The benchmark Sensex at the Bombay Stock Exchange gained 31 points in early trade today on the back of covering-up of short positions by participants following monthly expiry in the derivatives segment. The 30-share index, which had shed 83 points in the previous session on Tuesday, moved up by 31.51 points to 18,741 with oil and gas, metals and realty sector stocks leading the recovery.Similarly, the wide-based National Stock Exchange index Nifty was up by 7 points to 5,697. The markets remained closed yesterday on account of "Dussehra".In Asia, Hong Kong market gained 0.17 per cent, while Japan's Nikkei Index was up by 0.34 per cent. The US dow Jones Industrial Average, however, ended 0.19 per cent lower in yesterday's trade.