The Sensex at the Bombay Stock Exchange surged 247 points to 18,737, in opening trade, this morning, on continued buying by funds, amid firm global bourses. But the benchmark index later surrendered most of its initial gains, to stand a much more modest 63 points in the positive zone, at 18,553, in afternoon deals, a short while ago. The Sensex has already rallied more than 865 points in the past four trading sessions.Other regional markets in Japan, China, Hong Kong, Singapore, South Korea and Taiwan were up by between 0.5 percent and 1.7 percent, today.