Petrobras finds oil in Colombia's Upper Magdalena Valley Basin

* Discovery is of medium-grade crude oil * Well producing 500 barrels/day in test * Find in Boquerón Block in Tolima province RIO DE JANEIRO, Dec 19 (Reuters) - Brazil's state-led oilcompany Petroleo Brasileiro SA said on Wednesday thatit found medium grade crude oil in a well drilled in the UpperMagdalena Valley Basin in Colombia's Tolima province, apotential expansion of an existing production area. The oil, at 23.9 degrees on the American Petroleum Institute(API) scale, was found in the Guando SW1 well drilled to a finaldepth of 1,576 meters (5,171 feet), the Rio de Janeiro-based oilcompany said in a statement. Medium grade crude is heavier and worth less than high-grade"light" oil but worth more than thicker heavy grades of crude.Medium crude is rated 22.3 to 31.1 degrees on the API scale. Thehigher the number the "lighter" the oil. The Petrobras discovery is part of work to restartexploration in the Boquerón Block, which is in production.Petrobras has been working in the area for 12 years. Boquerón ishome to the Guando Field, one of the biggest discoveries inColombia in the last 15 years, Petrobras said. Guando, about 110 kilometers southeast of Bogotá, has anestimated 126 million barrels of recoverable oil, or enough tosupply all of Colombia's oil needs for about a year and a half,according to Reuters and BP Plc. Petrobras has 15 exploration projects in Colombia, sixoffshore and the rest, including the latest discovery, on land,the company said. On Oct. 27, Petrobras began a long-duration test on theGuando SW1 well which is showing initial production levels ofabout 500 barrels of oil a day. Further tests are needed to determine the potential of thediscovery, Petrobras said. Petrobras preferred shares, the company's most-traded classof stock, rose 3.77 percent to 20.93 reais on Sao Paulo'sBM&FBovespa exchange, the company's biggest one-day jump inthree months and highest close in six weeks. Petrobras announced the discovery after the market closed.