A bioremediation technology is developed for the clean up of a BTEX contaminated aquifer in Berlin-Spandau area, Germany. The test site is characterized using the existing geological, hydrogeological, and geochemical data. Groundwater monitoring and quantifications of groundwater quality are being carried out since 1997 identifying a quasi stationary BTEX contamination plume with a length of ∼ 250 m. Favorable hydraulic and microbial conditions inhibit the further spreading of the plume. Laboratory batch microcosm experimental results show the expected faster biodegradation rates of BTEX under aerobic conditions as compared to anaerobic conditions. Under anaerobic conditions, NO3- is found to be the most effective electron acceptor to degrade BTEX compounds in groundwater. Under aerobic conditions BTEX disappear completely within 15-64 days depending on the initial BTEX concentration, and no inhibition and toxicity effects were observed during the biodegradation of BTEX compounds. This is an abstract of a paper presented at the 8th International In Situ and On-Site Bioremediation Symposium (Baltimore, MD 6/6-9/2005).