New Zealand oil reserves are below the minimum required by the International Energy Agency (IEA) because of discrepancies in its record system, the government said on Thursday.
A review and recalculation of reserves had shown stocks for 60 days of consumption instead of the required 90 days, Energy Minister Pete Hodgson said.
"The reporting discrepancy has largely been due to longstanding problems with the quality of the data provided around on-shore stock levels and the way in which stock held off shore, or in transit to, New Zealand was accounted for," he said in a statement.
Declining domestic production, which accounts for around 20 percent, had also been a factor.
Accounting of oil and petroleum products stocks has been made more robust and reliable following the review, Hodgson said.
Oil companies operating in New Zealand were being consulted on the best way to increase stocks to the required minimum level in a timely manner. Legislation already existed to pass regulations requiring oil companies to maintain 90 days of reserves.