Abstract The essential oils of Origanum vulgare L. ssp. viridulum (Martin-Donos) Nyman from Greece, O. libanoticum Boiss. endemic of Lebanon and O. syriacum L. from Lebanon were analyzed by GC and GC/MS. O. vulgare oil contained thymol (61.O-69.1%), O. libanoticum contained methyl thymol (32.8%) and O. syriacum contained carvacrol (88.3%) as major constituents.