Gasoline or petrol is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When formulated as a fuel for engines, gasoline is chemically composed of organic compounds derived from the fractional distillation of petroleum and later chemically enhanced with gasoline additives. It is a high-volume profitable product produced in crude oil refineries. The fuel-characteristics of a particular gasoline-blend, which will resist igniting too early—and cause engine knocking and reduce efficiency in reciprocating engines—are measured as the octane rating of the fuel blend; the gasoline blend with the most stable octane rating then is produced in several fuel-grades for different types of motor. Tetraethyl lead and other lead compounds were once widely used as additives to increase the octane rating, but are not used in modern automotive gasoline due to the extreme health hazard, except in aviation, off-road motor vehicles, and racing car motors. The additive continued to be used in low-income countries for decades after others had phased it out, leading the UN Environment Programme (UNEP) to launch a campaign to eliminate its use. This campaign finally led to Algeria being the last country to stop its use in 2021. Gasoline can be released into the Earth's environment as an uncombusted liquid fuel, as a flammable liquid, or as a vapor by way of leakages occurring during its production, handling, transport and delivery. Gasoline contains known carcinogens. Gasoline is often used as a recreational inhalant and can be harmful or fatal when used in such a manner. When burned, one liter (0.26 U.S. gal) of gasoline emits about 2.3 kilograms (5.1 lb) of CO2, a greenhouse gas, contributing to human-caused climate change. Oil products, including gasoline, were responsible for about 32% of CO2 emissions worldwide in 2021. On average, U.S. petroleum refineries produce about 19 to 20 gallons of gasoline, 11 to 13 gallons of distillate fuel diesel fuel and 3 to 4 gallons of jet fuel from each 42 gallon (152 liters) barrel of crude oil. The product ratio depends upon the processing in an oil refinery and the crude oil assay (see § Etymology). Source: Wikipedia (en)