The company was spending more on marketing to combat competition, and identified both crude oil supplies and capital recovery charges as risks for the full year result.
However, retail margins improved to 2.6 cents per litre of petrol and diesel sold, compared with 2.4 cents per litre in the same half last year, said Z's chief executive Mike Bennetts said.
"Volume loss will not be recovered as focus is on optimising retail margins, growing non-fuel income and high grading the commercial portfolio, while not eroding integrated value."
Total sales volumes for the year are now estimated to total 2.45 million litres, compared to previous guidance of 2.6 million litres, with competitors taking larger shares of both the petrol and diesel markets over the last six months in an environment of overall decline, reflecting high fuel costs.
The company also expects to save $5 million a year by signing new contracts for supply of petrol and diesel from a Korean refinery, and will release $84 million of capital and a $27 million gain to Z through the sale and leaseback of 44 retail service stations, following an initial eight stations so treated.
Total revenues were also affected by temporary retail outlet closures as the company completed its rebranding exercise, as it shifts from the Shell brand to the indigenous Z brand, reflecting its ownership by Infratil and the New Zealand Superannuation Fund. The result releases a share of earnings for Infratil of $7.9 million, compared with $18.3 million in the same period last year.
Gross margins improved at the Marsden Point oil refinery in the second quarter after a weak first quarter, giving margins for the first half of $7.39 a barrel, above previous guidance of $7 a barrel for the current financial year. However, the outlook remains volatile, with margins likely to fall away in the second half at the refinery, where Z is 17 per cent shareholder.
Crude oil prices for the year as a whole are now expected to average $137 a barrel, the same as last year, compared with a previously expected $156 a barrel, assisted by ongoing strength in the value of the New Zealand dollar.