As a petroleum producing country, Colombia ranked 8th in world production in 1940. Of the South American countries, Colombia is second to Venezuela, whose output is nearly ten times as great, and slightly ahead of Argentina. At least six petroliferous provinces may be recognized in Colombia. They are the Magdalena Valley, the southwestern basin area of Lake Maracaibo, the plains or "llanos" area in the southeastern part of the country, the coastal area of the Caribbean, the Goajira Peninsula and the Pacific coast region. The most important producing areas at present are the middle Magdalena Valley and the southwestern Lake Maracaibo area. Travel in the country is difficult except in the uplands where most of the roads are located. The native language is Spanish, English b ing spoken only sparingly.

Pre-Cretaceous rocks are known to occur in the Cordilleras Oriental and Central and also in the Llanos area, but are of no importance in the production of petroleum. Cretaceous limestones and shales are extensively developed east of the Central Cordillera and are highly petroliferous. Cenozoic deposits are found in the intermontane valleys, in the Llanos area and along the Caribbean coast. In the middle Magdalena Valley, there are important reservoir beds of petroleum.

Large overthrusts are characteristic features of the Magdalena Valley. They are also known to occur in the Llanos area in the valley west of the Cordillera Central and in the southwestern Lake Maracaibo basin area. In the Magdalena Valley and in the southwestern Lake Maracaibo area petroleum occurs on faulted anticlines. In the coastal region sharp anticlines, with some faulting, are known. Oil and gas seepages and mud volcanoes are of common occurrence. Little is known of the structure of the Goajira Peninsula and the Pacific Coast areas.

Production comes from Oligocene and Eocene sands in the middle Magdalena Valley. Two structures, Infantas and La Cira, produced all the oil of this region up to about 1943. Two new fields have been added to the above producers. The Barco area, located in the southwestern Lake Maracaibo basin, obtains its oil from the Cretaceous and Tertiary on faulted anticlines. In the Cesar Valley, located in the lower Magdalena Valley area, production of high gravity oil from Oligocene limestone has been reported in new wells.

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