Molecular dynamics calculations have mainly used hard-core interactions because of computational simplicity and increased speed. Algorithms for realistic intermolecular potentials have been used in studies of solids and liquids. By combining both techniques, an algorithm which can reasonably study dilute gases with realistic potentials has been achieved. The BoltzmannH-function is calculated for a hard-core and Lennard-Jones gas, and the latter is found to decrease more rapidly to equilibrium.