This project looks at the potential of blending ethanol with natural gasoline to produce Flex-Fuels (ASTM D5798-13a) and high-octane, mid-level ethanol blends Eight natural gasoline samples were collected from pipeline companies or ethanol producers around the United States. Analysis of the natural gasoline shows that the samples are 80-95% paraffinic, 5-15% naphthenic, 3% or less aromatics, and the balance olefins. The paraffins were typically pentane and isopentanes. The benzene content ranged from approximately 0.1 to 1.2 wt % such that blends of E30 or more would meet United States Environmental Protection Agency (U.S. EPA) limits for the benzene content in gasoline. The sulfur content in the natural gasoline ranged between 4 and 146 ppm. Assuming the lowest ethanol content in Flex-Fuel of 51 volume percent (vol %), a natural gasoline blendstock would be required to have 20 ppm sulfur or less for the finished fuel to meet the upcoming U.S. EPA Tier 3 gasoline sulfur limit. The research octane number (RON) (ASTM D2699-13) for the natural gasoline ranged from 67 to 72. Vapor pressure (ASTM D5191-13) ranged from 89 to 101 kPa. Two natural gasoline samples were selected for blending with ethanol. To make a 91 RON fuel (typical of U.S. regular gasoline), natural gasoline had to be blended with 30 vol % ethanol. Because of the high vapor pressure of these blendstocks, over 70 vol % ethanol could be blended into Flex-Fuel while still meeting the class 4 (wintertime) minimum vapor pressure requirement of 66 kPa. For blending of class 1 (summertime) Flex-Fuel, a minimum of 74 vol % ethanol was required to stay below the 62 kPa upper limit on vapor pressure. Modeling of vapor pressure using universal quasichemical functional-group activity coefficients (UNIFAC) and Wilson equation-based approaches provided good agreement with experimental data for most samples.