Abstract: Pistons and associated piston rings are described for use in internal combustion engines. The piston and piston ring comprise an annular piston ring groove having two radially extending walls and an axially extending wall; a compression ring received in the piston ring groove for sealing engagement with an associated cylinder wall or liner; a recess in the compression ring extending in an outwardly direction; an auxiliary sealing ring in permanent but deflectable contact with the axially extending wall of the annular piston ring groove and penetrating the recess in the compression ring; the arrangement being such that the auxiliary sealing ring does not physically limit the extent of movement of the compression ring in the annular piston ring groove. Pistons are described where two conventional compression rings are replaced by one. Test results are also presented.