Vapor-liquid equilibrium data for the ternary system alpha-pinene + beta-pinene + (S)-(-)-limonene were determined at 80.0 kPa and 101.3 kPa in a modified miniature Othmer still. Parameters of the Wilson, NRTL, and UNIQUAC equations were calculated with the aid of a Nelder-Mead technique to minimize an objective function based on the total pressure. Predictions of the ternary data by parameters determined using binary data were made. The results were compared with the predictions of the UNIFAC method.