Until very recently, methyl t-butyl ether (MTBE) was considered non-biodegradable in the subsurface. This has been an impediment in applying remediation by natural attenuation (RNA) as a remedial strategy at MTBE-impacted sites. Although a number of recent studies have demonstrated natural MTBE biodegradation in the field, it is still unknown how prevalent it is and whether the rates of biodegradation are rapid enough to restrict and eventually shrink groundwater plumes. In order to address these questions, BP Amoco, Handex and the EPA have worked together to conduct a groundwater survey at 74 BP retail site in the U.S. Groundwater samples were collected during routine monitoring activities in 1999 and were analyzed for a number of volatile organic compounds including MTBE, t-butyl alcohol (TBA), and BTEXTMB as well as a suite of geochemical parameters including dissolved oxygen, dissolved methane, ferrous iron, total organic carbon (TOC), sulfate, nitrate, alkalinity and pH. Using dissolved methane as a tracer for the plume, first order biodegradation rate constants were estimated for MTBE, TBA and benzene at a number of these sites. There appeared to be a good correlation between strongly anaerobic plume geochemistry and natural MTBE biodegradation in the subsurface.