Greenpeace has argued for a ban on offshore drilling in front of a parliamentary select committee, saying the risks are too great.
The environmental group released modelling earlier this week which shows the consequences could be devastating and widespread if deepsea exploratory drilling of the Taranaki and Otago coasts goes wrong.
MPs from Parliament's Local Government and Environment select committee heard the problem with deepsea drilling, which occurs below a depth of 200 metres, is that it is so dynamic.
Greenpeace campaigner Simon Boxer said equipment can easily fail in cold seas when drilling occurs in unknown geology, where oil temperatures and pressure can be very high.
He said industry figures show there were more than 500 blowouts offshore on rigs between 1970 and 2007.
Some 128 of those incidents led to significant environmental damage, he said.
Mr Boxer said while Anadarko, which is planning exploratory drilling from November off the Taranaki coast, has criticised Greenpeace's modelling, Anadarko's own modelling plan has still not been made public.
A Maritime New Zealand spokesperson says Anadarko's oil spill modelling and response plan is still being assessed.