Rock oil, mineral oil, or natural oil, a dark brown or
   greenish inflammable liquid, which, at certain points, exists in the
   upper strata of the earth, from whence it is pumped, or forced by
   pressure of the gas attending it. It consists of a complex mixture of
   various hydrocarbons, largely of the methane series, but may vary much
   in appearance, composition, and properties. It is refined by
   distillation, and the products include kerosene, benzine, gasoline,
   paraffin, etc.