A roller gerotor device is disclosed including an outer rotor (39) and an inner rotor (31), and a plurality of rollers (37) serving as teeth. The device includes a housing means (11,45,47) defining a first wear surface (67) disposed axially adjacent first axial end surfaces (55,63) of the rotors. The first wear surface cooperates with one of the rotors to define an annular fluid passage (83) and a plurality of fluid grooves communicating with the passage (83) and extending radially outward. At least a terminal portion of each of the grooves (87) is adjacent an axial end surface (59) of each roller member (37) as the rotors rotate. Each of the terminal portions (95) becomes progressively shallower in the direction of rotation of the rotors, thus building up fluid pressure in the fluid groove (87) to prevent gouging or galling of the roller end surface against the adjacent wear surface (67).