The Sensex at the Bombay Stock Exchange gained 18 points, or 0.10 percent, at 18,650, a short while ago. Earlier in the morning, the Sensex had opened 77 points up, on the back of covering-up of short positions by participants in view of monthly expiry in the derivatives segment.The 30-share index, which had shed 62.24 points yesterday, moved up by 77.13 points, or 0.41 per cent, to18,709.30.Similarly, the wide-based National Stock Exchange index Nifty was up 2 points, or 0.33 per cent, to 5,665.Stock markets in Asia, Hong Kong's Hang Seng gained 0.44 per cent, while Japan's Nikkei Index fell by 0.21 per cent. The US dow Jones Industrial Average ended 0.33 per cent down in yesterday's trade.