Fos-sur-Mer (French pronunciation: [fɔs syʁ mɛʁ], literally Fos on Sea; Provençal: Fòs) is a commune in the Bouches-du-Rhône department in southern France.

Fos-sur-Mer is situated about 50 km (31 mi) north west of Marseille, on the Mediterranean coast, and to the west of the Étang de Berre.

The city has 6 km (3.7 mi) of sand beach.

The presence of the steel, chemistry and oil industries means that pollution levels are high.

Fos-sur-Mer is home to Fos Provence Basket which plays its home games at the 2,000 seat Complexe sportif Parsemain.