A simple but general mathematical model has been developed for analysing the rate data for displacement type liquid-liquid PTC reactions in laboratory reactors. The present model accounts for interphase mass transfer effects when present in a regime-independent manner. The model has been validated against published experimental rate data obtained by several workers in a number of reaction systems and in two different laboratory apparatus. The model predicts the time variation of the concentration of all the concerned species in either phase, given the initial composition of the two-phase reaction mixture, the type and the design of the reactor. The model can be used to study the sensitivity of the reaction rate towards the initial charge composition (PTC, organic/aqueous phase reactants, base, salt, if any), agitation speed, and phase hold-up ratio. It can also help to decide if mass transfer effect, in a given reaction under specified experimental conditions, is relevant and if so identify the regime. Finally, the model can be used to estimate the kinetic and distribution equilibria parameters that are of practical importance. This should be a useful tool for the design/scale-up of reactors for industrial PTC-based processes with a displacement reaction as the key step. (C) 2002 Elsevier Science B.V. All rights reserved.