The Bombay Stock Exchange benchmark Sensex gained around 121 points in afternoon trade and was at 17298.5 a short while ago. Nifty was meanwhile up by 36.6 points at 5189.9 at the same time. Sensex had gained about 106 points in early morning trade while Nifty moved up by 37.35 points in early morning trade. Brokers said fresh buying in heavy-weight stocks by funds as well as retail investors amid firming trend on the Asian markets mainly helped the bourses trade in the positive terrain. Stocks of oil and gas, metals, auto and realty sectors were major gainers with increased interest from the traders.