The BSE benchmark Sensex was trading up by 256 points at 16488 a short while ago. The Sensex opened 77 points higher in early trade today, extending Friday's gains on continued buying by foreign funds amid a firming trend overseas. The wide-based National Stock Exchange index Nifty was also trading up by 71 points at 4959.20 a short while ago. The NSE gained 16 points in early trade on Monday.