For many years, the primary consideration for determining motor gasoline volatility specifications has been good car performance, i.e., fast start-ups, freedom from vapor lock, and good driveability. Now, for late-model cars, there is a new consideration for volatility control. This is exhaust emissions. Fuel volatility has been found to have a significant effect on the exhaust emissions of many late-model vehicles. A decrease of 5 psi RVP from current levels increased exhaust CO an average of 28% at 70°F and 22% at 30°F in a group of eleven cars. Exhaust hydrocarbons were increased an average of about 5% at both temperatures. Now, before lowering fuel volatility, it is important to consider the effect the change will have on exhaust emissions as well as car performance.