The influence of capillary condensation of reagents in porous catalysts for hydrodesulfurization at temperatures below 195degreesC and at pressures around 0.95 MPa was investigated experimentally and by modelling. The rate of reaction of thiophene in a solution of n-heptane was studied in steady and dynamic modes over two Ni-Mo/-gamma-Al2O3 mesoporous catalysts with mean pore diameters differing by 2.6-fold. Pronounced rate hysteresis was observed under thermal cycling for the narrow-pore catalyst, but less so for the wide-pore catalyst. The process was modelled for a mixed-flow reactor under steady and dynamic conditions by means of the Kelvin equation and introducing two kinetic models for liquid and vapour phase to estimate the concentration of reactant in both phases. The model exhibited good agreement with hysteresis results.