In 1993, a Presidential Executive Order was issued requiring that federal agencies purchase lubricants containing at least 25% re-refined base oil. In light of this initiative, we have undertaken a program to characterize the chemical composition of re-refined base stocks, provided by a number of manufacturers, using column chromatography coupled with mass spectrometry techniques. The hydrocarbon-type distribution observed for the re-refined oils provides an index of their relative quality when benchmarked against conventionally processed “virgin” and certain non-conventional, high viscosity index (VI) base oils. Using statistical models which can predict lubricant performance in the ASTM Sequence VE and IIIE Gasoline Engine Tests from base oil compositional features and VI, it was determined that highly paraffinic synthetic and non-conventional base oils provide enhanced performance while re-refined oils generally exhibit predicted behavior comparable to an “average” “virgin” base oil, for most commercially available products. Sequence VE and IIIE test parameter predictions were found to be especially sensitive to the thioaromatic and multiring aromatic content of the base oil under evaluation.