Rising for the third straight session, the Sensex at the Bombay Stock Exchange ended with a marginal gain of 24 points, or 0.1 percent, at 20,273, after volatile trade, today. The Sensex had climbed over 350 points in the previous two trading sessions. The Nifty at the National Stock Exchange rose 14 points, or 0.2 percent, to 6,021.Stock markets in Japan, China, Hong Kong, South Korea and Singapore ended mixed.