During the fall, winter, and spring of 1991-1992, a measurement program was conducted in the Denver metropolitan area of Colorado to quantify the technical and economic benefits of oxygenated fuels in reducing automobile carbon monoxide (CO) emissions. Emissions from 80,000 vehicles under a variety of operating conditions were measured and analyzed before, during, and after the introduction of oxygenated fuels in the region. Gasoline samples were taken from several hundred vehicles to confirm the actual oxygen content of the fuel in use. Vehicle operating conditions, such as cold start and warm operations, and ambient conditions were characterized. The variations in emissions attributable to fuel type and to operating conditions were then quantified. This paper will describe the measurement program and its results.The 1991-1992 Colorado oxygenated fuels program contributed to a reduction in carbon monoxide (CO) emissions from gasoline-powered vehicles. The audit demonstrated that most of the reduction is concentrated in a small percentage of vehicles using oxygenated fuels; the remainder experience little or no reduction in emissions. The overall program outlays are approximately $25 to $30 million per year in directly measurable costs, incurred through increased government expenditures, higher costs to private industry, and losses in fuel economy.The measurement program included an analysis to determine the total costs of oxygenated fuels as an air pollution control strategy for the region. Costs measured included government administration and enforcement costs, industry production and distribution costs, and consumer and other user costs.The paper will describe the ability of the oxygenated fuels program to reduce pollution, the overall cost of the program to government, industry, and consumers, and the effectiveness of the program in reducing pollution compared to its costs.