Industrially produced Lavender (Lavandula angustifolia L.) and Clary sage (Salvia sclarea Mill.) essential oils are frequently used as ingredients in aromatherapy, traditional medicine, perfumery and cosmetics [1]. The chemical composition of both fresh volatile oils is mainly determined by unsaturated sesquiterpenic hydrocarbons and their oxygenated derivatives, but the main constituents are linalool 1 (22-34%) and linalyl acetate 2 (34-62%). The quality of volatile oils depends a lot on the storage conditions. Their adulteration can be caused by autooxidation, especially of terpenic unsaturated hydrocarbons and the resulted hydroperoxides are harmful, and can cause skin conditions, including cancer [2]. The aim of this study was the determination of the dynamics of mentioned essential oils adulteration on-air exposure, compared to the linalool 1 and linalyl acetate 2 standards, under ambient conditions (25-30ºC) for 20 weeks. During this time, both standards oxidized completely, but in the case of linalool and linalyl acetate in analysed oils the rates of oxidation are insignificantly (~8%) (see Fig.). Also, the results showed that the content of hydrocarbons decreased 16.9%→0.8% (Lavender oil), 7.9%→0.9% (C. sage oil), and that of oxygenated derivative increased 82.5%→98.6% and 82.5%→96.4%, respectively (see Table). The visible difference between the oxidation dynamics of linalool and linalyl acetate from the composition of volatile oils and standard samples is influenced by the competition with mono- and sesquiterpene components for molecular oxygen.