Vapor-liquid (VLE) and liquid-liquid (LLE) equilibria for the toluene + 1,2-propanediol + water system and the connected binaries have been measured, and the parameters of a thermodynamic model suitable for the description of the system and for the simulation of a multistage separation unit have been derived. The activity coefficients at infinite dilution were determined using GLC, exponential dilutor, and ebulliometry techniques. Comparison was made with previous literature results and from extrapolation of precise VLE results over the composition range determined using a computer-operated differential static apparatus at 303.81 and 343.73 K. In addition, some ternary LLE tie lines at 298.15 K were measured as well as a few ternary vapor-liquid-liquid equilibrium data at other temperatures. Regression analysis of the data was carried out to obtain UNIQUAC temperature-dependent binary interaction parameters. These parameters were used to model the three-phase distillation column with the help of a commercial process simulator.