Rising for the fourth straight session, the Sensex at the Bombay Stock Exchange ended with a marginal gain of 7 points, at 18,763, after volatile on Monday. The Sensex had gained 324 points in the previous three trading sessions. The Nifty at the National Stock Exchange also rose 7 points, to 5,704.But stock markets in Japan, China, Hong Kong, South Korea and Singapore declined between 0.1 percent and 0.6 percent, amid investor caution ahead of the US Presidential elections.