The Bombay Stock Exchange benchmark Sensex is trading with marginal gains after opening nearly 129 points higher in the morning. Failing to maintain the initial gains market was up by around 49 points at 17928. Buying was seen in select pharma, FMCG and oil and gas stocks while realty and IT stocks are down. The 30-share barometer, which lost nearly over 480 points in the previous two sessions, rose by 128 points, or 0.72 per cent, to 18,007 in the first few minutes of trade on Monday. Similarly NIFTY crossed the psychological 5400 mark immediately after opening in the morning but could not stay there for long and was trading at 5390, which is up by 16 points.