A one-dimensional, plug-flow, trickle-bed reactor model was developed to simulate a steady-state, adiabatic hydrotreating reactor with consideration of vapor liquid equilibrium (VLE) effects. VLE calculations were simultaneously performed at each integration step of the model simulation. The thermophysical properties and mass flow rates of each fluid phase were updated as functions of local variables along the catalyst bed. Substantial differences in hydrodearomatization (HDA) and hydrodesulfurization (HDS) conversions were observed when the simulation was conducted with and without accounting for VLE, indicating the significance of VLE in the hydrotreater simulation. It was found that an increased inlet temperature increases HDS conversion but reduces HDA conversion. Increased pressure increases the reactor temperature and HDS and HDA conversions. Increased gas/oil ratio increases HDA conversion slightly, but does not change HDS conversion significantly. Polyaromatics are the most reactive for hydrogenation, and monoaromatics are the least reactive. Under the operating conditions investigated, both plug-flow and full catalyst wetting criteria are met, although significant vaporization of the liquid oil occurs in the commercial hydrotreating reactor.