A 288 hour cyclic durability test has been developed Co determine bearing wear in the big-end bearings of a 2.8 litre V-6 gasoline engine. Bearing wear for a 5W30 oil with a high-temperature, high-shear (HTHS) viscosity of 2.5 mPa.s is at least as low as that for SAE 30 to SAE 50 monograde oils. Minimum oil film thickness, (MOFT)0, under steady-state operating conditions has also been determined in the big-end bearing of the same engine. There is a critical value of (MOFT)0 below which catastrophic wear occurs. Correlations between (MOFT)0 and high-temperature, high-shear-rate viscosity show that the latter parameter is deficient as a measure of lubricant load bearing capacity. It is concluded that measurement of (MOFT)0 in an operating engine is the optimum test for the routine assessment of lubricant performance in a journal bearing.