A plan to drill oil exploration wells in the Great Australian Bight is taking longer to assess than first expected.

BP wants to drill four deep-water wells in the Bight from early next year.

It submitted an environmental plan to regulator, the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA), at the start of October and was meant to get a response by the start of November.

But head of regulatory support, Karl Heiden, said the assessment team needed more time to consider the matter.

"The law allows NOPSEMA to take as much time as required to ensure a professional, thorough and rigorous assessment," he said.

"It's a relatively unexplored region so there's a lot of new information about the sensitivities that are in that region."

Part of the assessment is how BP will manage the risk of an oil spill.

Mr Heiden said the extension of time was needed because of the complexity and size of the submission and the "significant level of community interest".

"All of those factors contribute to this particular submission being a complex one, hence the need for NOPSEMA to take a little bit of additional time to conduct the initial screening."

The Wilderness Society has expressed concern BP's environmental plan for drilling has not been made public.

Independent senator Nick Xenophon said he believed the federal Environment Minister needed to have the final say on significant drilling projects.