Prices were being kept high by a lack of competition that allowed fuel sellers to possibly earn close to $400 million a year in excess returns, a draft report by the Commerce Commission found.
"Our instinct was certainly that New Zealanders were being fleeced at the pump, now the Commerce Commission has confirmed that," Ardern said.
"I can tell New Zealanders we cannot stand by as they are facing that pressure at the pump and while they are being fleeced."