This document specifies a high-performance liquid chromatographic (HPLC) method, using either an internal standard or external standard, for the determination of the bergapten content in essential oil of bergamot [Citrus aurantium ssp. bergamia (Risso et Poit.) Wight et Arn. ex Engl.], in essential oil of lemon [Citrus limon (L.) Burm. f.], in essential oil of bitter orange (Citrus bigaradia Risso) and in essential oil of lime [Citrus aurantiifolia (Christm.) Swingle and Citrus latifolia Tanaka], all of them fully or partially reduced in bergapten.