Building on its initial gains, the Sensex at the Bombay Stock Exchange had advanced 138 points, or 0.7 percent, to 20,367 in somewhat volatile afternoon trade, a short while ago. Earlier in the morning, the Sensex had climbed 109 points, or 0.5 per cent, to 20,339, on fresh buying by funds and retail investors. The 30-share Sensex had lost over 660 points in the previous two trading sessions. Stock markets in Japan, China, Taiwan, Hong Kong, South Korea, Indonesia and Singapore were trading mixed, today. But the US Dow Jones Industrial Average had gained 0.7 percent, to close above the 16,000-mark for the first time, yesterday.