Falling for the fourth straight session, the Sensex at the Bombay Stock Exchange declined 141 points, or 0.8 percent, to close at 17,491, on selling ahead of the settlement in this month's derivatives contracts, amid weak global markets, today. The Sensex had lost almost 220 points in the last three trading sessions. The Nifty at the National Stock Exchange fell 47 points, or 0.9 percent, to 5,288.Stock markets in Japan, China, Hong Kong, South Korea and Singapore again ended mixed.