Reformulated gasoline (RFG) was introduced at retail gasoline stations in the six county Southeastern Wisconsin severe ozone non-attainment area in December, 1994, preceding the mandated January 1,1995, introduction date. By late January and early February a substantial local outcry encompassing health complaints and excessive fuel economy reduction complaints had materialized.In response to the negative public reaction, the Wisconsin Department of Natural Resources (WDNR) and the US Environmental Protection Agency (EPA) jointly conducted an investigation of the excessive fuel economy reduction anecdotes in a two week, 15,000 mile on-road test study. The University of Wisconsin-Milwaukee Center for Alternative Fuels (UWM) performed a follow up investigation of the excessive fuel economy reduction anecdotes at the UWM emissions laboratory under controlled, repeatable conditions.The objectives of the UWM RFG study were to investigate the possibility of excessive fuel economy reduction anecdotes by measuring the fuel economy of various vehicles, using different RFG types and grades and comparing the RFG varieties containing methyl-tertiary-butyl-ether (MTBE), ethyl-tertiary-butyl-ether (ETBE) and ethanol (EtOH) against conventional gasoline.Nine vehicles were used in the study including both open-loop control system vehicles and various technology closed-loop vehicles. Eight fuels were used in the study: regular (87 octane) and mid-grade (89 octane) of each type of RFG and conventional gasoline.The average fleet fuel economy statistics for both the WDNR/EPA and the UWM investigations approximated the nominal 2-3% fuel economy reduction expected based on the energy content reduction of RFG in relation to conventional gasoline. Frequency distributions of the fuel economy results showed a wide deviation about the average. The lower 5 and 10 percentiles of the distribution exhibiting the most severe fuel economy reduction showed excessive fuel economy reduction up to 16% and 14%, respectively. The distribution substantiated that a portion of the anecdotal fuel economy complaints may be valid.Consistent excessive fuel economy reduction or gain correlations were not found between the various driving cycles, vehicle control technology, and RFG blends.