The oil spill was one of the largest in Australian history and according to a Commonwealth government commission of inquiry in 2010, was caused by "systemic" errors of a "more deep seated kind".
When Thailand's PTTEP noted the spill, it evacuated nearly 70 staff from the facility and implemented a spill action plan. The Australian Maritime Safety Authority sprayed more than 180,000 litres of dispersant into the water.
Geoscience Australia estimates the blowout sent up to 2,000 barrels of oil per day into the sea, equating to a total volume of 148,000bbl.
During operations to drill a relief well and plug the leaking well, a fire broke out on the cantilevered portion of the West Atlas jack-up drilling rig, directly above the well head platform.
The fire resulted in the rig collapsing.
Currently PTTEP is fighting a class action law suit in the Australian Federal Court brought by a group of 15,500 Indonesian seaweed farmers claiming damages for the destruction of their crops caused by the spill.
For its part, PTTEP says modelling shows no oil reached the Australian or Indonesian mainland and that 98% of oil remained within Australian waters, most of which was within 23km of the wellhead.
The class action is seeking more than A$200 million worth of compensation from PTTEP.
Lead plaintiff for the action is Daniel Sanda. Sanda's case claims that the seaweed industry in Rote Ndao and Kupang, Indonesia was destroyed by the oil company's failure to safely operate the Montara Wellhead.
Recently PTTEP was served OHS directions and even at one point ordered to shutdown operations on the field by the National Offshore Petroleum Safety and Environmental Management Authority.
Shortly after PTTEP sold the Montara field to junior Jadestone Energy, a deal that closed earlier this month.
Activist groups Greenpeace and the Wilderness Society have launched a campaign connecting PTTEP's oil spill to other proposals to drill in Australian deep waters, including the Great Australian Bight, where Norway's Equinor plans an exploration well late next year or early 2021.
"One of the worst things about this disaster is the failure of governments and the regulator to remedy the flawed inspection process that allowed the spill to occur," Greenpeace Australia Pacific Senior Campaigner Nathaniel Pelle said.
"The anniversary of this institutional failure should serve as a wake-up call as the industry regulator weighs up Equinor's proposal to drill in the rough and ultradeep waters of the Great Australian Bight."
"Equinor is displaying the kind of reckless overconfidence that often precedes catastrophic accidents," Pelle said.
