This paper describes a numerical simulation model for prediction of the tribological effects of an oil control ring running against an out-of-round cylinder liner in a heavy duty diesel engine. The model considers the full three-dimensional geometry of the oil control ring and includes the effect of both surface roughness and global deformation. Results that test the model’s ability to do this under stationary conditions are presented. Furthermore, stationary results for prediction of the friction reduction possible by reduced ring tension in combination with reduced out-of-roundness are given. The model predicts the friction for the oil control ring at mid-stroke to be 78% larger in an out-of-round cylinder liner compared to a perfectly cylindrical one.