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Refining Crude Oil

What is a refinery?

Petroleum refineries convert crude oil and other liquids into many petroleum products that people use every day. Most refineries focus on producing transportation fuels. On average, U.S. refineries produce about 19 gallons of motor gasoline, 12 gallons of ultra-low sulfur distillate fuel, most of which is sold as diesel fuel, and 4 gallons of jet fuel from a 42 gallon barrel of crude oil. More than a dozen other petroleum products are also produced in refineries. Petroleum refineries also produce liquids that are used by the petrochemical industry to make a variety of chemicals and plastics.

A photo of the Pascagoula Refinery in Mississippi
A night photo of the Pascagoula Refinery, Mississippi

Source: Stock photography (copyrighted)

Refineries operate 24/7

A refinery runs 24 hours a day, 365 days a year and requires a large number of employees. A refinery can occupy as much land as several hundred football fields.

Last updated: June 16, 2016

How crude oil is refined into petroleum products

Petroleum refineries change crude oil into petroleum products that are used as fuels for transportation, heating, paving roads, and generating electricity. Petroleum products are also used as feedstocks for making chemicals.

Refining breaks crude oil down into its various components, which are then selectively reconfigured into new products. Petroleum refineries are complex and expensive industrial facilities. All refineries have three basic steps:

Diagram of a refinery process flow. Adapted from Chevron.

Note: LPG is liquid petroleum gas.
Source: Adapted from Chevron


Modern separation involves piping crude oil through hot furnaces. 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 weight and boiling point. Heavy fractions are on the bottom and light fractions are on the top.

The lightest fractions, including gasoline and liquid petroleum gas (LPG), vaporize and rise to the top of the distillation tower, where they condense back to liquids.

Medium weight liquids, including kerosene and diesel oil distillates, stay in the middle of the distillation tower.

Heavier liquids, called gas oils, separate lower down in the distillation tower, while the heaviest fractions with the highest boiling points settle at the bottom of the tower.

Fluid catalytic cracking distillation unit
Richmond Refinery, Fluid Catalytic Cracking Distillation Column.

Source: Chevron (copyrighted).

Refining workers overlooking a refinery
Caltex, Star Petroleum Refinery, Refining workers overlook refinery

Source: Chevron (copyrighted).


After distillation, heavy, lower-value distillation fractions can be processed further into lighter, higher-value products such as gasoline. This is where fractions from the distillation units are transformed into streams (intermediate components) that eventually become finished products.

The most widely used conversion method is called cracking because it uses heat and pressure to crack heavy hydrocarbon molecules into lighter ones. A cracking unit consists of one or more tall, thick-walled, rocket-shaped reactors and a network of furnaces, heat exchangers, and other vessels.

Cracking is not the only form of crude oil conversion. Other refinery processes rearrange molecules to add value rather than splitting molecules.

Alkylation, for example, makes gasoline components by combining some of the gaseous byproducts of cracking. The process, which essentially is cracking in reverse, takes place in a series of large, horizontal vessels and tall, skinny towers.

Reforming uses heat, moderate pressure, and catalysts to turn naphtha, a light, relatively low-value fraction, into high-octane gasoline components.


The finishing touches occur during the final treatment. To make gasoline, refinery technicians carefully combine a variety of streams from the processing units. Octane level, vapor pressure ratings, and other special considerations determine the gasoline blend.


Both incoming crude oil and the outgoing final products need to be stored. These liquids are stored in large tanks on a tank farm near the refinery. Pipelines then carry the final products from the tank farm to other tanks across the country.

Last reviewed: December 15, 2015

Refineries process crude oil into many different petroleum products. The physical characteristics of crude oil affect how the crude oil is processed to produce the products with the highest value.

Not all crude oil is the same

The physical characteristics of crude oils can be different. In simple terms, crude oils are classified by density and sulfur content. Less dense (lighter) crudes generally have a higher share of light hydrocarbons from which high-value products such as gasoline, diesel fuel, and jet fuel can be recovered with simple distillation. The denser (heavier) crude oils produce a greater share of lower-value products with simple distillation and require additional and more expensive processing to produce higher-value products. Some crude oils also have a high sulfur content, which is an undesirable characteristic in both processing and product quality.

