The Sensex at the Bombay stock Exchange gained 87 points, or 0.4 per cent, to 19,504 in early trade, today, due to short-covering by market participants, following the monthly expiry in the derivatives segment. But later, the Sensex gave up all its initial gains, and stood 30 points, or 0.2 percent in negative territory, at 19,388 in afternoon deals, a short while ago.Key stock indices in Japan, Hong Kong, Indonesia, Singapore, Taiwan and South Korea were up by between 0.2 percent and 0.9 percent, today. The US dow Jones Industrial Average, had ended 0.2 per cent lower in yesterday's trade.