The Sensex at the Bombay Stock Exchange, which opened in the green today but fell in the negative territory in late morning deals, was trading 30 points down at 18,398 in afternoon trade, when reports last came in. The 30-share index had gained 85 points in opening trade at 18,513.In a similar fashion, the wide-based Nifty of the National Stock Exchange was trading 18 points down at 5,589.