The terms light and heavy in reference to crude can be misleading. Rather than referring to weight, they actually refer to density, with “light” crude being less dense than heavy crude. Light crude has a low viscosity and because it has low wax content, it is a liquid at room temperature. These properties make it easy to pump and extract. Light oil constitutes approximately 30% of the world’s petroleum reserves.
Light crude is composed of a high number of paraffins, which are straight and branched chain hydrocarbons that have a high hydrogen to carbon ratio. Essentially, they have two hydrogen atoms for every carbon atom they contain. Because hydrogen weighs roughly 12 times less than carbon, paraffins are lighter and less dense than hydrocarbons with a lower hydrogen to carbon ratio. The best light crudes contain roughly 60% paraffin.
Light crude not only has a high number of paraffins, but the paraffins that is does contain tend to be shorter in length. Currently, gasoline is the most valuable product derived from crude oil. The bulk of “typical” gasoline contains paraffins that are 10 carbon atoms in length. That is, the hydrocarbons in gasoline are mostly made up by linking 10 carbon atoms end to end to create a chain. The chain length range in gasoline is 4 to 12 carbons. Because light crude naturally contains a high number of these short chains, it does not have to be refined to a great extent to produce gasoline.