The synthesis of three commonly used oxygenated gasoline additives (MTBE, ETBE and IPTBE) in the liquid phase is modeled in a batch reactor using two models: one based on liquid data (the ideal model) and another based only on gas-phase data (the non-ideal model). A Redlich-Kwong-type equation is selected to describe the vapor-liquid equilibrium and the Wang and Sandler mixing rules are used to develop convenient analytical expressions far the residual thermodynamic properties of the non-ideal mixtures. Although based only on gas-phase data, the non-ideal model performs better than the ideal one in the simulation of the liquid-phase synthesis reactions.