In this study the Response Surface Method with a Central Composite Design was applied to an investigation of the effects of ethanol concentration pressure and temperature of ethanol-modified supercritical CO2 extraction on vetiver oil yield and chemical components and optimization of these conditions for the highest oil yield An investigation of whether metals accumulated in vetiver roots would be co-extracted with essential oil by supercritical technology was also conducted The results indicated that both pressure and concentration of added ethanol had significant linear effects on oil yield while temperature and interactive effects were not significant Oil yield increased with both pressure and amounts of added ethanol The optimal conditions were determined to be 190 bar 50 C and 15% ethanol which produced 59% oil yield over three times the hydrodistilled yield and nearly double that of pure SCE (without cosolvent) The operation of ethanol-modified SCE at lower temperature and pressure (100 bar 40 C and 15% ethanol) produced a similar yield (53%) This finding shows an alternative method for extracting high yields of vetiver essential oil without using very high pressure equipment Chemical compositions of vetiver oil extracted within the experimental range of ethanol-modified SCE were not significantly different to those extracted by pure SCE Another interesting result found in this study was that metals accumulated in vetiver roots were not co-extracted with essential oils by either ethanol-modified SCE or pure SCE Therefore SCE vetiver extracts are safe for a variety of applications in terms of heavy metal content in the products (C) 2010 Elsevier B V All rights reserved