Colombia is located in the extreme northwestern part of South America and falls within the tropical zone. One half of the country consists of mountains and valleys while the other half is plains or "llanos." Travel within the country is usually difficult except between the larger cities which are connected by airplane. Three prominent ranges of mountains with their intermontane valleys comprise the mountain province. The Magdalena Valley between the eastern and central ranges is at present the most important petroleum-producing section. Two geosynclinal areas of deposition are recognized. The North Andean geosyncline located in the eastern part of the country and whose axis trends N. 25°-30° E. was the locus of deposition of Cretaceous and early Tertiary sedimen s. At the close of the Cretaceous, downwarping produced the Tertiary Bolivar geosyncline between the present western and coastal ranges. This geosyncline was terminated in the late Tertiary Andean revolution. Tertiary deposits are also widespread along the north coast of the country as well as in the Magdalena Valley. Overthrust structures are common in the eastern portion of the country. Petroleum occurs on asymmetric anticlines which are in places complexly faulted.

Six potential petroliferous provinces may be recognized. Of these, the Magdalena Valley and the Barco Concession located in the Southwest Lake Maracaibo drainage area are at present the most important producing regions. Considerable activity is being carried on both in the Llanos and in the North Coast areas.

Colombia normally ranks about eighth in world production with approximately 25,000,000 barrels a year output. In South America, it is second to Venezuela, whose production is nearly ten times as great, and slightly ahead of Argentina and Trinidad. The country is now being systematically studied by both geological and geophysical means.