Gasoline, written as 汽油 (qì yóu), is a volatile, flammable liquid fuel derived from petroleum and used primarily in internal combustion engines—especially in cars, motorcycles, and small machinery. The character 汽 (qì) means 'vapor' or 'steam', reflecting gasoline’s gaseous state when vaporized for ignition; 油 (yóu) means 'oil' or 'grease', indicating its oily, hydrocarbon-based nature. Together, they literally convey 'vapor oil'—a historically descriptive term highlighting its physical behavior during engine operation.

This word is used exclusively in technical, commercial, and everyday contexts related to vehicles and fueling. It appears on gas station signs (加油站), in news about fuel prices (油价), and in conversations about car maintenance. Unlike broader terms like 燃料 (ránliào, 'fuel'), 汽油 specifically refers to the light, refined fraction used in spark-ignition engines—not diesel, kerosene, or ethanol blends (though in casual speech, people may loosely say 汽油 for 'gas' even at U.S.-style stations).