The yield and composition of essential oils from leaves, stems, umbel rays and also from whole aerial parts of Bupleurum gibraltarium Lam. (Apiaceae) were determined during the pre-flowering, full flowering, late flowering, and fruiting vegetative periods. A fruit sample was also studied for comparative purposes. Leaves (0.8â1.8% yield) and stems (0.3â0.7%) reached their maximum oil content during the late flowering period, whereas umbel rays (2.2â3.7%) reached it in full flowering. Oil samples were analyzed by capillary GC and GC/MS components which were found in amounts greater than 2% were selected to carry out a seasonal study. In the leaf oils, sabinene (12.0â33.9%) and limonene (7.8â23.4%) were the main components, the sabinene level being minimum in full flowering and maximum in fruiting. In stem oils, sabinene (4.7â21.6%) and 2,3,4-trimethylbenzaldehyde (9.3â13.6%) were the main components, the sabinene level being minimum in pre-flowering and maximum in full flowering. In umbel ray oils, sabinene (20.7â43.1%) was the first component in all the phenological periods, followed by Î±-pinene (7.3â28.2%). Both monoterpenes increased their levels in late flowering and reached minimum amounts in fruiting. Â© 2006, Taylor &amp; Francis Group, LLC. All rights reserved.