As New Zealand's first ever Commerce Commission inquiry into the retail fuel market kicks off, Winston Peters says the Government won't be afraid to pass laws restricting "profiteering" if that's where the findings lead.
He also said the recent drop in petrol prices won't deter a thorough look.
"This is decades old as a problem," the Deputy Prime Minister told TVNZ's Breakfast this morning. "There've been international comparisons of the cost here against other countries in the world, and across the country it's clear that it's not fair. So we're going to do something about it.
"It's not complicated as to what we might do. But first of all let's find out the facts."
The investigation was announced yesterday, with Prime Minister Jacinda Ardern pointing out that petrol profits in New Zealand have more than doubled over the past decade.
"New Zealanders deserve peace of mind that the price they're paying at the pump is fair," Ms Ardern said yesterday.
Mr Peters spent much of his interview this morning demurring when asked repeatedly by Breakfast host Jack Tame for specifics about what the end result of the investigation could entail. But legislation or public embarrassment are both on the table, he eventually acknowledged.
"If we have to legislate we will, or if we have to point out the very obvious to them that may be enough," Mr Peters said. "What it needs is an authoritative body, independent of Government, to lay out the situation for both the industry and consumers."
Mr Peters also suggested "an oversight body that is critically scrutinising month by month the movement of these prices and ensuring that the industry behaves itself".
"It's not complicated. Other countries have done it. So can we," he added.
"We're not into regulation or interference with business in this country, but if the business that we're talking about carries on as we suspect - that is, doubling its profits without any regard to the consumer - then the Government's job is to step in, and step in we will."
About six billion litres of petrol and diesel are consumed for land transport use in New Zealand annually.
The study is set to begin tomorrow, with a final report due next December.