Synthetic lubricant composition of improved oxidation stability

Lubricants comprise a liquid ester oil of general formula XOOCRCOOY where R is a saturated C1-C14 hydrocarbon group, and X and Y are C6-C20 hydrocarbon groups which may or may not be substituted with one or more ether oxygen atoms attached directly to benzene rings only, each of which is either a benzene ring or contains a benzene ring directly attached to the -COO- group, the base oil having dissolved therein one or more organic complexes or salts of the transition metals (including copper) in an amount which gives a metal content of up to 500 p.p.m. based on the total weight of the composition. Metal compounds specified are manganous and cobaltous acetylacetonates, cupric phthalocyanine and cupric stearate. Aromatic amine antioxidants may also be present.