Cal. Rev. & Tax. Code § 8604

“Fuel” includes any combustible gas or liquid, by whatever name the gas or liquid may be known or sold, of a kind used in an internal combustion engine for the generation of power to propel a motor vehicle on the highways, except fuel that is subject to the tax imposed by Part 2 (commencing with Section 7301) or Part 31 (commencing with Section 60001).

It does not include any combustible gas or liquid specifically manufactured and used for racing motor vehicles at a racetrack.