PTTEP estimates the well is leaking 400 barrels of oil a day, but the Australian government said the maximum flow could be as much as 2,000 barrels a day.

"The simple fact is we don't know how much oil has been released into the environment," Rachel Siewert, a Greens senator, said.

"I've always been sceptical about the company's claim of 300-400 barrels, because they could never back it up."

Marine life threatened

Satellite images show a surface slick estimated at 15,000sq km, stretching into Indonesian waters.

"We were in an area that is teeming with marine life ... It was sickening, because we were seeing dolphins surfacing in the oil and birds feeding in it," Gilly Llewellyn of the World Wildlife Fund said following a survey of the slick.

"If this was closer to shore there would be global outrage. We are not seeing large amounts of birds dying but this will have a serious long-term impact," she said. 


 Interview with Gilly Lewellyn, WWF director

PTTEP is using electromagnetic ranging tools to home in on the damaged casing, and is calculating each failed drill attempt's distance from the pipe.

About 300 people are working on addressing the spill PTTEP said.

Seventeen vessels and nine aircraft, including a Boeing 747, have been used in the operation.

The cost of the clean-up has reach A$5.3 million (US$4.9 million), a senate hearing heard this week.

PTTEP has said it will pick up the bill for the operation.

The leak, which began on August 21, is more than two and a half kilometres below the sea bed.