Chemical reactions with known chemical and physical properties were used for the determination of integral values of the interfacial areas created with an agitator in a gas-liquid contactor. The reactions between oxygen and a sulphite solution and between carbon dioxide and sodium hydroxide solutions were chosen. For the first system the chemical reaction in the liquid boundary layer is proved to be rate determining under our experimental conditions. The existence of two regions is demonstrated : (a) A region without agitation effect. At agitation rates below a minimum agitation rate n(0)D interfacial areas are not affected by the stirring; they only depend on the gas load upsilon(s) and the type of gas sparger. (b) A region with agitation effect. At agitation rates above n(0)D the interfacial areas are linearly dependent on the agitation rate and independent of the gas load and type of gas inlet. The value of n(0)D depends on the tank to agitator diameter ratio and probably is independent of the liquid viscosity. Generally valid correlations for the minimum agitation rates and the interfacial area under fully baffled conditions could be derived for a great number of geometrically similar impellers of different sizes in vessels with diameters ranging from 0.14 to 0.90 m. Although vessels with a diameter larger than 1 m were not investigated the method of correlation seems to give good results for scaling-up. The influence of the physical properties of the liquid remains uncertain.