Petroleum, or 'shí yóu', is a naturally occurring, flammable liquid found beneath the Earth's surface. The word is a compound noun: 石 (shí) means 'stone' or 'rock', and 油 (yóu) means 'oil'. Together, they literally convey 'rock oil'—a direct reference to how petroleum seeps from rock formations and is extracted from underground reservoirs. It’s a key fossil fuel used globally for energy, transportation, plastics, and many industrial products.

In Chinese, 石油 is used in formal, technical, and everyday contexts—from news reports about energy policy to classroom science lessons and environmental discussions. Unlike colloquial terms like 汽油 (qì yóu, gasoline), 石油 refers specifically to crude oil before refinement. It rarely appears in idioms or metaphorical expressions and is almost always used in its literal, scientific sense.