iso-Octane is a branched hydrocarbon from the alkane group with the chemical formula C8H18. It is the most important of the eighteen octane isomers. Since it is an important component of motor gasoline, it is produced synthetically, but is also found to a small extent in petroleum.

n-Octane is a chain-like hydrocarbon from the alkane group with the chemical formula C₈H₁₈. It is the unbranched representative and of the eighteen octane isomers.

n-Nonane is a chain-line hydrocarbon from the alkane group with the chemical formula C₉H₂₀. It is the unbranched representative of the nonanes.

Isododecane is a branched hydrocarbon from the group of the alkanes and has a chemical formula C₁₂H₂₆. However, it is actually a mixture of different isomers of dodecane, usually one molecule is the main isomer, 2,2,4,6,6-pentamethylheptane. This is also the technically most important one.