This International Standard specifies a high-pressure liquid chromatographic (HPLC) method, using either an internal standard or external standard, for the determination of the bergapten content in oil of bergamot [Citrus aurantium ssp. bergamia (Risso et Poit.) Wight et Arn. ex Engl.], in oil of lemon [Citrus limon (L.) Burm. f.], in oil of citron (Citrus bigaradia Risso), and in oil of lime [Citrus aurantifolia (Christm.) Swingle and Citrus latifolia Tanaka], all of them fully or partially reduced in bergapten. For essential oils having a bergapten content greater than or equal to a mass fraction of 0,001 %, the internal standard method is applicable. For essential oils having a bergapten content between a mass fraction of 0,000 1 % and 0,001 %, the external standard method is applicable.