The Sensex in the Bombay Stocks exchange today crossed the 18000 mark in the noon trade. Gaining over 211 points in opening trade, the Sensex consolidated it gains further and was trading at 18, 046, up by over 317 points a short while ago. Brokers said the investor sentiment was boosted by a firming trend in Asia following a higher close in the US market on the weekend.Japan's Nikkei index was up by 0.86 per cent and Hong Kong's Hang Seng Index by 0.73 per cent in early trade today. In the US, the Dow Jones Industrial Average ended 0.36 per cent higher in the previous session on Friday.