A reactor model to simulate the visbreaking process is developed. The model includes two types of visbreaking reactors: coil and soaker. For the vaporization in the reactor to be taken into account, the vapor liquid equilibrium (VLE) is first determined, and then the reactor model is solved only with the liquid phase because thermal cracking reactions occurring during visbreaking take place in this phase. The variation of liquid and vapor flow rates are also taken into consideration. A reaction scheme based on nine pseudocomponents and kinetic expressions reported in the literature were used. It was found that VLE affects the prediction of reactor conversion depending on the feedstock and the operating conditions. The residue conversion decreases when VLE is considered, which is due to vaporization diminishing the reactor space available for performing the reactions. The model predicts greater mass fractions of gas and naphtha than the experimental values. This is because the model assumes that they are produced by all pseudocomponents heavier than them. It is anticipated that the proposed model can be used in complex refinery planning studies with more reliability than the empirical models available to date.