Gasoline—or petrol outside North America—is a transparent, flammable liquid fuel refined from crude oil through fractional distillation and mixed with chemical additives to power spark-ignited engines. Its performance is measured by the octane rating, which prevents premature ignition (or "knocking"); while tetraethyl lead was historically used to boost this rating, it is now largely banned for health reasons, though aviation and racing fuels still use it, with modern blends instead relying on oxygenates like ethanol or ETBE. The fuel gained prominence alongside the invention of Germany's Otto engines in the late 19th century, and the 1891 Shukhov cracking process became the first commercial method to extract more gasoline from heavier hydrocarbons. A 160-liter barrel of crude oil yields roughly 72 liters of gasoline, which is actually a complex blend of C4–C12 hydrocarbons (paraffins, olefins, naphthenes, and aromatics) whose composition varies by refinery, feedstock, and season. Crucially, straight-run gasoline (or naphtha) distilled directly from crude lacks sufficient octane for modern engines, so it must be blended with other refinery streams to meet performance standards.