The invention proposes a piston ring which has an all-round groove in the region of its inner circumference and interacts with a flexible contact ring. The flexible contact ring rests with elastic deformation against that flank of the piston-ring groove which faces away from the gas pressure and presses the piston ring against the groove flank on the oil-space side. The change in the bearing position of the piston ring due to the inertia forces is not hindered. On the other hand, the additional sealing location prevents the medium to be sealed off from flowing round the piston ring. <IMAGE>
