A significant source of volatile organic compounds occurs from fuel evaporation during operation of gasoline-fueled vehicles. This source, known as running loss emissions, has been modelled in the past using the Reid Vapor Pressure (RVP) as the only measure of fuel volatility. A correlation is proposed which relates running loss emissions to measures of fuel volatility at temperatures experienced in use. Ambient temperature, fuel volatility, and, in some cases, drive duration are incorporated into a single correlation. One experimental program shows fuel differences other than RVP have an effect on emissions. Another program is used to estimate in-use running loss emissions. Finally, the in-use emissions are estimated by accounting for ambient temperature, drive duration, and hourly travel fraction.