This method is employed for the concentration of sulphide ores. The finely powdered ore is added to water in a tank containing pine oil. The mixture is agitated by blowing a blast of air. The ore particle preferentially wetted by oil come to the surface with froth while impurities which are wetted with water become heavier and settle at the bottom. The oil froth containing mineral particles which floats on froth containing mineral particles which floats on the surface of the water can be skimmed off easily.
Ex : The concentration of copper pyrites, galena are done by this method.