Greenpeace is arguing in the High Court that the Environmental Protection Authority failed in its legal responsibilities by allowing Anadarko to drill for oil off the coast of Raglan.
Lawyers for Greenpeace are arguing the EPA failed to meet its legal responsibilities because it didn't see key documents on how an oil spill would be managed.
The authority says it didn't need to see those documents because they were assessed by Maritime New Zealand instead.
But Greenpeace says the authority shouldn't be allowed to delegate its responsibility because Maritime New Zealand doesn't consider environmental damage.
It says allowing drilling to go ahead without seeing those documents breaches international laws relating to polluting the sea.