Maintaining the upward trend, the Bombay Stock Exchange benchmark Sensex was trading up by 168 points, at 18,015 a short while ago. Sensex rose by over 137 points in opening trade today on fresh buying by funds and retail investors in select stocks amid a firming trend on other Asian bourses. The 30-share barometer had lost 164.73 points in yesterday's trade. The wide-based National Stock Exchange Nifty index was also trading in green at 5,397 points, up by 48 points.