Thai-owned PTTEP Australasia has accepted full responsibility for the August 2009 oil spill that led to thousands of barrels of oil gushing for weeks on territorial seas between Western Australia and Indonesia.

The company's West Atlas rig in the Montara oil field, located in Timor Sea, ruptured three years ago and the resulting oil leaks covered an estimated 90,000 square kilometres of sea waters, according to figures provided by environmental groups.

The incident is regarded as Australia's worst ever oil spill disaster.

On Thursday, PTTEP Chief Executive Ken Fitzpatrick told the Darwin Magistrate Court that his firm owned up responsibility for the unfortunate accident, which he admitted partly happened due to PTTEP's failure to prevent the spill.

Mr Fitzpatrick also acknowledged that oversights on the part of the oil producer have unnecessarily placed the oil field workers in grave danger.

PTTEP violated the Offshore Petroleum Act and is committed to face the consequent responsibilities, the oil executive told the Aussie court division.

"We've taken full responsibility for the incident, the individuals acted in good faith at the time but the fact remains verified barriers were not in place," Mr Fitzpatrick was reported by Agence France Presse (AFP) as saying.

He vowed too that mistakes on the part of PTTEP will not recur, telling reporters outside the court building that "the Montara incident ... allows us to focus on delivering safe, clean operations in Australia now and in the future."

Clean-up efforts that followed the accident and so-called environmental impacts that ensued have already cost the oil producer some $50 million, Mr Fitzpatrick said, underscoring PTTEP's efforts "within the first few days of the incident to pay for all response costs.

Most importantly, the incident effectively transformed the company's conduct of operations and its culture, he added.

It is likely that the oil producer will face fines of up to $2 million in Australia as determined earlier by a federal inquiry basing on the three charges under the Offshore Petroleum Act, plus breaches under the Greenhouse Gas Storage Act and safe workplace laws.

For its part, the Indonesian government seeks more than $2 billion in compensation, which Jakarta said would cover for damages caused by the oil spill on its fisheries reefs.

But the damages claims attributed directly on the Montara oil spill is being challenged by PTTEP, with Mr Fitzpatrick insisting that "to date we've seen no verifiable scientific data of any damage in Indonesia."

"All of our scientific data indicates no oil reached the Indonesian or the Australian coastline . . . We have seen no indication of any oil reaching Indonesian or Australian coastline and there's been no long-term impact on any species or habitat," the PTTEP chief was quoted by ABC as saying.

He noted that that the data relied on by PTTEP were collected under the direct supervision of the federal Department of Environment.

Greens Senator Rachel Siewert welcomed the news that PTTEP admitted it erred on the incident, but she stressed the company should be made to face the maximum penalties warranted by Australian laws.