New figures show at least 40,000 litres of oil has been spilt in the waters around New Zealand since the Rena disaster in 2011.
The worst year has been 2012, when there were nine spills of more than 1,000 litres each, but Rena alone leaked 350,000.
Maritime NZ received reports of 39,000 litres of spilt oil between October 2011 and August last year, and in April this year, another 1500 litres leaked from a Mobil pipeline in Tauranga.
Maritime New Zealand general manager Nigel Clifford said the figures were not surprising, given the level of marine activity.
"If we look at how we compare to the rest of the world, our statistics are quite low. But we are a maritime nation so there is a lot of activity. So, regrettably, you would expect there ot be the occasional accident. But you have to remember the volume of activity that is going on."
He said the agency was always concerned with oil spills, but these figures were no worse than they were before the Rena disaster.