The essential oil contents and compositions of the leaves and inflorescences of Ocimum basilicum L. (four chemotypes), Ocimum kilimandscharicum Guerke (two chemotypes), Ocimum americanum L. and Ocimum grattisimum L. were analyzed and compared using gas chromatography (GC) and GCâmass spectrometry (GCâMS). Essential oil content on a fresh weight basis varied from 0.60% to 1.00% in leaves and from 0.28% to 0.85% in inflorescences of different Ocimum species/chemotypes. A total of eighty-six components, constituting 96.4â99.2% of the leaf oil and 88.0â99.3% of inflorescence oil, were identified. Phenylpropanoids (methyl chavicol and eugenol) and monoterpenoids (citral, camphor, linalool, 1,8-cineole, limonene and (Z)-Î²-ocimene) were among the major constituents identified in their essential oils. Chromatographic results and subsequent hierarchical cluster analysis showed that the distribution of components, both qualitatively and quantitatively, varied considerably in leaf and inflorescence essential oils of the studied Ocimum species and their chemotypes.