The hydrodynamic behavior of countercurrent extractors is described by balancing numbers of incoming and outcoming drops against those formed and destroyed by breakage and coalescence. The laws for these processes are still poorly understood, and no reliable experimental data exist. Special empirical equations were, therefore, derived from measurements in a stirred cell. Using a simplified model a computer program for simulating the variation of the drop-size distribution along the height of a pilot-plant sized stirred column solved the equations for all column stages and preselected characteristic drop volumes. A comprehensive set of holdup and drop-size distribution profiles measured earlier with the same column and o-xylene dispersed in water has been simulated with the average mean deviation of local drop-size distributions not exceeding 20%. Transitional phenomena such as the startup time necessary for obtaining a new steady state after changing the operating parameters and the flooding were successfully predicted.