardern said it had not yet been discussed at Cabinet.

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