Abstract Water-distilled essential oils from the aerial parts of two collections of Sideritis congesta, an endemic plant of Turkey growing in Southern Anatolia, were analyzed by GC and GC/MS. Thirty-nine components were characterized in each oil representing 85â90% of the total components detected with β-pinene (34â35%) and α-pinene (24â25%) as major constituents. Key Word Index: Sideritis congesta Labiataeessential oil compositionα-pineneβ-pinene