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Continuing interest in energy conservation and friction reduction, driven primarily by environmental concerns, provides opportunities to develop energy saving lubricants. The greatest potential energy savings come from reductions in hydrodynamic friction as typified by main and connecting rod journal bearings in automotive engines. The main approach to minimise friction losses in these bearings is to reduce the lubricant viscosity. However, this approach will inevitably reduce oil film thickness and impose even higher stresses on the lubricant. The problem is compounded by the use of multigrade oils, which contain relatively high molecular weight polymeric components, and exhibit both temporary and permanent shear thinning. Thus these lubricants exhibit non-Newtonian flow behaviour under the extreme conditions imposed by engine bearings.