A journal bearing rig has been used to determine the viscosity of ten multigrade oils under hydrodynamic lubrication conditions at a mean shear rate of 5 × 105 s-1 and a temperature of 150°C. These conditions closely approximate the shear rate and temperature likely to be encountered when an oil is subjected to severe service in engine bearings.The same rig has been used to study the effect of lubricant viscosity on wear under boundary lubrication conditions at 150°C. Bearing wear was determined by weighing the bearing shells. The results obtained under static load showed that for single-grade lubricants wear increased markedly with decreasing viscosity. However, for a number of polymer-containing oils including 10W30 and 10W40 multigrades, similar experiments showed that wear was not influenced by high-shear viscosity at least not in the region between 2.1 and 4.9 mPa.s. Attempts to explain this behaviour should take into account an additional contribution to load-bearing capacity from the elastic properties of polymer-containing multigrade oils, or protection of the metal surface by polymer adsorption.