The Sensex opened with a positive gap of 32 points at 12,344. Heavy buying mainly in Reliance Industries saw the index zoom to a new all-time intra-day high of 12,483 - up 172 points from the previous close.A heavy round of selling in the last session saw the index take a sharp U turn and plunge into red to a low of 12,264 - down 219 points from the day's high. However, the index rebounded into the postive zone and ended with a gain of 37 points at 12,348.In the process, the index ended in the positive zone for the fifth straight day, and it has gained 513 points during the period.Thanks to Reliance, the BSE Oil & Gas index surged 2.7% to 5,931. The Bankex advanced 1.6% to 5,717. On the other hand, the Metal index dropped 1.5% to 10,876, and the Capital Goods index declined 1% to 8,795.