PTTEP Australasia says the operation to plug and secure the Montara well head platform has been completed, some four months after oil started leaking into the Timor Sea.
The company's chief financial officer Jose Martins said PTTEP is continuing to monitor the platform, which started spewing oil, gas and condensate into the ocean, 250 kilometres from shore, in late August.
"The situation at Montara continues to be challenging," Mr Matins said.
"There are many steps to be undertaken before we can make full assessments of the status of the platform and development work can be resumed in 2010 to safely bring the Montara field into production."
The spill is estimated to have cost the Thailand company at least $170 million.
PTTEP first plugged the well in early November using 3,400 barrels of heavy mud after several earlier misses. The company then poured cement into the well to secure the leak.
Operations were interrupted in December when Cyclone Laurence hit the area, which did not impact the offshore facilities.
Last year, Resources and Energy Minister Martin Ferguson announced there will be an inquiry into the oil spill.