Refineries use more than just crude oil

In addition to crude oil, refineries and blending facilities use and add other oils and liquids to produce finished products that are eventually sold to consumers. These other oils and liquids include liquids that condense in natural gas wells (called lease condensates); natural gas plant liquids from natural gas processing; liquefied gases from the refinery itself; and unfinished oils that are produced by partial refining of crude oil, such as naphthas and lighter oils, kerosene and light gas oils, heavy gas oils, and residuum. Residuum is a residue from crude oil that remains after distilling off all but the heaviest components.

Blending facilities add ethanol and various blending components to produce the finished motor gasoline that is sold for use. Blenders also add biodiesel to petroleum diesel fuel to make a fuel that is sold as biodiesel.

Refining output is larger than input

The total volume of products produced (output) by refineries is greater than the volume of crude oil that is processed (input) by the refinery. This is a result of the products having a lower density than the crude oil that is processed. The resulting increase in the volume of products produced is called processing gain. The total U.S. processing gain was about 6.7% in 2014. In 2014, an average of about 44.81 gallons of refined products was produced for every 42-gallon barrel of oil input into U.S. refineries.

Gasoline accounts for the largest share of total petroleum products produced each year in U.S. refineries.

Bar chart showing U.S. Refiner and blender net production of refined petroleum products, 2013. Finished motor gasoline 48%, Distillate fuel oil 25%, kerosene-type jet fuel 8%, petroleum coke 5%, still gas 4%, residential fuel oil 2%, liqified refinery gases 2%, asphalt and road oil 2%, petrochemical feedstocks 2%, propane 2%, Ohter products 1%
Click to enlarge »

Petroleum products produced from
one 42-gallon barrel of oil input
to U.S. refineries, 2014

Product Gallons
Finished motor gasoline 18.86
Distillate fuel oil 12.52
Kerosene-type jet fuel 3.99
Petroleum coke 2.27
Still gas 1.81
Liquefied refinery gases 1.72
Residual fuel oil 1.23
Asphalt and road oil 0.84
Naptha for feedstocks 0.55
Lubricants 0.42
Other oils for feedstocks 0.29
Miscellaneous products 0.21
Special napthas 0.13
Kerosene 0.04
Finished aviation gasoline 0.04
Waxes 0.004
Total 44.81
Processing gain 2.81

Source: U.S. Energy Information Administration, Petroleum Supply Annual (April 2015)

Note: Calculated as: Refinery yield X 42 = number of gallons of product.

More data »

Last updated: December 10, 2015

Top 10 U.S. refineries* operable capacity

(As of January 1, 2016)





Barrels per calendar day
1 Motiva Enterprises LLC Motiva Enterprises LLC Texas Port Arthur 603,000
2 ExxonMobil Corp. ExxonMobil Refining & Supply Co. Texas Baytown 560,500
3 Marathon Petroleum Corp. Marathon Petroleum Co. LLC Louisiana Garyville 539,000
4 ExxonMobil Corp. ExxonMobil Refining & Supply Co. Louisiana Baton Rouge 502,500
5 Marathon Petroleum Corp. Marathon Petroleum Corp. Texas Galveston Bay 459,000
6 PDV America Inc. Citgo Petroleum Corp. Louisiana Lake Charles 427,800
7 BP PLC BP Products North America Inc. Indiana Whiting 413,500
8 ExxonMobil Corp. ExxonMobil Refining & Supply Co. Texas Beaumont 344,600
9 WRB Refining LP WRB Refining LP Illinois Wood River 336,000
10 Carlyle Group Philadelphia Energy Solutions Pennsylvania Philadelphia 335,000

*Only refineries with Atmospheric Crude Oil Distillation Capacity
Source: Refinery Capacity Report  

See full list of refineries

Last updated: July 10, 2015