Rising for the third straight session, the Sensex at the Bombay Stock Exchange gained 158 points, or 0.8 percent, to close at 19,962, today, ahead of the US Federal Reserve's decision on monthly bond purchases. The Nifty at the National Stock Exchange rose 49 points, or 0.8 percent, to 5,899.Stock markets in Japan, China, and Singapore rose between 0.3 percent and 1.4 percent.