Catastrophic failures of fuel pumps used to transport ethanol have occurred in various facilities. Failures occurred in as little as 50 hours on pumps with a 2000 hour life expectancy. Post-failure inspection of the pumps showed corrosive pitting of the metal in the areas of sliding contact. Several potential causes, including cavitation, thermal expansion of pump parts, and fuel contaminants such as acetic acid were ruled out. Fuel samples from facilities with high pump failure rates passed all D 4806 specification tests for fuel-grade ethanol, including titratable acid by D 1613. However, pH readings as low as 2.0 indicated potentially corrosive fuels. Controlled tests on pumps and corrosion tests showed that pump failures correlated with fuel pH. Corrosive fuels were found to contain ethyl sulfate, which correlated with fuel pH. It appears that ethyl sulfate originates from sulfur dioxide, which is used as an antioxidant and antiseptic in the production of ethanol.