Photoautotrophic fatty acid production of a highly CO2-tolerant green alga Chlorococcum littorale was investigated in the presence of inorganic carbon and nitrate at 295 K and a light intensity of 170 mu mol-photon m(-2) s(-1). CO2 concentration in the bubbling gas was adjusted by mixing pure gas components of CO2 and N-2 to avoid photorespiration and beta-oxidation of fatty acids under O-2 atmosphere conditions. Fatty acid content was almost constant for the CO2 concentrations ranging from 5% to 50% under nitrate-rich conditions corresponding to the logarithmic growth phase. After nitrate depletion, the content drastically increased with a decrease in CO2 concentration. HCO3-/CO2 ratio in the culture media was found to be a controlling factor for fatty acid production after the nitrate limitation phase. For a CO2 concentration of 5%, the fatty acid content was ca. 34 wt.% at maximum, which is comparable with other land plant seed oils. (C) 2009 Elsevier Ltd. All rights reserved.