A decision is looming on a controversial plan to drill for oil in the Great Australian Bight.
International energy company Equinor has exploration rights on a site about 370km off the South Australian coast.
It submitted an environmental plan to federal regulators in April this year but the National Offshore Petroleum Safety and Environmental Management Authority has twice delayed a decision, calling on the company to provide more information.
NOPSEMA's ruling is now due on Thursday, but it could again be postponed amid renewed calls from environmental groups for the exploration plan to be abandoned.
Last week Greenpeace released a report which questioned what it said were plans by the Norwegian company to use a banned chemical dispersant to help clean up any oil spill in the Bight.
"An oil spill in the Great Australian Bight would be apocalyptic for the region's marine life," the report's author Professor Jodie Rummer said.
"It's hard to imagine that anything could be worse for the Bight than an oil spill but Equinor's use of dispersants will make a terrible situation devastating."
Greenpeace said dispersants mixed with oil were often more toxic to marine life than oil alone and would also pose a threat to workers mobilised to respond to a spill.
Equinor has repeatedly expressed confidence in its ability to drill safely in the Bight and to properly manage any incident.
The company said NOPSEMA's requests for more information were also "part of the normal regulatory process".
If approved Equinor plans to begin drilling its Stromlo-1 exploration well in the summer of 2020/21.
In information released by NOPSEMA, drilling is expected to take 60 days using a mobile offshore drilling unit supported by three offshore vessels and helicopters.
The well will not be cored or production tested for hydrocarbons and will be permanently plugged.
Equinor will then evaluate the results before considering whether to proceed with appraisal or further exploration.