The National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) is officially behind schedule for its assessment of BP’s plan to drill oil exploration wells in the Great Australian Bight.

But some say the time taken is not the problem - the lack of transparency is.

BP submitted environmental assessments of its plan to drill four deep-water exploratory wells to NOPSEMA at the start of October.

The oil giant was meant to get a response by November, but that deadline has passed.

It is a blow to the project BP wanted to have up and running early next year.

NOPSEMA’s head of regulatory support, Karl Heiden, has told ABC reporters that the assessment team needs more time.

“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.”

It is understood that one hitch may be in BP’s plan to manage the risk of an oil spill.

Mr Heiden did not comment on spills specifically, but did say that the complexity and size of the submission combined with a “significant level of community interest”, were behind the holdup.

“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.”

Meanwhile, the Wilderness Society wants BP's environmental plan for drilling to be made public.

Additionally, Independent senator Nick Xenophon has called for reforms that would allow the federal Environment Minister to have the final say on such major drilling projects.