Gives two methods for the potentiometric determination of the carbonyl value of essential oils which contain carbonyl compounds. Method 1 is based on a cold oximation reaction with hydrxoylammonium chloride with exception of citronellal which need a low temperature to avoid cyclization phenomena and acetylization. Method 2 is based on a hot oximation reaction with hydroxylammonium chloride and applies to essential oils whose main constituents are ketones which are general oximable only with difficulty.