Surrendering all its initial gains, the Sensex at the Bombay Stock Exchange, stood 135 points, or 0.7 percent in the red, at 20,167, in afternoon deals, a short while ago. Earlier, the Sensex had opened 125 points in the green, at 20,426, on fresh buying by investors.Stock markets in Japan, China, Singapore, Hong Kong and South Korea wre trading mixed, today. In the US, the Dow Jones Industrial Index had gained 0.3 per cent, overnight.