Sensex at the Bombay Stock Exchange gained 131 points to 20,830 in late morning deals today on emergence of buying by funds in oil and gas, IT, banking and consumer durables sector stocks amid a mixed Asian trend. The 30-share barometer rose by 117 points in opening trade today.Key benchmark indices in Hong Kong, China, Japan and Indonesia fell between 0.5 per cent and 0.96 per cent, while those in Taiwan, Singapore and South Korea rose between 0.18 per cent and 0.26 per cent.Nifty at the National Stock Exchange also gained 37 points to 6197.