The Sensex at the Bombay Stock Exchange gained 49 points, or 0.3 percent, to 18,759, on Thursday, supported by some quarterly corporate earnings and firm Asian and European markets, amid the monthly settlement of the derivatives contracts.The Nifty at the National Stock Exchange rose 14 points, to 5,705.Stock markets in Japan, Hong Kong, South Korea and Singapore rose between 0.2 percent and 1 percent.