Correlation of the average drop size in eight different types of extraction columns, namely, rotating disk, asymmetric rotating disk, Kuhni, Wirz-II, pulsed perforated-plate, Karr reciprocating-plate, packed, and spray columns, is presented. A unified correlation for mechanically agitated columns consists of a two-term additive model involving the ratio of interfacial tension to buoyancy forces at low agitation and the theory of isotropic turbulence at high agitation. This model has further been extended to another two-term correlation, wherein the compartment height and gravitational constant have been introduced to adequately allow for the effect of various variables on the drop size. Only in the case of mixer-settler type Wirz-II columns was the drop size found to be affected by the dispersed-phase holdup. The drop size in unagitated packed columns is determined simply by the ratio of interfacial tension to buoyancy forces, the constant of proportionality in the correlation being a function of the physical properties. The treatment accorded to spray columns is similar to that used for agitated columns, except that the drop Size at high nozzle velocities (jetting region) is controlled by the ratio of interfacial to kinetic energies.