The Llanos of Colombia, comprising the eastern portion of the country, is an alluvium-covered, featureless, grassy plain that covers an area of about 75,000 square miles. Except for a short dry season from December to March heavy rains occur almost every day. Access to the area is difficult and for the major portion of the year special track equipment or helicopters must be used for exploration operations. Structurally the Llanos form an asymmetrical basin similar to that of eastern Venezuela or western Canada. There is a shelf area to the east with sediments dipping uniformly off the Guiana shield and increasing in thickness to the west to form a major trough in front of the thrust faulted Eastern Cordillera. The entire geological sedimentary column outcrops along the we tern border of the Llanos with excellent reservoirs, source rocks, and attendant oil seeps. Approximately 26,500,000 acres are held in the basin by six major oil companies at this time. To date the geology of the bordering Eastern Cordillera has been mapped in considerable detail, reconnaissance seismograph, gravity, and local magnetometer surveys have been run over the more attractive portions of the basin, and 22 wells have been drilled. Although some encouraging oil shows have been encountered in wells in the southern margin of the basin, no commercial oil has been discovered to date.

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