Several simplifications on the dusty gas model were analyzed with respect to the accuracy of the resulting mathematical models in describing the effects of internal mass transport limitations in methanol synthesis. It turned out that all the models, including the simplest one, viz. Thiele modulus concept using pseudo-first-order kinetics, are capable to predict the methanol and water effectiveness factors with a sufficient accuracy. Therefore, application of the simplest Thiele modulus concept is advised, since this model is easily incorporated in complex methanol synthesis reactor models. Moreover, we expect that the Thiele modulus approach can be applied for other complex reaction/diffusion systems, provided that proper linearization of the kinetic model is possible. The experimental data of Seyfert and Luft (1985) on the rate of methanol production for different catalyst sizes can be described with the kinetic expressions of Graaf et al. (1988,1990): using the mathematical mass transport models presented in this paper.