Reports of an oil spill in the southbound lanes of the Princes Motorway came just before 3pm. 

The first southbound lane, around 300metres from the Mount Plesasant overpass, was closed for an hour.

Passing motorists advised fire crews the spill actually started much higher up the mountain, around the area of Clive Bissel Drive, near the truckstop at the peak of the hill.

Clive Bissel Drive is a road that runs parallel to Appin Road between the Princes Motorway and Mount Kembla Road.

Police and fire crews poured sand on one smaller spill at the top of the mountain, and a larger one midway down the hill.

Southbound traffic was heavy through the afternoon, but the road was reopened as normal by 4pm.