The Montara oil field sits in the Timor Sea approximately 690 kilometres southwest of Darwin, in Australian waters operated by PTTEP Australasia — a subsidiary of a Thai state petroleum company. The wellhead platform was in approximately 250 feet of water, the hole itself drilled 1.6 miles below the seabed. When the well blew out on 21 August 2009, initial estimates placed the leak at 400 barrels per day. The Australian Department of Resources, Energy and Tourism later estimated it could be as high as 2,000 barrels per day — five times that figure. Four separate attempts to plug the well failed. On 1 November, as engineers attempted yet again to close it, a fire broke out on the West Atlas drilling rig. The fire burned through the night, the flames consuming the leaking oil and thereby temporarily reducing the surface slick. On 3 November, the fifth attempt worked: PTTEP pumped approximately 3,400 barrels of drilling mud into a relief well, stopping the flow. A 1,400-metre cement plug followed. The well was finally capped in January 2010.

Within two weeks of the initial blowout, the Australian Maritime Safety Authority reported that the slick had spread over 6,000 square kilometres of ocean and was moving closer to the Western Australian coast, sitting 170 kilometres from shore. The oil was killing marine life across a vast area. Daily overflights through September and October identified isolated patches of weathered oil reaching as far as Indonesian waters — patches spotted 94 kilometres southeast of Roti Island, with the main slick about 248 kilometres from the Indonesian coastline. Indonesian fishermen, who worked those waters regularly, reported significant damage to their livelihoods. A subsequent environmental study, conducted in October 2009 and released in July 2010, found no traces of hydrocarbons in water or shoreline sediments between Camden Sound and the Stewart Islands on the Kimberley coast — a finding that drew relief but also considerable scepticism from environmental groups.

The Montara spill exposed gaps in Australian offshore safety regulation that a subsequent government inquiry documented in detail. The West Australian government, environmental groups including WWF-Australia, and Australian Greens senators argued loudly that the true scale of the spill had been understated throughout the emergency. The Indonesian fishermen who lost income during the 74-day leak — and in the months it took for the affected waters to recover — sought compensation and investigation. Their claims, which reached Australian courts, became one of the most significant transnational legal proceedings arising from an Australian offshore environmental incident. The West Atlas drilling rig itself was eventually removed from the Montara wellhead platform in a separate operation beginning in August 2010 and towed to Singapore for decommissioning.

The Timor Sea is not a high-traffic area. The spill did not wash up on tourist beaches or close major ports. Its victims were fish, seabirds, marine mammals, and the Indonesian fishermen whose income depended on the health of waters they had worked for generations. These are the kinds of victims who are easiest to overlook when calculating the cost of offshore accidents — easy to underestimate, hard to compensate, and far from the decision-makers who set the safety standards that failed. The Montara blowout did result in tightened offshore well integrity requirements for Australian operations. Whether those changes are sufficient to prevent a recurrence is the kind of question that offshore regulators, fishing communities, and marine ecologists continue to answer very differently.