The BSE benchmark Sensex, which fell by over 33 points in opening trade today, stood at 11 points in the negative territory at 15,960 when reports last came in. After closing 232 points higher in the previous session, the 30-share Sensex fell by 33 points in the first few minutes of trade today, as investors booked profits recorded in Monday's rally.In a similar fashion, the wide-based National Stock Exchange Nifty Index was trading points 4 in the red at 4,774.Brokers said profit-booking of Monday's gains by speculators was mainly responsible for the moderate fall in stock prices, but buying in select scrips following news that the output of key infrastructure sectors grew by 6.8 per cent in November limited the losses.