Influences of high shear viscosity and boundary friction on ASTM Sequence VI and Sequence VI-A fuel efficiency (FE) performances are studied through the use of laboratory screening tests. Statistical analysis of FE and screening test data suggests that optimum screening test conditions are identical for the two engine tests. This being so, a single set of screening test data allows both engine test outcomes to be predicted and the changing influence of the lubricant to be readily perceived.A further investigation is made of the influence of pressure-viscosity coefficient on Sequence VI-A fuel efficiency performance. Values of this property are determined through measurements of elastohydrodynamic oil film thickness and the results included in a further analysis of engine performance. A small but significant influence on fuel efficiency is detected.