The BSE Sensex tanked 440 points to end at over three-month low of 31,159.81 due to across the board selling by investors ahead of the expiry of September derivatives and weakness in the rupee amid mixed global cues. Extending its falling streak for the seventh straight session -- the longest losing streak since December 22 -- the 30-share index fell by 439.95 points, or 1.39 per cent, to settle at 31,159.81 as RIL, HDFC, HDFC Bank, ITC, SBI and L&T dropped. This is the weakest closing since June 30 when it had settled at 30,921.61.