The internal fluxes of mixed anaerobic cultures fed 2000 mg l(-1) linoleic acid (LA) plus glucose at 6 initial pH conditions and maintained at 37 C were estimated using a flux balanced analysis (FBA). In cultures fed LA at pH 7, less than 8% of the flux was diverted to CH4. At an initial pH >= 5.5, the quantity of glucose removed was greater than 95%; however, at pH 4.5 and 5.0 the quantity consumed were 38% and 75%, respectively. The FBA output showed that the acetogenic H-2-consumers were responsible for more than 20% of the H-2 consumed. Adding LA and decreasing the pH was ineffective in reducing the activity of acetogenic H2-consumers. As the initial pH decreased, the acetogenic H-2-consuming flux decreased in the presence of 2000 mg l(-1) LA. A maximum H2 yield of 1.55 mol mol(-1) glucose consumed (peak hydrogenase flux (R12)) was attained when the acetogenic H2-consuming flux reached 0.42 mol at a pH of 5.5. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.