2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula₃CCH₂CH(CH₃)₂. It is one of several isomers of octane. This particular isomer is the standard 100 point on the octane rating scale. It is an important component of gasoline, frequently used in relatively large proportions to increase the knock resistance of the fuel.