Axial dispersion models of two-phase reactors for fluid-fluid systems are proposed in this paper, based on the two-film theory. The mathematical problem of the two-film mass transfer mechanism accompanied by a chemical reaction is treated in a new way, with the aim of using its results to develop reactor design models conveniently. Analytical solutions can be obtained for the case of constant volumetric flow rates in both phases and an irreversible first-order reaction. The mass balance for the gas phase will be a non-linear differential equation if we take the variation of the volumetric flow rate of the gas phase and the pressure drop into account. In this case an iteration procedure is proposed to integrate the differential equation system. The concentration profile, degree of mass transfer, reactant conversion and reactor capacity can be calculated easily by means of analytical or numerical solutions.