The Sensex at the Bombay Stock Exchange eked out a small gain of 19 points, or 0.1 percent, to regain the 18,000-level, and close at 18,012, after volatile trade, amid positive Asian and European markets on Tuesday. The Nifty at the National Stock Exchange rose 8 points, or 0.2 percent, to 5,395.Stock markets in Japan, Hong Kong, Singapore and South Korea gained between 0.1 percent and 0.3 percent.