In this communication, the results of computer simulations of the vapor-liquid equilibria of n-pentane and n-octane are reported. We have used a novel Monte Carlo technique to simulate directly phase equilibria of chain molecules. The calculations were performed for a united-atom model using the Lennard-Jones parameter set of Jorgensen and co-workers.¹ Comparison of the calculated phase diagrams with experimental data shows very good agreement, in particular for the shorter alkane.