Drop size distribution and Sauter mean drop diameters have been evaluated in an Oldshue-Rushton pilot plant extractor for three various liquid-liquid systems as a function of phase flow rates and intensity of agitation. The Sauter mean drop diameter and drop size distribution were found to depend largely on the speed of agitation, physical properties of liquid systems and direction of mass transfer, but, only partially dependent on the phase flow rates. The experimental data are then fitted by means of a probability density function, namely normal and log-normal function. The mathematical approach is used to determine the constant parameters in these functions and to provide the fit of the experimental data with them. Moreover, an empirical correlation is proposed for estimation of the Sauter mean drop diameter in terms of operating variables, column geometry and physical properties. Good agreement between the prediction and experimental results and the data in the literature was achieved for all investigated operating conditions. (C) 2015 Elsevier B.V. All rights reserved.