How gasoline is made

Gasoline is a blend of several refinery streams, and the raw distilled part is not good enough for a modern engine.

stations: 6
things upstream: 12
raw sources: 6
steps from the ground: 5

The short version

Gasoline is blended from several refinery streams. Crude oil is distilled, heavy fractions are broken down in a catalytic cracker, and naphtha is reformed to raise its octane rating. These components, plus ethanol and additives, are mixed to the seasonal specification. Straight distilled gasoline alone would knock too much in modern engines.

Wash and distill the crude

Desalted crude oil is heated and fed into a tall tower where it separates into fractions. The light fraction that comes off the top is straight-run gasoline and naphtha.

Goes in
Crude oil
Crack the heavy oil

Heavy gas oil from the bottom of the tower meets a hot powdered catalyst that breaks its long molecules into short ones. This corrects the imbalance between what a barrel of crude yields and how much gasoline drivers want.
Reform the naphtha

Naphtha is heated with a catalyst, which rearranges its molecules into compounds that resist knocking. The process also gives off hydrogen that the refinery uses elsewhere.

Goes in
Naphtha
Remove the sulfur

Each stream is treated with hydrogen to remove sulfur, which would poison emission-control catalysts in cars. The hydrogen sulfide is captured and turned into sulfur.

Goes in
Hydrogen
Blend to specification

Computer-controlled blenders combine the streams and ethanol to meet an octane rating and a seasonal vapor pressure. Summer blends are less volatile, to limit evaporation.

Goes in
Ethanol
Test and dispatch

Samples are tested before the batch leaves the tank. Pipelines, trains and tank trucks carry it to terminals.

End of the lineGasoline Next it goes into car, car engine, motorcycle.

Worth repeating

Tetraethyl lead was once widely added to raise octane, but American gasoline phased it out starting in 1975 because of the health hazard.
The Shukhov cracking process of 1891 was the world's first commercial way to break heavier crude oil components into lighter ones.
About one-third of the crude oil refined at refineries with a fluid catalytic cracker runs through that cracker to make high-octane gasoline and fuel oils.