A hydraulic working oil composition for buffers which comprises a lubricating oil as a base oil, (A) a phosphoric acid ester such as dioleyl acid phosphate and/or a phosphorous acid ester such as dioleyl hydrogen phophite, and (B) an adduct of an aliphatic amine such as oleyl amine with an alkylene oxide such as ethylene oxide, the compounds (A) and (B) being the essential components added to said base oil; and, in one embodiment, a process for lubricating buffers which comprises adding said compounds (A) and (B) to said base oil to prepare a hydraulic working oil composition and using the thus prepared oil composition in buffers.