The refinery's annual gross refining margin averaged $US6.39 a barrel, with the exchange rate at US80 cents.
For the two months to October, the refinery produced seven million barrels, generating a processing fee of $42.5 million.
New Zealand Refining is carrying out a study examining the cost-effectiveness of spending $500 million to replace its aging petrol-making plant at Marsden Point, and lift its market share.
The company's stock have fallen 4 cents to $2.95 a share.
New Zealand Refining is the country's only refinery, supplying about 80% of the country's refined fuels and charging a processing fee for refining crude oils and feedstocks.
The company is 73% owned by BP, Mobil Oil, Caltex, and Z Energy owner Greenstone Energy.