Abstract The effect of plate material on the dispersed-phase holdup in a Karr reciprocating plate column is studied. Existing models cannot predict the observed degradation of the performance of plates as they foul. Experimental data of dispersed-phase holdup have been obtained for a 10 vol% tributyl phosphate/kerosene-phenol-water system in a 50 mm Karr column under various operating conditions using stainless steel, Nylon, and Teflon plate materials. Characteristic velocities decreased with increasing agitation intensity for all systems studied. The characteristic velocities in the column with the Teflon plates were lower than with the other plate materials at the same operating conditions for aqueous-phase dispersion. The characteristic velocities in the column with stainless-steel plates were lower than with other plate materials for organic-phase dispersion. A comparison of the experimental holdups with predictions of existing models assesses the accuracy of the models. The effect of the wetting char...