1.1 ,This test method covers the estimation of the mean relative molecular mass of petroleum oils from kinematic viscosity measurements at 100 ,°,F and 210 ,°,F (37.78 ,°,C and 98.89 ,°,C).2 It is applicable to samples with mean relative molecular masses in the range from 250 to 700 and is intended for use with average petroleum fractions. It should not be applied indiscriminately to oils that represent extremes of composition or possess an exceptionally narrow mean relative molecular mass range.