The Sensex at the Bombay Stock Exchange gained 75 points, or 0.5 per cent, to 15,619 in the first five minutes of trade, this morning, on fresh buying by investors, amid firm Asian bourses.Later, the Sensex gained some more ground, to stand 105 points, or 0.7 percent in positive territory, at 15,649 in afternoon trade.The 30-share Sensex had lost more than 400 points in the past three trading sessions.Other Asian markets in Japan, China, Hong Kong and Indonesia were up by between 0.2 percent and 0.8 percent, today, following encouraging economic data from the US.Across on Wall Street, the Dow Jones Industrial Average had gained 1.1 per cent, overnight.