Testing of polymer-thickened multigrade gear lubricants, formulated with hydrotreated basestock, is described. SAE 75W90 lubricants are identified as particularly suitable for Canadian conditions. Shear-stability data and the relationship between viscosity and wear are used to show that good wear control should be expected using either mineral or synthetic based SAE 75W90 lubricants. Increased severity bench tests and extensive field trials support this.Data are given to relate axle efficiency to lubricant viscometric properties, with several multigrade lubricants compared. In a truck road test, an SAE 75W90 lubricant exhibited better fuel economy than a typical SAE 85W90 oil.