AN investigation is underway as to the cause of oil spill at an platform in 70 kilometres off the Gippsland coast.
Last week, a sheen on the water was observed close to the Cobia oil production platform, owned by Exxon Mobil and BHP Billiton.
Esso staff responded immediately in accordance with its oil spill response plan.
Following an initial investigation, the Cobia platform was shut down and it will remain shut down while the matter is investigated by Exxon Mobil the National Offshore Petroleum Safety and Environmental Management Authority.
An aerial inspection of the area Monday morning indicated the sheen had dispersed naturally. It was estimated only 750 litres had leaked.