Amerisur Resources, an oil and gas producer and explorer focused on South America, rose following a positive drilling update.Its Platinillo-5 well in Colombia, the third well of a planned eight well drilling campaign, has found oil in the U sands of the Villeta formation. Two further zones within the Villeta may also contain potential pay and are under evaluation.John Wardle, Chief Executive, commented: "I'm very pleased with the well results to date and look forward to updating the shareholders on flow data very shortly."House broker RBC Capital Markets has Amerisur as a top pick, albeit in the speculative risk category.CM