We predict the occurrence of commensurability oscillations in the energy loss of a particle moving parallel or perpendicular to a 2DEG subject to a weak density/potential modulation in a quantizing magnetic field. These novel oscillations are associated with the interplay between the length scale of the cyclotron radius at the Fermi energy and that of the modulation period. In the degenerate case, the energy loss is subject to Shubnikov-de Haas–type oscillations associated with the passage of Landau levels through the Fermi energy as magnetic field is varied, and there is also an amplitude envelope manifesting commensurability oscillations. Explicit analytic representations of these features of energy loss are analyzed and evaluated to linear order in the velocity of the moving particle for trajectories parallel and perpendicular to the 2DEG: these energy loss results exhibit phenomenology in close correspondence with that of earlier linear resistivity studies of the density modulated 2DEG.