But as it flows from a well, crude oil itself is a commodity with very few direct uses. Virtually all crude is processed in a refinery to turn it into useful products like gasoline, jet fuel, home heating oil, and industrial fuel oil. In the early years of the industry, a refinery was little more than a still where the crude was boiled and then the different products were condensed out at various temperatures. The skills required were not all that different from making moonshine, which is why whiskey makers went into oil refining in the nineteenth century. Today, a refinery is often a large, complex, sophisticated, and expensive manufacturing facility.
Crude oil is a mixture of petroleum liquids and gases in various combinations.
Each of these compounds has some value, but only as they are isolated in the refining process. So, the first step in refining is to separate the crude into constituent parts. Some streams can be sold as they are. Others are put through further processes to obtain higher-value products. In simple refineries, these processes are primarily from the removal of unwanted impurities and to make minor changes in chemical properties.