Abstract A volatile concentrate of Thymus herha-barona was isolated by supercritical C02 extraction with a fractional separation technique. GC/M S analysis of the various fractions obtained at different extraction times and fractionation conditions allowed the identification of the best operating conditions to isolate the volatile extract. A good extraction performance was obtained operating at 90 bar and 50°C for 300 min. The optimum fractionation was achieved by operating at 90 bar and â10°C in the first separator and at 15 bar and 15°C in the second one. The influence of extraction pressure and of extraction time on the extract composition were also evaluated. A comparison between a hydrodistilled oil of Thymus herba-barona and the supercritical extract is also given.