Z Energy says petrol prices over $2 a litre pushed down industry fuel volumes in the six months to the end of September but the company has expanded its market share.
Chief executive Mike Bennetts said margins were up slightly on the same period last year but so were underlying costs.
Earnings before interest, taxation, depreciation, amortisation and financial instruments (ebitdaf) of $88.7 million were down from $97.3 million in the previous year.
"Petrol and diesel volumes across the industry are down 1.4 per cent on the same period in 2010. In contrast Z's total petrol and diesel volumes have risen 3.4 per cent on the previous corresponding period, meaning that in a tough, competitive market, Z continues to gain market share and grow its customer base."
Volumes remained down in the first part of this six-month period.
The economic outlook for the remainder of the financial year was uncertain and if challenging trading conditions persisted, Z's ebitdaf was likely to be at the lower end of the previously indicated range of $170 million to $190 million.
The company, owned by Infratil and the NZ Superannuation Fund, is converting Shell stations to Z-branded stations in a $60 million project over the next nine months.