The BSE benchmark Sensex extended gains for the second straight day by adding 18 points in early trade today on selective buying by funds and retail investors ahead of the RBI's monetary policy review for 2012-13. The 30-share index, which had gained 56 points in the previous session, added another 18 points, or 0.11 per cent to 17,169.The wide-based National Stock Exchange index Nifty also traded marginally up by 4 points, or 0.08 per cent, to 5,231.In the Asian region, the Japan's Nikkei was up 0.06 per cent, while Hong Kong's Hang Seng shed 0.06 per cent in the morning trade today. The US Dow Jones Industrial Average ended 0.56 per cent higher in yesterday's trade.