Concern over the impacts of changes in gasoline composition on refueling emissions stimulated a search for a simple technique to provide estimates of related fuel parameters. Accordingly, a mathematical computer model was developed based on the assumption that gasoline liquid-vapor equilibria can be predicted with reasonable accuracy from Raoult's law for ideal mixtures. Gasoline fuel parameters such as vapor pressure (including Reid Vapor Pressure, RVP), refueling loss, OH reactivity in forming atmospheric ozone pollution, and other fuel characteristics were addressed. The assumptions made and model results were validated by comparison to measured fuel parameters from 9 unleaded gasoline fuels. Extrapolations were made to illustrate fuel temperature and vapor/liquid ratio effects. Calculated RVP levels were found to be within 5% of measured values for the fuels evaluated. A complete listing of the model's source code written specifically for a Fortune 32 : 16 microcomputer is provided.