This investigation focused on the qualitative and quantitative composition of essential oil compounds of European Origanum vulgare. Extracts of 502 individual O. vulgare plants from 17 countries and 51 populations were analyzed via GC. Extracts of 49 plants of 5 populations of Israeli Origanum syriacum and 30 plants from 3 populations of Turkish Origanum onites were included to exemplify essential oil characteristics of "high-quality" oregano. The content of essential oil compounds of European O. vulgare ranged between 0.03% and 4.6%. The monoterpenes were primarily made up of sabinene, myrcene, p-cymene, 1,8-cineole, β-ocimene, γ-terpinene, sabinene hydrate, linalool, α-terpineol, carvacrol methyl ether, linalyl acetate, thymol and carvacrol. Among the sesquiterpenes β-caryophyllene, germacrene D, germacrene D-4-ol, spathulenol, caryophyllene oxide and oplopanone were often present in higher amounts. According to the proportions of cymyl-compounds, sabinyl-compounds and the acyclic linalool/linalyl acetate three different main monoterpene chemotypes were defined. The cymyl- and the acyclic pathway were usually active in plants from the Mediterranean climate whereas an active sabinyl-pathway was a characteristic of plants from the Continental climate.