In this paper, a previously developed first-order hard sphere perturbation theory of a ternary fluid mixture (Fotouh and Shukla, 1996, Chem. Engng Sci. 51, 4923-4931) is applied to predict excess properties of a real ternary fluid mixture using a theoretically consistent combination rule. We consider a ternary fluid mixture N-2/Ar/CH4, for which experimental data for excess properties are available and which can be modeled adequately using the simple Lennard-Jones potential function. Comparisons of theoretical results with experimental data show a very good performance of perturbation theory for different pressures and compositions of the mixture. Also, we checked the accuracy of a recent form of van der Waals one-fluid theory based on the most accurate equation of state for pure Lennard-Jones fluids. Van der Waals one-fluid theory is found to be equally reliable in describing excess properties of such a moderately nonideal mixture.