<div class="htmlview paragraph">Fuel volatility affects both the performance of passenger cars and the economics of fuel production. More volatile fuels offer a number of advantages, particularly better low temperature performance and lower cost. The main disadvantage of more volatile gasolines is that they tend to cause vapor lock. The present work was undertaken to obtain current data on the relationships between vapor lock in vehicles and fuel volatility.</div> <div class="htmlview paragraph">Reid vapor pressure alone is not an adequate procedure for controlling the vapor locking tendencies of motor gasolines. In fact, some gasolines of normal vapor pressure have a higher vapor locking tendency than some gasolines of above normal vapor pressure.</div> <div class="htmlview paragraph">A few car models are exceptionally prone to vapor lock. To keep these critical cars out of vapor lock difficulty would require uneconomic fuels. More careful fuel system design is required to avoid the production of critical cars.</div> <div class="htmlview paragraph">The average motor gasoline in many areas of the United States can be made more volatile with safety provided a proper control procedure is used. In some areas the average gasoline approaches the safe level established by field tests.</div>