Before the widespread invention of the internal combustion engine oil refineries considered gasoline to be a completely useless and highly dangerous byproduct of producing kerosene for lamps.

Why gasoline was left over

Early oil refineries were built chiefly to make kerosene, the relatively steady-burning fuel used in lamps. To get it, refiners heated crude oil and separated the vapors that boiled off at different temperatures. The lighter fractions came off before kerosene; gasoline was among them.

That lightness made gasoline troublesome. It evaporated readily, and its vapor could ignite explosively when mixed with air. In a refinery geared toward lamp fuel, this volatile liquid was a risky surplus with few buyers. Some operators burned it off or disposed of it, including by dumping it into waterways.

The engine changed the value of the light fraction

An internal-combustion engine could turn gasoline’s volatility from a hazard into an advantage. In a spark-ignition engine, fuel mixes with air and is ignited inside a cylinder; the expanding hot gases push the engine’s moving parts. Gasoline vaporizes readily enough to form that combustible mixture, making it useful as a compact fuel for vehicles.

As automobiles spread, refineries had reason to recover and improve the gasoline fraction instead of treating it as waste. The same material that had posed a disposal problem became a product with a growing market. The change was not that gasoline became less volatile, but that engines gave its volatility a controlled job.