Vapor-liquid equilibrium data for the binary systems alpha-pinene + (S)-(-)-limonene and beta-pinene + (S)-(-)-limonene were determined at 53.3 and 80.0 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. The results were compared with the predictions of the UNIFAC method.