This paper presents fuel property data and associated analytical methodology used in blending test fuels for portions of Phase I and Phase II of the Auto/Oil Air Quality Improvement Research Program (AQIRP). Information presented in this paper supplements the first published report of AQIRP fuel blending results by Pahl and McNally (1).*Fuel blending data are presented covering two segments of Phase I of the Program. The first is a two fuel matrix where the sulfur level is varied at two levels (50 and 450 ppm) through the addition of ditertiarybutyl disulfide. The second is an eleven fuel matrix where the effects of both volatility adjustment and oxygenate addition are investigated. Oxygenates tested include MTBE (methyl tertiary-butyl ether), ethanol, and ETBE (ethyl tertiary-butyl ether). Fuel volatility adjustments are made by changing RVP (Reid Vapor Pressure). Included with the fuel physical property data are individual fuel speciation profiles for all Phase I fuels.Fuel blending data are also presented covering Phase II Auto/Oil research programs that either have been completed or are underway at the time this paper is published. These studies include a second sulfur program where sulfur levels were adjusted at 100 ppm increments between 50 and 450 ppm using sulfur compounds normally found in gasoline, and a single fuel set evaluation of TAME (tertiary amyl-methyl ether) tested in comparison to MTBE.The fuels blending activity also includes efforts to standardize analytical GC (gas chromatography) methodologies used to determine the individual hydrocarbon species within the fuel blend as well as resolving fuel species coelution and identification problems. Certain fuel property test methods are investigated to determine accuracy of various procedures for measurement of benzene, oxygenates, olefins, aromatics and sulfur. Also the impact of oxygenates on the accuracy of standard test methods is investigated along with the effects of depentanization on determination of gasoline aromatics content.