The dynamic modeling and simulation of a slurry-phase reactor for catalytic hydrotreating of oil fractions obtained from heavy crude oil at 613 K and 5.3 MPa are reported. Compared with previous models, the proposed model incorporates the calculation of Henry constants for the volatile components through a state equation and the variation in superficial gas velocity regarding the G-L mass transfer. The mathematical model is based on the axial dispersion of gas and slurry phases and, therefore, allows approximation of the behavior of the slurry-phase system in a practical way. In order to model the hydrotreating process, different reactions are included such as hydrodesulfurization, hydrodenitrogenation, hydrodearomatization, olefins hydrogenation, and hydrocracking. Kinetic parameters and correlations for hydrodynamic and thermodynamic properties were taken from the literature. The effect of catalyst concentration, temperature, and the variation in gas phase velocity on impurities conversion is analyzed and discussed. Through the simulations, it is pointed out that under some considerations the full axial dispersion model can be simplified through ideal flow models, known as the plug-flow reactor model for the gas phase and stirred tank reactor model for the slurry phase. The need for generating experimental information in order to validate the correlations and the mathematical model is recognized.