Abstract: A piston ring with an upper part ring having an upper ring surface and with a lower part ring having a lower ring surface, and with a ring spring which is arranged between the part rings and acts with spring force upon these radially outward, characterized in that each of the two part rings has, on its circular-ring surface in each case facing the other part ring, a plurality of elevations arranged so as to be separated from one another by depression regions, with plateau surfaces which are parallel to the ring surfaces and are flat-planar or descend and which have in each case, the ring axis of the respective part ring, toward an inner-flank indentation which emanates, oriented parallel to the ring axis, from the plateau surfaces and runs out toward said spring axis, in each case parallel to the upper and the lower ring surface, and which has a quarter-circle-shaped cross section, the radius rv of said inner-flank indentation being 1 to 10% larger than the outer radius of the circle cross section of the comm