AbstractSurface excess isothermers were determined and interpreted for systems containing 2‐hydroxy‐5‐t‐nonylbenzaldehyde oxime (1), 2‐hydroxy‐5‐t‐octylacetophenone oxime (2) and 2‐hydroxy‐5‐t‐octylbenzophenone oxime (3). These surface excess isotherms were used to predict reaction orders with respect to hydroxyoximes for various versions of interfacial process. Agreement with the experimental data was observed both for the interfacial and bulk aqueous mechanism. The surface activity of extractants cannot be recognized as the sole evidence for the interfacial mechanism of extraction. More experimental kinetic data are needed in order to determine the effect of hydroxyoxime concentration upon the reaction order. According to the interfacial mechanism, with the formation of the stable 2:1 complex as the limiting step the reaction order in hydroxyoxime equal to 1 is observed over a large range of hydroxyoxime concentration, but increases to 1.5‐2.0 fo