ACORGA M5640 (hydroxy-oxime derivative) has been applied as an extraction reagent for vanadium(V) from sulfate media. The extraction system was studied as a function of contact time, temperature, aqueous pH, diluent of the organic phase, and metal and extractant concentrations. The extraction reaction is endothermic and it is dependent on the organic diluent, aqueous pH and extractant concentration. The data have been analysed numerically to determine the stoichiometry of extracted species and their equilibrium constants. It was found that vanadium was extracted into the organic phase by a complex mechanism which involves the formation of two species (VO2R and VO2R. HR, where R represents the extractant). Vanadium stripping by acidic and ammonium hydroxide solutions was also studied. (C) 2003 Society of Chemical Industry.