A rigorous steady-state model was written for trickle-bed reactors. The mass and hear transfer resistances both between the gas phase and the liquid phase and between the liquid phase and the catalyst surface are included in the reactor model. The mass transfer is modelled using both the Maxwell-Stefan equations and the effective diffusivity method. The numerical solution of the model is discussed. The reactor model was attached to a flowsheet simulator that provided all the required physical property and phase-behaviour calculations. Finally, an industrial hydrogenation reactor was simulated as an example. The simulation results were used to examine the importance of local mass and heat transfer resistances in the reactor.