Sydney, Aug 22 (DPA) Oil spilled from a drilling rig 690 km west of the Australian city of Darwin Saturday as a cleanup operation was beginning to get underway.

The Australian Maritime Oil Spill Centre said Hercules aircraft were expected to begin spraying 50,000 litres of dispersant.

All 69 workers were taken off the West Atlas drilling platform when the leak was discovered Friday.

The centre said there was an 8-km oil slick in the Timor Sea but that the petrochemicals were evaporating. 'That indicates that the oil is breaking down naturally and any application of dispersant would only enhance the breakdown of the slick,' centre spokesman Ivan Skibinski said.

The operator of the rig, Bangkok-based PTTEP Australasia, said in a statement that it was unlikely the spill would reach the coast.

'PTTEP is continually planning to determine how the leak can be brought under control so the West Atlas can be safely reboarded and begun to be restored to working order,' a statement said.