Abstract: The claimed invention is an oil pump (18), more particularly for a chain saw (100). The oil pump has a cylindrical pump chamber (20) constructed in a pump housing (19). The pump housing has an intake slot (21) and an outlet slot (23). A pump piston (25) is slidably and rotatably mounted in the pump chamber (20), and is rotatable by means of a gearing (30). The pump piston has a sloping terminal surface (35) that wobbles when the pump piston (25) rotates. The surface area (35) is springably supported against a stop (36). The stop (36), which is located on a rotating element (40), is disposed in the direction of a central longitudinal axis (L) of the pump piston (25) at a fixed distance (R) from the central longitudinal axis (L). The distance (R) predetermines the pump stroke. The angular position of the stop (36) is adjustable by rotating the rotating element (40) about its axis of rotation, thereby causing a phase shift in which the degree of overlap in the opening of the inlet slot and outlet slot change.