The supercritical fluid extraction (SFE) of aroma compounds from Thymbra spicata was studied. Response surface methodology (RSM) was used to optimize the parameters of the supercritical fluid extraction. Independent variables were temperature (40, 50 and 60 degreesC), pressure (80, 100 and 120 bar) and time (30, 60 and 90 min). Dependent variables were yield, monoterpene, sesquiterpene and oxygenated monoterpene contents. Pressure was the most significant parameter affecting yield. Increase in yield was observed as pressure was increased. There was an inverse effect of temperature on the solubility of oil compounds. The extraction of sesquiterpene and oxygenated compounds were more difficult due to their higher molecular-weight and polarity, respectively, as compared to monoterpenes. The optimum conditions minimising monoterpene hydrocarbons, maximizing yield and oxygenated compounds were found as 41 degreesC, 119 bar and 76.5 min. The response values for these optimum values were 0.67% for yield, 2.75% for monoterpenes, 85.28% for oxygenated compounds and 0.04% for sesquiterpenes. The extract obtained from T. spicata by using supercritical fluid extraction was compared with the essential oil obtained by steam distillation by considering both quantity and quality of the product. The oil yield was higher in steam distillation. In contrast, oil extracted by using SFE contained higher amount of oxygenated compounds. (C) 2003 Elsevier B.V. All rights reserved.