We have investigated certain aspects of the dynamics of methane monolayers physisorbed on graphite. In particular, phonon frequencies have been calculated by applying the self-consistent harmonic approximation to a two-dimensional array of methane molecules arranged as stable tripods on a triangular lattice. The methane–graphite interaction was not considered explicitly, and only three degrees of freedom per molecule were taken into account: two translations parallel to the surface and rotation about the axis normal to the surface. A new intermolecular potential proposed by Righini and present authors was employed. It was found that the translation–rotation coupling plays an important role in determining the anharmonic frequency shift. The results are in good agreement with a recent neutron incoherent inelastic scattering experiment in which the momentum transfer is parallel to the graphite surface. The two main peaks observed around 9 and 5 meV are assigned to librational and translational modes, respectively.