Fos-sur-Mer is a commune in the Bouches-du-Rhone department in southern France.
Fos-sur-Mer is situated about 50 km (31 mi) north west of Marseille, along the mediterranean coast, and on the west of the Etang de Berre. The city has 6 km (3.7 mi) of sand beach.
The city attracts many industries. Among others the steel industry. The steel giant ArcelorMittal has a steel plant called Sollac Mediterranee overhere. Because of the steel, chemistry and oil industry the city is amongst the most polluted towns in Europe.