Reducing the sulfur content of diesel fuels may require adjusted operation of low-pressure hydrotreater units. A mathematical model for co-hydrotreating of straight run gas oil blended with fluid catalytic cracking naphtha and light cycle oil was developed using an axial distribution of phase equilibrium and effective wetting in the catalytic reactor. The model assumes that hydrodesulfurization (HDS) and hydrodearomatization reactions occur on the catalyst surface which is in contact with the vapor or liquid phase. Kinetic equations of HougenWatson type were used to describe HDS reactions for different classes of sulfur compounds. Model results were validated using the industrial test run data, and very good predictions of overall sulfur conversion and reactor temperature were obtained. Simulations of reactor operation at different pressures, temperatures, and H-2 purities confirm that reaction pressures of around 100 bar and high-purity hydrogen streams are required for almost complete removal of sulfur compounds.