Methyl tert-butyl ether (MTBE) is a common fuel additive found in oxygenated gasoline at concentrations up to 15% by volume. Releases of oxygenated fuels from underground storage tanks have resulted in MTBE becoming a potentially long-term groundwater contamination problem because the compound is more soluble, more mobile, and slower to degrade than other gasoline constituents of concern. This is significant because corrective actions for MTBE-containing releases may necessarily differ from those used for other gasoline constituents. This is particularly true for monitored natural attenuation (MNA), an approach that relies on demonstrating that naturally occurring processes such as dispersion, sorption, and biodegradation will control and mitigate groundwater contamination.