Formation of benzoate from phenol and CO2 in sewage sludge when H2 was present was recently reported. While investigating anaerobic degradation of monochlorophenols, the conversion of phenol to benzoate after reductive dechlorination and before mineralization to CO2 and CH4 was observed. Isomeric fluorophenols were used as phenol analogues to investigate the transformation of phenol to benzoate by an anaerobic, phenol-degrading consortium derived from freshwater sediment. Transformation of 2-fluorophenol and 3-fluorophenol occurred in the presence or absence of phenol and led to the accumulation of fluorobenzoic acids. Identification of the resulting fluorobenzoate products as 3-fluorobenzoate and 2-fluorobenzoate isomers, respectively, together with the nontransformation of 4-fluorophenol indicated that the carboxyl group was introduced para to the phenolic hydroxyl group. (Copyright (c) 1989 by Academic Press, Inc.)