THE SPARK IGNITION ENGINE HAS REMAINED THE POWER PLANT OF CHOICE for personal transport for almost a century, and the fuel specifically formulated for SI engines is called gasoline (U.S.) or petrol (UK). Gasoline has evolved continuously since it was first produced in quantity to meet the burgeoning demand from mass production of the automobile in the early 1900s. It was first produced from light naphtha batch distilled from crude oil and liquid condensate from natural gas production, and in the early days, had no test methods or specifications at all (see Chapter 2, Liquefied Petroleum Gas). It became a carefully formulated mixture of hydrocarbons and additives, seasonally blended to match local ambient conditions, providing good performance and efficiency for constantly changing vehicle fleet. More recently, gasoline has been formulated to reduce various emissions and minimize the impact of automoblies on urban air quality.