from 0 wt to about 20 wt and preferably from 0 wt to about 15 wt of a triaryl phosphate the composition of the present invention includes a minor but effective amount of both an alkali metal perfluoro phosphate and a mono epoxy cyclohexane carboxylate specifically the composition will include from about 0 01 wt to about 0 5 wt based on the weight of the composition of an alkali metal perfluoro phosphate or mixtures of alkali metal perfluorophosphate alkali metals of course include lithium sodium potassium rubidium and cesium preferably the alkali metal perfluorophosphate is potassium perfluoro phosphate the composition of the present invention also will include a mono epoxyclyclohexane carboxylate specifically the composition will include from about 1 wt to about 10 wt of a mono epoxide represented by the formula where r is selected from the group consisting of alkyl groups having from 1 to 10 carbon atoms and u2014 ch 2 n u2014 or 1 where r 1 is an alkyl group of 1 to 10 carbon atoms and n is an integer of from 1 to 3 preferably r is a branched alkyl group of 4 to 8 carbon atoms and more preferably r is a 2 ethyl 1 hexyl group in a preferred embodiment the hydraulic fluid compositions of this invention further comprise an antioxidant or mixture of antioxidants in an amount effective to inhibit oxidation of the fluid or its components suitable antioxidants include polyphenols trialkyl phenols and di alkyl phenyl amines representative examples include bis 3 5 di tert butyl 4 hydroxy phenyl methane e g hitec u00ae 4702 from ethyl corp 1 3 5 trimethyl 2 4 6 tris 3 5 di tert butyl 4.