In an infinite elastic medium dilatational waves exhibit much more nonlinear distortion than do shear waves, but such behavior cannot be assumed when a boundary, such as a free surface, is present. Because of the process of mode conversion, a dilatational (P) wave that has already undergone significant distortion prior to its incidence at the boundary must impart its distortion to both the reflected P and vertically polarized shear (SV) wave. The problem of oblique incidence at a free surface was previously considered by us [1,2]. The present paper generalizes that analysis by permitting the boundary conditions at the planar interface to be arbitrary, and also by considering critical and supercritical angles of incidence.