Z Energy said it expects petrol prices to rise by about 6 or 7 cents a litre, based on the immediate spot price reaction to the weekend attack on a Saudi Arabia oil facility, but said a $3 a litre pump price was "very, very unlikely".

Chief executive Mike Bennetts said in a conference call that Brent crude oil had rallied by 12 to 13 per cent, or US$6 to $7 a barrel, in response to the drone attacks on Abqaiq - the world's largest oil processing facility.

"That would flow through to a price increase of 6 to 7c a litre if it was to sustain," he said.

"The Saudis are confident that that one third of the lost production should be on stream very quickly," he said.

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He noted that President Donald Trump had said the US would tap in it its vast strategic oil reserves to moderate any price increases resulting from the attack.

Bennetts said it was now a matter of waiting to hear what the Saudis say what will happen to the remaining two thirds of capacity affected by the attack.

"It's not clear what will be done - whether it's a week's work or whether it's prolonged absence," he said.

"It's more bad news for us in terms of what that means, but it's not of a scale that would significantly disrupt demand or significantly stress us out in terms of our working capital facility or anything like that," he said.

As to one commentator 's comment that the attack could lead to a $3 litre petrol price at the pump, Bennetts said: " We think that that is very, very unlikely," he said.

Today's conference call, which was convened to discuss Z Energy's submission to the Commerce Commission's recent report on petrol pricing, which was highly critical of the fuel companies.

Z Energy, in its submission, questioned the Commerce Commission's arithmetic, use of economic concepts and choice of the formula it used to conclude the New Zealand transport fuel sector is uncompetitive.

"Z has discovered a number of inaccuracies in the draft findings on profitability, including a misrepresentation of Z's 2016-2018 rate of return as about 22 per cent, around double Z's independently reviewed calculations of about 11 per cent," Bennetts said.

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Bennetts said the Commerce Commission's report had "material inaccuracies that need to be rectified".

The study had also used the wrong number of shares that Z had on issue, inflating the company's market value by $181.5 million, had ignored $158 million of goodwill booked at the time Z bought the Caltex fuel distribution business from Chevron NZ, used the wrong concept for assessing depreciation, and a deferred tax liability had been accounted for in a way unsupported by the relevant literature.

A policy advisory firm, Incenta, also argued the commission's use of a formula known as 'Tobin's q' to calculate the level of competition in the New Zealand fuel distribution sector was "volatile and not appropriate to use as a benchmark".

Z's submission recommended that petrol stations all move to "fully display" all prices, including premium and post-discounts, on price boards.

It also favours opening up wholesale market arrangements - a key commission recommendation - through the use of so-called 'terminal gate pricing', limiting wholesale contracts with distributors to seven years, and establishing an industry code for the retail fuels market that "sets clear rules".

-- With BusinessDesk