Base oil effects on oxidation, deposit formation, and wear in the ASTM Sequence IIID and Sequence V-D engine tests were studied. Key base oil variables were found to be base oil saturates, sulfur, nitrogen, and olefin content. No one single base oil variable adequately predicts the onset of Sequence IIID rapid viscosity increase although a linear combination of variables yielded good performance predictions. Sequence V-D deposits correlate modestly well with any of several parameters, but a four variable linear equation produces an excellent prediction model. Base oil composition was found to have no effect on valve train wear in either Sequence IIID or Sequence V-D with the additive packages used.