Extending yesterday's gains, the Sensex at the Bombay Stock Exchange opened 76 points, or 0.4 per cent higher, at 18,579, this morning, on continued buying by investors. Later, remaining firm, the Sensex stood 68 points, or 0.4 percent in positive territory, at 18,571 in afternoon trade, a short while ago.Stock markets in Japan, China, Singapore, South Korea and Hong Kong were trading mixed, today. Over in the US, the Dow Jones Industrial Average had jumped 1 per cent, overnight.