A detailed analysis of Bupleurum fruticosum oil was carried out by combination of GC (RI), GC/MS, and 13C-NMR analyses. After fractionation by column chromatography, 34 components accounting for 97.8% of the oils were identified. The main component was beta-phellandrene (67.7%), followed by sabinene (9.3%), and limonene (5.6%). The evolution of the chemical composition according to the stages of development of the plant was investigated as well as the composition of leaf, twig, and flower oils. A solvent-free microwave extraction (SFME) of aerial parts was carried out and the composition of the extract compared with that of the essential oil. Finally, 57 oil samples isolated from aerial parts of individual plants, collected all around Corsica, were analyzed, and the data were submitted to statistical analysis. Although the contents of the main components varied, only one group emerged, accompanied with some atypical compositions.