Octane is a hydrocarbon with the chemical formula C8H18. It is a colourless liquid with a characteristic gasoline-like odour. Octane is one of the main components of petrol (gasoline), and its concentration in petrol is directly related to the fuel's octane rating.

The octane rating of a fuel is a measure of its ability to resist knocking, which is a harmful engine condition that can occur when the air-fuel mixture in the engine ignites too early. The higher the octane rating, the more resistant the fuel is to knocking.

Octane is a branched-chain hydrocarbon, which means that its carbon atoms are arranged in a non-linear fashion. This gives octane a higher octane rating than straight-chain hydrocarbons, such as hexane.

Octane is produced by the refining of crude oil. The octane rating of crude oil can be increased by a process called reforming, which involves converting low-octane hydrocarbons into high-octane hydrocarbons.

Octane is also used as a solvent for paints, varnishes, and other coatings.