Sensex has gone up by 31 points in noon trade at 19635 points a short while ago. The 30-share barometer, which gained over 511 points in the previous session, fell by 70.89 points to 19,531 in the first few minutes of trade today, led by a fall in oil and gas, metal and power sector stocks. Similarly, the wide-based National Stock Exchange index Nifty gained 5 point to 5888 points.