Remarkable agreement between molecular dynamics simulations and experi
mental measurements has been obtained for methane for a large range of
intensive variables, including those corresponding to liquid/vapor co
existence. Using a simple Lennard-Jones potential the simulations not
only predict the PVT properties up to 2000 degrees C and 20,000 bar wi
th errors less than 1.5%, but also reproduce phase equilibria well bel
ow 0 degrees C with accuracy close to experiment. This two-parameter m
olecular dynamics equation of state (EOS) is accurate for a much large
r range of temperatures and pressures than our previously published EO
S with a total fifteen parameters or that of Angus et al. (1978) with
thirty-three parameters. By simple scaling, it is possible to predict
PVT and phase equilibria of other nonpolar and weakly polar species.