Recovering from initial losses, the Sensex at the Bombay Stock Exchange closed with a gain of 131 points, or 0.7 percent, at 18,836, today, on fag-end buying by investors, amid the monthly expiry in the derivatives segment. The Nifty at the National Stock Exchange rose 41 points, or 0.7 percent, to 5,683.But stock markets in Japan, China, Hong Kong, Singapore and South Korea lost between 0.2 percent and 2.8 percent.