One of the seas that comprise the western basin of the Mediterranean Sea which is sometimes called the Catalan Sea. It lies between the Iberian coast and the Balearic Islands (Ibiza, Mallorca, Menorca) in the northwestern Mediterranean. It is separated from the Tyrrhenian Sea to the east by Sardinia and Corsica and abuts the Alboran Sea to the west. The bathymetry is dominated by the Balearic Abyssal Plain, which covers over 30,000 square miles, covering the majority of the basin floor at depths ranging from 2700-2800 m. This is bordered to the northwest by the Rhone Fan, a large sedimentary cone.

The circulation can be seen to first order to be a single oblong cyclonic cell with a divergence zone aligned with the shape of the basin. More detailed studies have shown the surface circulation to be strong year-round and characterizied by two permanent density fronts. These are the Catalan Front on the continental shelf slope and the Balearic Front on the Balearic Islands shelf slope, with the former the more active. The northern area a plume of cold water frequently seen moving southward along the continental slope and shedding dipole eddies along its leading edge. Energetic filaments continuously spawned by the Catalan Front seem to be associated with this plume.