Disclosed are synergistic antioxidant compositions composed of (1) amine salts of alkyl phosphates and (2) ethylenediamine, ammonium or metal salts of alkylarylsulfonates. The antioxidant compositions are useful for formulating zinc-free antiwear hydraulic fluids and gear lubricating oils in conjunction with thiophosphate type antiwear agents, corrosion and rust inhibitors.