Environmental groups have criticised the government's handling of the spill, saying it is threatening bird and marine life off Western Australia's resource-rich north coast.
"We are ranking it as a major environmental disaster," John Carey, a spokesman for the global Pew Environment Group, told AFP, adding that oil was a slow and silent killer for many marine species.
The area was a "marine superhighway for species moving in and out of the region so it's an area of global importance," he said.
"In terms of the greater northwest region, you are looking at up to almost one quarter of dolphins and whales in the world in this area."