The BSE Sensex rose for a fourth consecutive session on Wednesday to mark its highest close in nearly four weeks, although amid low volumes, after software exporters such as Infosys gained on continued optimism about US business. The benchmark BSE index rose 0.43 per cent, or 88.76 points, to end at 20,722.97. The broader NSE index rose 0.42 per cent, or 25.65 points, to end at 6,152.75, closing above the technically important 6,150 level. Both indexes marked their highest close since January 24, although volumes were dismal in comparison to Tuesday as India's currency, debt and money markets were closed on Wednesday for a public holiday. Software stocks rose on continued optimism about US business outlook, dealers said. Infosys gained 1.9 per cent, while TCS and Wipro rose 1.5 per cent each. Among pharmaceutical exporters, Lupin rose 2.1 per cent while Dr. Reddy's ended up 1.1 per cent.