  We report on a theoretical study of the commensurability oscillations in a
quasi-two-dimensional electron gas modulated by a unidirectional periodic
potential and subjected to tilted magnetic fields with a strong in-plane
component. As a result of coupling of the in-plane field component and the
confining potential in the finite-width quantum well, the originally circular
cyclotron orbits become anisotropic and tilted out of the sample plane. A
quasi-classical approach to the theory, that relates the magneto-resistance
oscillations to the guiding-center drift, is extended to this case.
