The Sensex at the Bombay Stock Exchange gained 104 points or 0.61 per cent and was trading in positive territory at 17,285, a short while ago.Earlier, the 30-share barometer rose by 129 points in opening trade today, continuing its gaining streak for thethird straight day. The gain was attributed to sustained buying by funds and retailers, tracking a firming trend in Asian region. In a similar fashion, the Nifty at the National Stock Exchange moved up by 31 points to 5,247.