The essential oils of ten wild growing Ocimum americanum L. of the family Lamiaceae collected from different locations in Uttarakhand, India, were analyzed by capillary gas chromatography (GC) and GC/mass spectrometry (GC/MS). On the basis of chemical composition and cluster analysis, O. americanum was classified into six groups. Group I was significantly rich in methyl chavicol, 1,8-cineole, (E)-γ-bisabolene, β-bisabolene and eugenol, while group II has (E)-γ-bisabolene, aliphatic hydrocarbons, eugenol, β-bisabolene and methyl chavicol as major constituents. Eugenol and (E)-caryophyllene were found in abundant quantity in group III and linalool with methyl chavicol in group IV. Group V contained aliphatic hydrocarbons, eugenol, camphor and 1,8-cineole in high content while camphor and aliphatic hydrocarbons were found in group VI. Linalool was positively correlated with methyl chavicol, while eugenol with (E)-α-bisabolene and β-bisabolene with (E)-γ-bisabolene. The essential oil composition of O. amercanum was found to be affected by variation in soil properties and microclimatic conditions.