Test particle calculations are employed to derive van der Waals parameters for methane. It is shown that it is possible to derive these parameters completely based on ab initio calculations. The newly derived parameters are tested in molecular dynamics calculations of liquid methane and the results are compared with the results of existing force fields. It is shown that the newly derived parameters perform better in the prediction of the density, the heat of vaporization, and the self-diffusion coefficient of methane. Scaling of the parameters to account for systematic errors in the employed ab initio method does not generally improve the parameters with respect to the properties calculated. © 1997 by John Wiley & Sons, Inc.