Octane has a general formula of C8H18 and is classified as alkanes. The phases of alkane at room temperature vary as the numbers of carbons are increase. Generally, alkane with 4 carbons or less are gas at room temperature. As the carbon number is increased, the phases change (solid - liquid - gas).
In case of octane, it is liquid. But due to changes in temperature, it varies its phases. Sometime it becomes more viscous. To prevent that, oil companies are mixing octane with other gases to maintain the desired phase. It is maintained at liquid state because it is in the mixture of other gases.