The Aquitaine Basin in southwestern France, just north of the Pyrenees, is a large Mesozoic and Tertiary basin about 200 miles across. The French Government and private interests are presently exploiting parts of it for oil and gas in two concessions. One area of structures near the Pyrenees has already been proved to have commercial quantities of gas and is being actively developed.

The strata of greatest importance as containers of oil are the Jurassic and Upper Cretaceous. Of these two the Jurassic seems most promising. The possible oil-bearing strata are not thick presumably, and the Jurassic may be reached between 1,500 and 3,000 feet in the central part of the basin.

A zone of rather intense folding with gypsiferous shale in plugs or demies (Keuper shale of Upper Triassic) renders a piedmont or foothill belt to the Pyrenees not improbable for oil and gas discovery but so complex structurally as to be rather precarious for preliminary development. The area immediately north of the zone of plugs seems to be one of gentle folds and the most promising for immediate prospecting. It is extensively blanketed with alluvium and the structures will have to be defined mostly by geophysical prospecting or by shallow test drilling. The latter is well adapted to the region because of the abundance of microfossils in both the Tertiary and Cretaceous strata for subsurface correlation.