The Aquitaine Basin, situated in southwest France, with an area of about 60 000 km2, has the form of a triangle which opens towards the Atlantic (Bay of Biscay) and is limited to the north by the Hercynian basement of Brittany and the Massif Central, and to the south by the Pyrenean Tertiary orogenic belt. Beneath the Tertiary sequence (2 km thick, and which outcrops over much of the basin) a Mesozoic series, up to 10 km thick, rests generally on a tectonized Hercynian basement but locally it covers narrow (NW-SE-trending) post-orogenic trenches of Stephano-Permian age. The Mesozoic history can be subdivided into four major structural-sedimentary episodes: (1) during a Triassic taphrogenic phase a continental-evaporitic complex developed with associated basic magmatism; (2) throughout the Jurassic, a vast lagoonal platform developed, initially (Lower Lias) as a thick evaporitic sequence followed by a uniform shale-carbonate unit, indicating a relative structural stability; (3) the end of the Jurassic and the Lower Cretaceous saw a fragmentation of this platform, due to an interplay between the Iberian and European tectonic plates, resulting in an ensemble of strongly subsident sub-basins; (4) during the Upper Cretaceous and until the end of the Neogene, the evolution of the Aquitaine Basin was influenced by the Pyrenean orogenic phase, with the development, towards the south, of a trench infilled by flysch which, from the Upper Eocene, is succeeded by a thick post-orogenic molasse complex. The main hydrocarbon objectives in the basin are situated in the Jurassic platform (e.g. the Lacq giant gas field) and the Cretaceous sub-basins (e.g. the Cazaux and Parentis oil fields). To date, production has been about 4 x 107 m3 of oil, and about 15 x 1010 m3 of gas since the first gas discovery (St Marcet) in 1939.