The San Pedro oil field, in the Province of Salta, is the most important of the seven fields of northern Argentina and has produced about half of the total of 24,800,000 barrels obtained to the end of 1944 from that region. These fields account for about 10 per cent of the crude oil production of the entire Republic. San Pedro itself produced 12,941,259 barrels of oil, or 27,771 barrels per acre recovery to the end of 1944. This is a relatively high recovery for Paleozoic oil.

The San Pedro field, like the others of the region, is situated in the Tarija Basin of Permo-Carboniferous age, with total sedimentary deposits probably exceeding 10,000 meters in thickness. The oil within the fields of this basin is considered to be primarily of Devonian origin and is found irregularly accumulated in various formations up to and including Pleistocene. In this field, the oil zones are just above the Devonian in the glacial sediments of the Permo-Carboniferous.

The structures of the Tarija Basin were formed during the Andean movement of Pleistocene age, there being no noticeable differential folding in the thick section from Devonian to Pleistocene. They are in a belt of about 100 kilometers wide between the "altiplano" and the "Chaco" plain on the east, and stand out as five or more long, parallel mountain ranges several hundred kilometers long. The characteristic form of the structures is a thrust-faulted anticline, and in a number of places it appears that the faulting has been the dominant feature, folding being somewhat superficial and late in the structural development.

The oil fields within the Tarija Basin are unique among those of the world in their relatively great age disparity between the deposition of the source beds (Devonian) and the first folding (late Tertiary) which could have afforded accumulation. From this it is inferred that possibly the generation and migration of oil from a source bed could be postponed, without adverse results, until the advent of the first effective folding.