To date, 20 horizontal wells have been drilled in Colombia: 16 in sandstone, and four in carbonate reservoirs. In carbonate, the economical success rate is 50%, but in sandstone it is 88%. In general, wells in Colombia are expensive. The vertical well cost varied from $2 million to $11 million, depending upon the reservoir depth. Horizontal well costs vary from 1.5 to 2.5 times the vertical well costs. Initially, most of the wells were completed ,with slotted liners. Now, new wells are completed with cemented and perforated liners to control water and gas production. The range of True Vertical Depth (TVD) is between 914 in (3,000 ft.) and 4,880 m (16,000 ft.). This paper presents three brief field histories, and the lessons learned to date. In cases where production is less than expected, principal causes are: (i) A horizontal well has commingled production from zones of high contrast in permeability, reducing considerably the producing length of a horizontal well. (ii) Production of unwanted fluid such as water and gas. With slotted liner completion, it is not only difficult to identify gas and water producing zones, but it is also difficult to isolate them effectively. (iii) Geological uncertainty, which results in drilling a well through a zone which is geologically different than expected. New horizontal wells are planned as short length wells in high permeability zones, and long ones in low permeability zones. Also, re-entry wells are now used in mature reservoirs to reduce drilling costs. The method used to analyse the well performance is discussed length, gamma.-cussed in the paper. To determine the pi ray analysis, log information, production tests and/or production logs were used. A productivity analysis using analytical equations was also conducted to define if the well was damaged or gad a small producing length. Then, decline curve analysis was sed to forecast rate and reserves, and well production histories were matched for rates and cumulative production over time. Depending upon the problem, and considering feasibility and cost effectiveness, a corrective action was designed to improve well productivity. In summary, horizontal wells in Colombia have been successful and a large potential exists to drill many more wells.