The Sensex today surged by almost 280 points in opening trade. The 30-share index, which lost 74 points in theprevious trading session, shot up by 279 points, or 1.69per cent to 16,725 in the opening trade. The wide-based National Stock Exchange index Nifty regained the 5,000-points level by rising 90 points, or 1.81 per cent, to 5,021 points. Brokers said trading sentiment turned better after theAmbani brothers agreed to cancel existing non-competeagreements, triggering widespread buying, led by RelianceIndustries stocks.