The retail fuel market will be the first Commerce Commission market study, New Zealand Prime Minister Jacinda Ardern said on Monday.

"I have previously voiced my concern about the high cost of fuel, because it is a core expense for consumers and businesses," Ardern said in a statement, adding the government is committed to easing financial pressure on families.

"New Zealanders deserve peace of mind that the price they are paying at the pump is fair," the prime minister said, adding, "At the moment we can't definitively say whether that is in fact the case across New Zealand so this is a market that most certainly warrants a full investigation."

Commerce and Consumer Affairs Minister Kris Faafoi said that while there were several possible markets mooted for consideration, the retail fuel market clearly met the test for investigations.

"Simply, it's in the public interest to ensure people and business aren't paying too much for fuel. There are existing indications of competition problems in the retail fuel market that are of concern to me, such as the more than doubling of petrol and diesel importer margins over the past decade," Faafoi said.

It is also a market that is hugely important to consumers and to the economy, given the extent to which people rely on fuel and the size of the market, with around 6 billion liters of petrol and diesel consumed for land transport use annually, he said.

The Commerce Commission will be undertaking a full and thorough analysis into competition in the retail fuel market so as to better understand the market conditions and determine whether consumers' interests are being protected at present, the minister said.