Abstract: A hydrocarbon fuel, especially a copper-sweetened aviation jet fuel, contains a metal deactivator which is an oxime of either an orthohydroxy aromatic ketone or .alpha.-hydroxy aliphatic ketone, or an imine of a diamine with an ortho hydroxy aromatic ketone, an alkyl substituted ortho hydroxy aromatic aldehyde or a -diketone. Preferred materials include oximes of 2-hydroxy-5-t-butyl benzophenone and 2-hydroxy-5-nonyl acetophenene and di-imines of ethylene and propylene diamines with benzoyl acetone, 5-t-octylsalicylaldehye or 2-hydoroxy-5-methyl butyrophenone.The metal de-activator is added in conventional proportions, typically about 5 to 10 ppm (by weight) to the fuel which may contain either conventional additives such as anti-static, anti-icing and corrosion inhibiting additives.