Indonesian seaweed farmers are fighting for more than $200 million in compensation after a 2009 oil spill in the Timor Sea.

More than 13,000 Indonesian farmers are party to the class action brought by law firm Maurice Blackburn before the Federal Court in Sydney.

The Montara disaster was Australia’s largest ever oil spill, caused by a massive blowout at a well drilled by a subsidiary of the Thai Government’s oil firm PTT Exploration and Production Public Company (PTTEP).

The farmers are suing the subsidiary - PTTEP Australasia (Ashmore Cartier) Pty Ltd – for damages that devastated their livelihoods.

“They are claiming compensation for the loss and suffering caused by the negligence of the oil rig operator,” says principal lawyer Ben Slade.

“We say that runs into hundreds of millions of dollars. Our assessment to date is something north of $200 million that they are entitled to.

“Our investigations show that the operator of the oil rig has a serious case to answer for cutting corners that endangered lives, the environment and the livelihoods of thousands of seaweed farmers.”

The spill happened in Australian waters about 700 kilometres west of Darwin, dumping an estimated 300,000 litres of oil into the Timor Sea each day for 10 weeks.

Four years after the spill, in 2013, PTTEP Australasia announced the Montara Environmental Monitoring Program had given that part of the Timer Sea “a clean bill of health”.

The program was developed by PTTEP in collaboration with the Australian Government.

Mr Slade said PTTEP Australasia had failed in its duty of care to the farmers.

“Things were going really well for their community and, in fact, they had a bumper year in 2008 but towards the end of 2009 everything stopped and their crops died,” he said.

“It was really quite a horrific incident and the company has for many years now tried to avoid compensating the Indonesians who suffered so greatly.

“They have taken many years to get back to any sense of normal production.

Mr Slade said just getting the evidence together was a major challenge.

“This case is replete with many problems. The analysis of the losses is difficult, but there are records, people paid tax.

“The records are there, it's just a big job to get it together.”