The Sensex at the Bombay Stock Exchange gained 14 points, or 0.1 percent, to close at 20,005 on Wednesday, ahead of the monthly expiry in the derivatives segment.The Nifty at the National Stock Exchange rose 6 points, or 0.1 percent, to 6,056.Stock markets in Japan, China, Hong Kong, South Korea and Singapore climbed between 0.4 percent and 2.3 percent.