Facts from the Oil Industry

Types of crude oil

Crude oil quality is measured in terms of density (light to heavy) and sulfur content (sweet to sour).
Density is classified by the American Petroleum Institute (API). API gravity is defined based on density at a temperature of 15.6 °C. The higher the API gravity, the lighter the crude. Light crude generally has an API gravity of 38 degrees or more, and heavy crude an API gravity of 22 degrees or less. Crude with an API gravity between 22 and 38 degrees is generally referred as medium crude. Sweet crude is commonly defined as oil with a sulfur content of less than 0.5%, while sour crude has a sulfur content of greater than 0.5%.

Brent Blend
Brent Blend is a light, sweet North Sea crude with an API gravity of approximately 38 and a sulfur content of approximately 0.4%. Most Brent Blend is refined in Northwestern Europe, but significant volumes are also shipped to the US and Mediterranean countries.
Brent Blend is used for pricing around two-thirds of the crude traded internationally. Rolling price assessments are based on physical Brent-Forties-Oseberg crude oil cargoes loading not less than 10 days ahead and loaded free on board at the named port of shipment (Brent Dated).

Russian Export Blend
Russian Export Blend, the Russian benchmark crude, is a mixture of several crude grades used domestically or sent for export. Russian Export Blend is a medium, sour crude oil with an API gravity of approximately 32 and a sulfur content of approximately 1.2%. Its spot price is reported at Augusta, Italy, and Rotterdam, the Netherlands, which act as the two primary delivery points.

West Texas Intermediate
West Texas Intermediate, the US benchmark crude oil, is a light, sweet crude oil with an API gravity of approximately 40 and a sulfur content of approximately 0.3%. The spot price of West Texas Intermediate is reported at Cushing, Oklahoma.

Impact on refining
The quality of crude oil and other feedstocks dictates the level of processing and conversion necessary to achieve what a refiner sees as an optimal mix of products.
Light, sweet crude is more expensive than heavier, sourer crude because it requires less processing and produces a slate of products with a greater percentage of value-added products, such as gasoline, diesel, and aviation fuel. Heavier, sourer crude typically sells at a discount to lighter, sweeter grades because it produces a greater percentage of lower value-added products with simple distillation and requires additional processing to produce lighter products.

Barrel of crude oil

The standard oil barrel of 42 US gallons is used in the United States as a measure of crude oil and other petroleum products. Elsewhere, oil is commonly measured in cubic metres (m3) or in tonnes (t), with tonnes more often being used by European oil companies.

A barrel of oil is defined as..

  • 42 American (US) gallons
  • 158.9873 liters
  • 34.9726 Imperial (UK) gallons
  • 5.6146 cubic feet
  • 0.15899 cubic metre
  • 3.78541 cubic decimeters (dm3)
  • 0.136 tonne (approx)

The measurement originated in the early Pennsylvania oil fields. In the early 1860s, when oil production began, there was no standard container for oil, so oil and petroleum products were stored and transported in barrels.
International companies listed on American stock exchanges tend to express their oil production volumes in barrels for global reporting purposes, and those listed on European exchanges tend to express their production in tonnes. There can be 6 to 8 barrels of oil in a ton, depending on density. For example.. 256 U.S. gallons of heavy distillate per ton, 272 gallons of crude oil per ton, and 333 gallons of gasoline per ton.

Crude Oil Futures are quoted in dollars and cents per barrel. Minimum Price Fluctuation.. $0.01 (1c/) per barrel ($10 per contract). Maximum Daily Price Fluctuation Futures.. Initial limits of $3.00 per barrel are in place in all but the first two months and rise to $6.00 per barrel if the previous days settlement price in any back month is at the $3.00 limit. In the event of a $7.50 per barrel move in either of the first two contract months, limits on all months become $7.50 per barrel from the limit in place in the direction of the move following a one-hour trading halt.

The abbreviation for a barrel of oil is "bbl". Seems logical, or not?. There are many stories on the Internet that try to explain this abbreviation...not on this site.


The disappearance of one substance into another so that the absorbed substance loses its identifying characteristics, while the absorbing substance retains most of its original physical aspects. Used in refiningto selectively remove specific components from process streams.

Acid treatment
A process in which unfinished petroleum products such as gasoline, kerosene, and lubricating oil stocks are treated with sulfuric acid to improve color, odor, and other properties.

Chemicals added to petroleum products in small amounts to improve quality or add special characteristics.

Adhesion of the molecules of gases or liquids to the surface of solid materials.

Alicyclic hydrocarbons
Cyclic (ringed) hydrocarbons in which the rings are made up only of carbon atoms.

