Z Energy's share of the petrol market continued to decline in the December quarter although industry margins lifted.
The petrol retailer's report for the three months to December showed its share of total industry fuel volumes fell nearly a percentage point to 29.6% compared with a year earlier.
The company sold 214 million litres of petrol in quarter, down from 227 million in the same three months a year earlier, but lifted diesel sales to 231 million litres from 220 million.
Z Energy spokesman Jonathan Hill said the company's market share is almost exactly where it was when it was purchased from Shell in April 2010 and it had secured a higher margin per litre of petrol sold.
Chief executive Mike Bennetts has said previously his company is not willing to sacrifice margins in order to maintain market share.