AbstractThe species which grow wild and are used as oregano in Greece are Coridothymus capltatus (L.) Reichenb. fil., Satureja thymbra L., Origanum onites L. and O. vulgare L. Because of their economic importance, we studied their distribution in Greece and their essential oils. By examining various populations from all over the country, intraspecific variability was detected as to essential oil contents and to the carvacrol content of the oils, the main component responsible for their use as oregano. The species were evaluated on the basis of their oil and carvacrol contents. O. onites proved to be the most stable species, that was always rich in carvacrol, whereas O. vulgare was the most variable one. O. vulgare subsp. hirtum (Link) letswaart was very rich in essential oil; in some cases a content of about 8% was found and a carvacrol content ranging from 2.4% to 95%. O. vulgare subsp. vulgare contained only small amounts of essential oil (<0.3%) and amounts of carvacrol below 0.1 %. For these reasons the latter subspecies should not be used as oregano, although it belongs to the genus Origanum.