The kinetics of the hydrolysis of heavy hydrocarbons in supercritical water were probed using density function theory (DFT) and molecular dynamics (MD) simulation of the probe molecule dibenzyl ether (DBE). The focus of the study was the effect of solvent on the reaction kinetics. The DFT studies were aimed at the estimation of the kinetic parameters and the transition-state structure, whereas the MD studies were aimed at the estimation of the solubility parameters used in a model of the reaction nonidealities. Both DFT results, with an imposed dielectric constant to represent the solvent polarity, and the MD results, where the solubility parameter was estimated, indicated that the fastest kinetics were attained at the highest polarity. The COSMO-sigma profiles obtained from DFT calculations revealed that the transition state for the reaction was more polar than the reactants. The MD simulation provided estimates of the solubility parameters of reactants and the transition state, which allowed a complementary estimate of the rate of the reaction in a supercritical water solution via transition-state theory. The rates of reaction estimated from DFT and MD calculations at 674 K were in fair agreement with experimental data at low values of the dielectric constant.