The Sensex at the Bombay Stock Exchange gained 138 points, or 0.8 per cent, to 17,985 in opening trade, on Thursday morning, on fresh buying in select stocks, amid positive Asian bourses. Rising further, the Sensex later regained the 18,000 level, only to slip back once again, and stand 137 points, or 0.8 percent in positive territory, at 17,984, in afternoon deals, a short while ago. Stock markets in Japan, China, Singapore, Hong Kong, South Korea and Taiwan were up by between 0.2 percent and 2.8 percent, today. The US Dow Jones Industrial Average had ended 0.3 per cent higher, overnight.