Oil, from crude to fuels and chemicals

Petroleum - what we often think of as oil - powers a large sector of the world economy.  Crude oil, a naturally-occurring mix of substances produced by ancient life and transformed by time and geological forces, lies trapped beneath soil, rock, and the sea floor.  When captured and refined, the crude oil can be transformed into gasoline and diesel, but also into a wide variety of other fuels and chemicals.

In the U.S., crude oil is typically quantified in a 42-gallon unit known as the barrel.  While this bears some historic tie to actual barrels of oil, crude oil today is seldom packed in actual 42-gallon barrels, more typically being shipped in large seagoing oil tankers or pipelines.

At a refinery, each of the components of the crude oil mix is separated.  Some are converted from heavy, low-valued chemicals into lighter, higher-valued products like gasoline.  Processes like cracking, coking, and alkylation allow the production of more exotic petroleum derivatives.

From 42 gallons of crude oils, refineries can produce about 45 gallons of refined petroleum products. Typically, these might include:

• 19 gallons of gasoline
• 10 gallons of diesel
• 4 gallons of jet fuel
• 2 gallons of liquefied petroleum gases (propane, butane, etc.)
• 1 gallon of other distillates (heating oil)
• 2 gallons of residual fuel oil
• 7 gallons of other products

Most of this increase in total product volume comes as different fractions of the petroleum mix are distilled and transformed; the U.S. Energy Information Administration has described the increased volume after refining as "similar to what happens to popcorn, which gets bigger after it's popped".

Because each source of crude oil contains a different mix of hydrocarbons and other chemicals, the refining process yields different mixes of products for each type of crude. The demand for these products drives oil producers' decisions about where to drill and produce oil.