1. A method of treating a pulp suspension with a treatment gas comprising the steps of: (a) adding a quantity of treatment gas to the pulp suspension in the form of finely distributed small bubbles the gas selected from the group consisting essentially of oxygen and oxygen containing gas; (b) after step (a), determining the density of the suspension containing the treatment gas at at least one moment; (c) simultaneously measuring the temperature and pressure of the suspension containing the treatment gas corresponding to the density determined during step (b); (d) calculating the residual gas content of the suspension at the at least one moment at which the density is determined, the calculation utilizing the information determined in steps (b) and (c); (e) calculating the gas consumption as the difference between the quantity of gas added in step (a) and the residual gas quantity calculated according to step (d); (f) controlling the quantity of gas added in step (a) based upon the consumption calculation in step (e) to obtain a desired resultant treatment of the suspension; and wherein steps (b) through (f) are practiced while maintaining the suspension at a substantially contant superatmospheric pressure.