The A27 in Lancing has been closed after a collision left oil all over the road.
The eastbound carriageway has been closed from the junction with Busticle Lane and the Manor Roundabout.
Sussex Police said the collision between a lorry and car at 11.17am had left 'a lot of oil' on the highway.
Traffic is queuing along the eastbound carriageway as far as the Grove Lodge roundabout.
An eyewitness reported a Royal Mail truck colliding with a car as it travelled north from Busticle Lane.