Fuel oxygenates have been added to gasoline since the 1970's to augment fuel octane aslead levels were reduced. Their inclusion in gasoline increased markedly in the mid-1990s in response to the reformulated gas (RFG) program mandated by amendments tothe Clean Air Act (CAA). The CAA mandated the use of oxygenates in areas of the U.S.that did not meet National Ambient Air Quality Standards for carbon monoxide andozone. Such fuel oxygenates as methyl tertiary-butyl ether (MTBE) are used to increasethe oxygen content of gasoline and to reduce carbon monoxide emissions. As a result,MTBE production has increased steadily, ranking fourth overall among organicchemicals, with 15.3 billion liters produced in the U.S. in 1998.Although the RFG program has improved air quality, the expanded use of MTBE ingasoline has, unfortunately, resulted in contamination of surface and groundwaters,many of which serve as sources of drinking water. In 1996, California was one of thefirst states to detect contamination of drinking water sources by MTBE. Similarcontamination has also been documented in Washington and Maine, and, on a nationalscale, by the U.S. Geological Survey (USGS) and U.S. Environmental ProtectionAgency (EPA). Monitoring generally indicates that MTBE contamination ofgroundwater is more prevalent and at higher levels than in surface water.MTBE contamination can occur from a variety of point and non-point sources. Groundwater is particularly vulnerable to MTBE contamination from leaking underground fuelstorage tanks and pipelines, and from landfill sites, dumps and spills. On the other hand,watercraft powered by gasoline engines is the greatest source of MTBE contamination ofsurface water, followed by leaking fuel storage tanks, spills, stormwater runoff andatmospheric deposition. MTBE poses a unique challenge to drinking water agencies because of its ability tocontaminate drinking water sources and its resistance to removal once contamination hasoccurred. Unlike other hydrocarbon constituents in gasoline, MTBE's physical andchemical properties (high solubility in water and poor adsorption to soils), allows it toeasily mix and move with surface and groundwater flow. These same properties impedethe removal of MTBE from water by natural attenuation processes (volatilization,sorption, photo- and bio-degradation) and by the treatment processes commonly used bydrinking water agencies. Agencies that rely on groundwater as sources of drinking water are most vulnerablebecause MTBE contamination occurs with greater frequency and at higher levels ingroundwater. For example, seven wells comprising almost half the water supply of theCity of Santa Monica were taken out of service when MTBE levels as high as 600 partsper billion (ppb) were detected. Although agencies using surface drinking water sourcesare less at risk to operational impacts from MTBE contamination, they may face thechallenge of balancing source water protection with public recreational access. Theexperience of the East Bay Municipal Utility District of Oakland, California, in addressing thischallenge is used to illustrate a practical and successful approach to this problem. Includes 6 references, figures.