The Sensex continues to maintain its opening gains in the afternoon trade. The Sensex was trading up by 253 points at 16486 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 68 points at 4956 a short while ago. The NSE gained 16 points in early trade today.