Benzene is a known carcinogen and benzene contamination of groundwater presents a threat to those reliant on aquifers for drinking water. Aerobic benzene biodegradation is well understood yet the pathway for anaerobic benzene degradation is unknown. This study examined the enrichment of anaerobic benzene-degrading microbial communities and reports a maximum benzene degradation rate of 104 muM/d and a maximum specific rate of benzene degradation 5.2 muM/mg protein/day. Methylation of benzene to toluene was previously observed yet in this study the methanogenic culture observed did not produce toluene during benzene degradation, and degraded existing toluene. Diethyl ether extraction coupled to GC/MS analysis using a DB WAX column was not effective in determining if 13C carbonate was the source of the methyl group for benzene methylation to toluene. This study reinforces that a great deal remains unknown about these enrichment cultures and changes in degradation rates do not always follow expected patterns.