Petroleum refining

In plain language

Crude oil is a mixture of many different molecules, most of them made from carbon and hydrogen. A refinery heats the crude and separates it into groups, called fractions, by boiling point. The lightest fractions boil off first and become fuels such as petrol, while the heaviest material is left behind as residue. Early refining was simple. In Pittsburgh, Samuel Kier's still began producing kerosene for lamps, and Edwin Drake's 1859 oil strike at Titusville, Pennsylvania, helped start the wider oil industry.

Refiners also learned to break big molecules into smaller ones, a process called cracking. In 1913 William Burton's thermal cracking used heat and pressure to make more petrol from the same crude. In the 1930s Eugene Houdry's catalytic cracking used a catalyst to make high-octane petrol. Today's refineries also make diesel, jet fuel and lubricating oils, and they remove sulphur from fuels. Refining has an environmental cost. EPA reports that sulphur dioxide and nitrogen oxide emissions from refineries are about 75 per cent below pre-Refinery Initiative levels, after a steady decline that began with the first settlements in 2000.

Technical explanation

Distillation separates crude oil into cuts based on boiling point (Schobert, 2020). The residuum, the part that does not distil, can be treated to separate lubricating oils and waxes. Petrol quality is judged by octane number, which describes how readily the fuel knocks in an engine (Schobert, 2020).

Thermal cracking uses heat and pressure. William Burton's process, whose first battery of twelve stills began operating in January 1913 at Standard Oil of Indiana's Whiting refinery, ran as a batch process. Continuous thermal cracking processes were developed in the 1920s (Heitmann, EBSCO, 2021). According to Schobert (2020), catalytic cracking can give gasolines with octane ratings above 90 and raises refinery gasoline output to roughly 45 per cent, although that source gives no baseline. Catalytic reforming changes the shape of molecules rather than cracking them, and can give octane numbers close to 100 (Schobert, 2020). Hydrotreating uses hydrogen to remove sulphur and aromatic compounds.

Early thermal-cracking petrol was discoloured and smelled bad because of sulphur compounds, and it needed sulphuric acid treatment to improve it (Heitmann, EBSCO, 2021). Modern pollution control targets sulphur dioxide and nitrogen oxides. The sources reviewed for this profile give no verified greenhouse gas figures for refining, so climate impact is not assessed here.

What the evidence says

Each statement is typed by the strength of its evidence and linked to the source that supports it.

Limitations and open problems

• Early thermal-cracking petrol was discoloured and smelled bad because of sulphur compounds, and needed sulphuric acid treatment (Heitmann, EBSCO, 2021).
• Burton's thermal cracking ran as a batch process, and continuous processes came later (Heitmann, EBSCO, 2021).
• The roughly 45 per cent gasoline output figure for catalytic cracking has no stated baseline or crude type in its source, so it cannot be compared directly with other yields (Schobert, 2020).
• The EPA page gives the 75 per cent reduction in sulphur dioxide and nitrogen oxide emissions without stating the baseline year, and it covers those two pollutants only (EPA, last updated 2026).
• The sources reviewed do not give verified greenhouse gas figures for refining, so this profile does not assess climate impact.

Possible future uses

Timeline

1. 27 Aug 1859Edwin Drake's well at Titusville, Pennsylvania, reaches 69½ feet and strikes oil. Sources: [2]
2. Jan 1913The first battery of twelve Burton thermal-cracking stills begins operating at Standard Oil of Indiana's Whiting refinery. Sources: [3]
3. 1936A Houdry catalytic cracking plant at Paulsboro, New Jersey, produces over 2,000 barrels per day of high-octane gasoline. Sources: [4]
4. 2000The first of the EPA's refinery settlements is reached, after which refinery sulphur dioxide and nitrogen oxide emissions decline steadily. Sources: [7]
5. 13 Aug 2009The American Chemical Society announces that the Pennsylvania oil industry, including Kier's Pittsburgh still and Drake's well, will be designated a National Historic Chemical Landmark. Sources: [1]

Glossary

Distillation

Separating a liquid mixture into parts by heating it so that each part boils off at a different temperature.

Cracking

Breaking long hydrocarbon molecules into shorter ones, using heat and pressure with or without a catalyst.

Octane number

A measure of how well a petrol resists knocking, or uncontrolled burning, in an engine. Higher numbers mean better resistance.

Residuum

The heavy part of crude oil that does not distil and is left after the lighter fractions have boiled off.

Sources

1. news
   ACS to honor origins of Pennsylvania oil industry in two Chemical Landmark ceremonies
   American Chemical Society (news release, hosted on EurekAlert!), 13 Aug 2009. Accessed 22 Oct 2026.
2. other
   Site History
   Drake Well Museum and Park, 2026. Accessed 22 Oct 2026.
3. other
   Burton Refines Petroleum with Thermal Cracking
   John A. Heitmann. EBSCO Research Starters, 2021. Accessed 22 Oct 2026.
4. other
   Eugene Houdry
   Dinesh Kapur. EBSCO Research Starters, 2020. Accessed 22 Oct 2026.
5. other
   Petroleum refining and processing
   Harold H. Schobert. EBSCO Research Starters, 2020. Accessed 22 Oct 2026.
6. other
   Cracking
   R. C. Lutz. EBSCO Research Starters, 2013. Accessed 22 Oct 2026.
7. government report
   Petroleum Refinery National Case Results
   US Environmental Protection Agency, 20 Oct 2026. Accessed 22 Oct 2026.

Revision history

3 changes since this profile was created.