Previous to 1917 eight tests for oil or gas were made in this territory. In 1925 the search for oil was taken over by the Chilean Government and up to 1942 the Departamento de Minas y Petroleo made 7 tests which, though not producing commercially, found good showings of oil and gas in two different zones and in three different localities. In 1942 the search for oil was taken over by the Corporacion de Fomento de la Produccion and since that time one oil field has been found, partly developed, and another wildcat well, San Sebastian No. 1, has found 19 meters of oil-saturated sand in the same zone.

The oldest sediments studied for oil production are probably Jurassic. This series is thought to be the equivalent of the Serie Porfirica of Argentina. About 6,600 meters of Upper Cretaceous and 5,000 meters of Tertiary rocks, all of which are marine sediments, have been measured. An unmeasured series, approximately 2,000 meters thick, of non-marine Tertiary deposits lies above the marine sediments. Much of the territory is covered by a blanket of fluvio-glacial deposits of unknown thickness.

The principal sedimentary feature is the Magallanes basin the west side of which is just east of the Cordillera front and the east side of which is unknown, but drilling to date indicates it to be at or east of the Manantiales field as 6,000-8,000 meters of rocks have been cut out in that area.

Four major and an uncounted number of minor unconformities have been recognized in this territory.

In general the rocks nearest the Cordillera are crushed and crumpled, and somewhat farther removed they are steeply folded and still farther eastward the folds are gentler and broader. Strike faults have also been developed.

In view of the great thickness of marine sediments and the fact that one oil field and indications of another already exist on the east flank, the possibilities of finding additional commercial oil appear good.