A company responsible for a massive oil leak in the Timor Sea says it could take up to seven years to deal with the environmental impact of the spill.

PTTEP Australasia plugged the leak and extinguished a fire at its West Atlas oil rig yesterday.

For 74 days oil and gas flowed uncontrollably from the PTTEP Australasia's Montara wellhead into the waters of the Timor Sea.

Up to 400 barrels of oil a day had been leaking from the well, which took engineers four attempts to plug.

The Federal Government has announced a formal inquiry into the spill.

Company spokesman Jose Martins has told the ABC the clean-up should be carried out quickly.

"I suspect a couple of months is what we are sort of anticipating," he said.

"The environmental plan really could take up to seven years.

Asked whether the company should apologise, he said: "We regret what's happened and I think the rest will have to come out in the inquiry."

Mr Martins says the company already knows what caused the blaze but will not say.

"There's a range of causes but we're not going to go into that," he said.

Piers Verstegen from the Conservation Council says the incident is an environmental catastrophe.

"Once you release that much oil and pollution and toxicity into the environment, the threat to the environment continues for a long time," he said.

"We need that to be monitored to ensure that the company actually pays for the impact of that damage, but most importantly we need to ensure that this doesn't happen again."