Ethanol usage in the United States has increased due in part to the elimination of methyl tert-butyl ether from the fuel supply and to the mandates of Congress. Two samples, one each from a wet mill and a dry mill ethanol plant, were obtained before denaturing. Each of these samples contained mostly ethanol, but also low concentrations of water, methanol, and higher molecular weight alcohols (up to five carbons). The wet mill sample also contained ethyl acetate and an ether, 1,1-diethoxyethane. The allowable denaturants for fuel ethanol are similar to gasoline. Since the denaturants are immiscible with water, the ability of the denatured fuel ethanol to absorb water is limited. Experiments with E95 and E85 showed that these both began to phase separate when about 15% water was added to the E95 or E85. The gasoline was released gradually as water was added to the fuel. For E95, there is a smaller amount of gasoline in the fuel (2% to 5%) so less gasoline can be released. The changes in volume when water and ethanol or water and E85 are mixed displayed a deficit of 3% at maximum. The byproducts of fuel ethanol production are less soluble, sorb more, diffuse less readily, and are less volatile than ethanol. Its likely, however, that the increased ethanol concentration in water will increase the solubility of the byproducts, as it does the petroleum hydrocarbons. The production byproducts compose less than 1% of the mass of the fuel. Releases of fuel ethanol will be dominated by the ethanol.