Dried undamaged O. vulgare whole plants (flowers, stems, and leaves) from the six different production areas (100 g each, n = 5) were submitted to hydro-distillation (Chu et al., 2011) in a Clevenger-type apparatus for 6 h. At the end of distillation, the oils were collected, dried with anhydrous sodium sulfate (Na2SO4) prior to analyses, measured, and transferred to glass flasks and stored at 4°C.