More than 15,000 Indonesian seaweed farmers stand to be compensated over one of Australia’s largest oil spills after they won a protracted class action battle against the company that ran the rig off the coast of Western Australia.

The Federal Court found the 2009 Montara oil spill travelled 240 kilometres into Indonesian waters and destroyed the seaweed crops and livelihood of West Timor farmers.

The court found on Friday that the company that operated the rig, PTTEP Australasia, had breached its duty of care to the farmers by failing to properly seal the well, which created a “very high risk of blowout”.

Justice David Yates said there was no other plausible explanation for the widespread loss to the farmers of the Kupang and Rote Ndao regions other than the oil spill.