An oil refinery, also known as a petroleum refinery, is an industrial process plant where crude oil is transformed and refined into various usable petroleum products such as gasoline, diesel fuel, and heating oils. Refineries are an essential part of the petroleum industrys downstream sector. The refining process involves breaking down crude oil into its various components, which are then selectively reconfigured into new products. The process typically involves three basic steps: separation, conversion, and treatment.

Here are the basic steps of the refining process:

• Separation: Crude oil is piped through hot furnaces, and the resulting liquids and vapors are discharged into distillation units. Inside the distillation units, the liquids and vapors separate into petroleum components, called fractions, according to their boiling points. Heavy fractions are on the bottom and light fractions are on the top.
• Conversion: Cracking is a process that breaks down large molecules of heavy oils, while other refinery processes rearrange molecules rather than splitting molecules to add value. These processes ensure that every drop of crude oil in a barrel is converted into a usable product.
• Treatment: Crude oil naturally contains contaminants such as sulfur, nitrogen, and heavy metals, which are undesirable in motor fuels. The treating process, primarily desulfurization, removes these contaminants.

Refineries are complex and expensive industrial facilities that run 24 hours a day, 365 days a year, and require a large number of employees. They can occupy as much land as several hundred football fields. The final products are stored temporarily in large tanks on a tank farm near the refinery, and pipelines, trains, and trucks carry the final products from the storage tanks to locations across the country.