On average 36 percent of the benzo[a]pyrene in an automobile's exhaust gas comes from the benzo[a]pyrene originally in the gasoline. Between 0.1 and 0.2 percent of the benzo[a]pyrene in the gasoline survives the combustion process and is recovered from the exhaust; 5 percent accumulates in the crankcase oil. Some of the benzo[a]pyrene in the gasoline is converted into other polynuclear aromatic hydrocarbons and other more polar compounds. For our experiments we used commercial gasoline containing benzo[a]pyrene at 1.0 part per million to which was added benzo[a]pyrene-8,9-(14)C at 1.1 parts per million as a radioactive tracer.