Higher alcohol synthesis (HAS) from syngas over a Cu Symbol of the Klingon Empire Co based catalyst was investigated under supercritical hexanes conditions. The effects of hexanes/syngas molar ratio, H-2/CO molar ratio, and gas hourly space velocity (GHSV) on gas-phase HAS and supercritical hexanes-phase HAS (SC-HAS) were investigated. The CO conversion remained relatively constant with increases in the hexanes/syngas molar ratio, whereas the CH4 selectivity decreased. Higher alcohol productivity was found to increase monotonically with an increase in the hexanes/syngas molar ratio. Productivity of higher alcohols increased with an increase in the H-2/CO ratio under the gas-phase conditions. An opposite trend in higher alcohol productivity with H-2/CO was observed in SC-HAS. Further experiments were performed using argon as the reaction medium for comparison with the supercritical hexanes medium results. The enhanced higher alcohol productivity observed in this system can be attributed to improved extraction of alcohol products from the catalyst pores under the supercritical conditions. (c) 2014 American Institute of Chemical Engineers AIChE J, 60: 1786-1796, 2014