The Sensex at the Bombay Stock Exchange gained 84 points, or 0.5 per cent, to 18,350 in opening trade, today, on the back of fresh buying by investors, amid a firm trend on the other key Asian bourses. Later, the Sensex gained more than 100 points. But it then trimmed its gains, to stand a smaller 27 points, or 0.2 percent in positive territory, at 18,293 in afternoon deals, a short while ago. The 30-share BSE index has lost over 220 points in the past four sessions.Other stock markets in Japan, China, Hong Kong, Singapore, Indonesia, Taiwan, and South Korea were up by between 0.1 percent and 1.3 percent, today, after data from China showed some positive signals on the Chinese economy.