The results of a study of the effect of additives on the thermomechanical stability of sulfonate plastic lubricants are reported. The introduction of both additives and fillers employed to improve tribological properties has been found to improve the thermochemical stability of lubricants. The optimal additive concentrations in sulfonate lubricants derived from petroleum oil blends are determined. Highly alkaline salicylate and succinimide additives in 0.5-1.0 wt. % concentrations in sulfonate lubricants are shown to exhibit an antioxidant effect.