This article presents the findings from a parametric study examining the effect of four contaminants (soot, oxidation, moisture, and sulphuric acid) at varying levels (four for each). It was observed that all contaminants and contaminant levels reduce the conductivity of the oil. Oxidation and soot contaminants produced large increases in viscosity. The wear rate was mainly influenced by acid and soot additions, while the coefficient of friction was increased by all contaminants and contaminant levels. The steady-state charge levels changed for some contaminants. The best correlation of steady-state charge with the other measured tribological parameters of wear rate, friction, and temperature is seen for the series of oxidized oils. The multi-contaminated oil (L4 × 4) shows remarkably little degradation in tribological performance. Analysis of the wear mechanisms shows that soot and oxidation produced abrasion and polishing wear, respectively, while sulphuric acid and moisture produced corrosive wear.