The Bombay Stock Exchange benchmark Sensex declined by over 40 points at mid session on Tuesday as investors sold shares to book profit.The 30-share index fell by 40.91 points to 16,315.12 points at 1215 hrs following fall in banking, oil &gas and power stocks. The BSE barometer had opened higher by 170 points at 16,525.98 points.The wide-based National Stock Exchange index Nifty fell by 17.60 points to 4,882.10 points. Among the major losers, NTPC fell by 1.96 per cent to Rs 207.10, while Reliance Industries dipped by 1.31 per cent.