The Sensex gained nearly 220 points in opening trade on the Bombay Stock Exchange today amid a firming trend overseas. The 30-share index of the Bombay Stock Exchange surged by 1.21 per cent, to 18,241.40 within the first few minutes of trade, with oil and gas, realty and banking stocks leading the pack. Similarly, the broad-based National Stock Exchange Nifty index also moved up by 61.75 points to 5,478.95 points today.Meanwhile, Japan's Nikkei index rose by 0.91 per cent and Hong Kong's Hang Seng Index was up 1.38 per cent in early trade today. In the US, the Dow Jones Industrial Average ended 1.25 per cent up yesterday.