Chemical composition of the essential oil hydrodistilled from aerial parts of Sonchus arvensis subsp. uliginosus is reported for the first time. GC and GC-MS analyses of the oil enabled the identification of 114 components that represented 97.4% of the total oil. Main identified constituents were heneicosane (28.4%), (Z)-3-hexen-1-ol (19.0%), (E)-2-hexen-1-ol (11.6%), 1-eicosanol (7.5%) and tricosane (5.3%). Fatty acid derived compounds ("green leaf' volatiles, alkanes, n-alkenes, n-aldehydes and n-alcohols) were by far predominant (89.4%). A much lower percentage of shikimate metabolites (5.0%), carotenoid-derived compounds (1.7%) and terpenoids (0.9%) has also been detected in the oil. Compositions of the essential oils of S. arvensis subsp. uliginosus and other 18 randomly chosen species, characterized by a wide range of essential oil yields, belonging to different plant genera, were compared using multivariate statistical analysis. The results strongly suggest that the main volatiles of essential oil poor species (yields less then 0.1%) are fatty acid- and carotenoid derived compounds, while essential oil rich taxa (essential oil yields much higher then 0.1%) are generally characterized by the specific production of mono- and sesquiterpenoids, and/or phenylpropanoids.