The time-varying lubrication regime is a unique feature of the piston ring-cylinder liner tribosystem. This study proposes a new method for comparing oil film thickness with critical values, consisting of characteristic topo-graphic parameters (Rpk, Rk, and Rvk, etc.), to determine the lubrication regime. The lubrication regime could be determined as hydrodynamic lubrication, micro-plasto-elastohydrodynamic lubrication, micro-plastohydrodynamic lubrication, thin film lubrication, boundary lubrication, or mixed lubrication. The influ-ence of thermal effects and oil-feed conditions on the lubrication regime is discussed. It is found that the friction coefficient alone is not entirely suitable for evaluating the lubrication regime of the piston ring-cylinder liner tribosystem. Nevertheless, this new method is capable of determining the lubrication regime under different operation conditions.