A mathematical model is developed to analyze the interaction of the internal mass and heat transport with the microkinetics of the heterogeneously catalyzed liquid phase formation of fuel ethers, like methyl tert-butyl-ether (MTBE), from alcohols and tertiary alkenes. A macroporous acidic ion exchange resin is applied as catalyst. Due to the extreme nonideality of the reaction mixtures the multicomponent mass transfer in the macropores is formulated in terms of chemical potential gradients. The sorption of the reactants and the pseudohomogeneous reaction in the gelular phase of the resin are described by a Langmuir-Hinshelwood rate expression in liquid phase activities. The coupled balances are reduced to one differential equation whose solutions are presented in dependence on a generalized Thiele modulus and an enhancement factor for three catalyst geometries. The simulated effectiveness factor and the selectivity are in good agreement with experimental results for MTBE formation in a continuous stirred tank reactor.