Single inorganic carbon source was used for production of chemicals and fuels via fermentation processes. Clostridium ljungdahlii, a strictly anaerobic autotrophic bacterium, was grown on synthesis gas to produce acetate and ethanol from gaseous substrates. C. ljungdahlii was grown on a various concentrations of carbon monoxide with synthesis gas total pressures of 0.8-1.8 atm with an interval of 0.2 atm. The cell and product yields were 0.015 g cell/g CO and 0.41 acetate/g CO2 respectively. Formation of acetate was steady and the production trend was about the same for all of the gases initial pressure and at constant cell density. The ethanol concentration was enhanced by the initial presence of hydrogen and carbon dioxide in the liquid phase. There was no substrate inhibition while C. ljungdahlii was grown in the batch fermentation, even at high system pressure of 1.6 and 1.8 atm. A desired product molar ratio of ethanol:acetate (5: 1) was achieved with total gas pressure of 1.6 and 1.8 atm. (c) 2005 Elsevier Inc. All rights reserved.