We present a tectonic analysis of the Camargue and Western Proven¿al margin based on geophysical maps, seismic profiles, and well log data. The tectonic style results from a polyphase geological history. Mesozoic extension was followed by Late Cretaceous-Eocene compression. During Oligocene extension, part of the preexisting compressional structures was reactivated along extensional detachments. The concept of Oligocene negative inversion is applied to an asymmetrical opening of the northwestern Mediterranean basin. The steep Proven¿al margin is separated from the extended Gulf of Lion margin by a major transfer zone. The extensional structures of the Gulf of Lion can be placed in the framework of the Western European rift system. Late Eocene-early Oligocene E-W extension is followed by NE-SW late Oligocene-early Aquitanian opening of previous transverse structures. Seismic evidence supports a possible eastward extension of the North Pyrenean fault. ¿ American Geophysical Union 1996