Rising for the third straight session, the Sensex at the Bombay Stock Exchange gained a marginal 7 points, to close at 19,643, amid positive Asian markets, on wednesday. The Sensex had gained over 167 points in the previous two trading sessions. The Nifty at the National Stock Exchange rose 3 points, or 0.1 percent, to 5,943.Stock markets in Japan, China, Hong Kong, South Korea and Singapore climbed between 0.4 percent and 2 percent.