The purpose of this report is for EPA OTAQ (Office of Transportation and Air Quality) to give an initial summary of EPA ORD (Office of Research and Development) work on the composition of hydrocarbon emissions from gasoline, specifically the head space components above gasoline in an enclosed fuel tank. EPA ORD will formally publish this work in a scientific journal but, until that is done, this report will provide details on that work since it is related to EPA regulatory packages such as air quality modeling done for the Renewable Fuel Standards and Light-Duty Vehicle Greenhouse Gas Standards. Headspace vapors are those hydrocarbon compounds in gaseous form above a gasoline sample in an enclosed space such as a fuel tank, frequently a fuel storage tank used in the distribution for gasoline. Some of these vapors are emitted to the atmosphere in transport, storage, and utilization of gasoline. The numerous hydrocarbon compounds (about 120 individual hydrocarbons) represent the more volatile and lower molecular weight components of the gasoline. In recent years and even more so in the future, ethanol, as a renewable fuel component, is blended with gasoline generally at the 10% level, which results in 90% gasoline with 10% ethanol. This fuel mixture of 90% gasoline and 10% ethanol (in denatured form) will be referred to as E10 while 100% gasoline with no ethanol added will be referred to as E0. Also, blends of 85% ethanol and 15% gasoline (E85) can be used in specially designed flexible-fueled vehicles but new headspace profiles with E85 have not yet been obtained in this project for E85.