Greenpeace is critical of the granting of approval to Anadarko, an oil and gas company, to test-drill off the Taranaki and Canterbury coasts.
Maritime New Zealand has approved the American company's discharge management plan, which reveals how it would deal with a spill.
The Official Information Act prevents the details being released for now.
A Greenpeace says the public should have been consulted and the Government and Anadarko should release the plan.
The organisation has lodged an Official Information request, but it doubts anything will be released.
It has previously produced modelling that it says shows the consequences would be widespread if deepsea oil-drilling goes wrong off the coast of New Zealand.
But Anadarko spokesperson, Alan Seay says that assumes nothing would be done to prevent the oil's spread.