The Sensex gained 72 points in opening trade today on continued buying by foreign funds and retail investors. The 30-share index of the Bombay Stock Exchange, which rallied by nearly 740 points in the previous two sessions, rose by another 72 points to 18,274 points in the first few minutes of trade today. Likewise, the wide-based National Stock Exchange Nifty index moved up by 18 points to 5,474 points.Brokers said sustained buying by funds and retail investors in stocks with strong fundamentals and covering-up of pending short positions by speculators mainly influenced the trading sentiment.