An analysis and a method of computation of the oil film thickness between the piston ring and cylinder liner of an internal combustion engine is presented here. A three-dimensional form of Reynolds' equation is used to enable consideration of film thickness variation in the circumferential direction. Various ring face profiles are considered in the analysis. The “tipping” of the ring about the piston axis is also included in the calculation. The solution of the resultant lubrication equation is achieved by using a finite difference approximation.