Falling for the fourth straight session, the Sensex at the Bombay Stock Exchange ended with a marginal loss of 12 points, or 0.1 percent, at 18,197, amid weak global markets, on Friday. The Nifty at the National Stock Exchange fell 6 points, or 0.1 percent, to 5,482.Stock markets in Japan, China, Hong Kong and South Korea lost between 0.3 percent and 1 percent.