The present invention relates to a lubricant composition exhibiting enhanced load-carrying capacity and oxidative/corrosion stability. The lubricant composition of the present invention comprises a major portion of an aliphatic ester base oil having lubrication properties and formed by the reaction of pentaerythritol and an organic carboxylic acid. The lubricant composition further comprises 3-(di-isobutoxy-thiophosphonylsulfanyl)-2-methyl-propionic acid (DITMPA) as an additive comprising from about 0.01 to about 0.40 weight percent of the fully formulated lubricating oil composition as well as yellow metal passivator comprising from about 0.01 to about 0.40 weight percent of the fully formulated lubricating oil composition. The enhanced load-carrying capacity and oxidative/corrosion stability of lubricant compositions containing DITMPA and yellow metal passivator is achieved without deleteriously affecting other salient properties of the lubricant.