Aliphatic hydrocarbons
Hydrocarbons characterized by open-chain structures.. ethane, butane, butene, acetylene, etc.

A process using sulfuric or hydrofluoric acid as a catalyst to combine olefins (usually butylene) and isobutane to produce a high-octane product known as alkylate.

API gravity
An arbitrary scale expressing the density of petroleum products.

Organic compounds with one or more benzene rings.

The asphalt compounds soluble in carbon disulfide but insoluble in paraffin naphthas.

Atmospheric tower
A distillation unit operated at atmospheric pressure.

An unsaturated, six-carbon ring, basic aromatic compound.

The process of mixing two or more petroleum products with different properties to produce a finished product with desired characteristics.

The removal of hydrocarbons from a process unit, vessel, or line on a scheduled or emergency basis by the use of pressure through special piping and drums provided for this purpose.

Equipment for moving large volumes of gas against low-pressure heads.

Boiling range
The range of temperature (usually at atmospheric pressure) at which the boiling (or distillation) of a hydrocarbon liquid commences, proceeds, and finishes.

Tower bottoms are residue remaining in a distillation unit after the highest boiling-point material to be distilled has been removed. Tank bottoms are the heavy materials that accumulate in the bottom of storage tanks, usually comprised of oil, water, and foreign matter.

Bubble tower
A fractionating (distillation) tower in which the rising vapors pass through layers of condensate, bubbling under caps on a series of plates.

A material that aids or promotes a chemical reaction between other substances but does not react itself. Catalysts increase reaction speeds and can provide control by increasing desirable reactions and decreasingundesirable reactions.

Catalytic cracking
The process of breaking up heavier hydrocarbon molecules into lighter hydrocarbon fractions by use of heat and catalysts.

Caustic wash
A process in which distillate is treated with sodium hydroxide to remove acidic contaminants that contribute to poor odor and stability.

CHD unit
See Hydrodesulfurization.

A high carbon-content residue remaining from the destructive distillation of petroleum residue.

A process for thermally converting and upgrading heavy residual into lighter products and by-product petroleum coke. Coking also is the removal of all lighter distillable hydrocarbons that leaves a residue of carbonin the bottom of units or as buildup or deposits on equipment and catalysts.

The liquid hydrocarbon resulting from cooling vapors.

A heat-transfer device that cools and condenses vapor by removing heat via a cooler medium such as water or lower-temperature hydrocarbon streams.

Condenser reflux
Condensate that is returned to the original unit to assist in giving increased conversion or recovery.

A Heat Exchanger in which hot liquid hydrocarbon is passed through pipes immersed in cool water to lower its temperature.

The breaking up of heavy molecular weight hydrocarbons into lighter hydrocarbon molecules by the application of heat and pressure, with or without the use of catalysts.

Crude assay
A procedure for determining the general distillation and quality characteristics of crude oil.

Crude oil
A naturally occurring mixture of hydrocarbons that usually includes small quantities of sulfur, nitrogen, and oxygen derivatives of hydrocarbons as well as trace metals.

Cycle gas oil
Cracked gas oil returned to a cracking unit.

Process of removing asphaltic materials from reduced crude using liquid propane to dissolve nonasphaltic compounds.

A fractionating column used to remove butane and lighter components from liquid streams.

A fractionating column designed to remove ethane and gases from heavier hydrocarbons.

A reaction in which hydrogen atoms are eliminated from a molecule. Dehydrogenation is used to convert ethane, propane, and butane into olefins (ethylene, propylene, and butenes).

A fractionating column used to remove pentane and lighter fractions from hydrocarbon streams.

A fractionating column for removing propane and lighter components from liquid streams.

Removal of mineral salts (most chlorides, e.g., magnesium chloride and sodium chloride) from crude oil.

A chemical treatment to remove sulfur or sulfur compounds from hydrocarbons.

The removal of wax from petroleum products (usually lubricating oils and distillate fuels) by solvent absorption, chilling, and filtering.

A chemical (C4H11O2N) used to remove H2S from gas streams.

The products of distillation formed by condensing vapors.

Process in which the hydrocarbon stream flows from top to bottom.

Dry gas
Natural gas with so little natural gas liquids that it is nearly all methane with some ethane.

Stock from which material is taken to be fed (charged) into a processing unit.

The process in which a heated oil under pressure is suddenly vaporized in a tower by reducing pressure.

Flash point
Lowest temperature at which a petroleum product will give off sufficient vapor so that the vapor-air mixture above the surface of the liquid will propagate a flame away from the source of ignition.

Lighter petroleum used to fluidize heavier residual so that it can be pumped.

Accumulation of deposits in condensers, exchangers, etc.

One of the portions of fractional distillation having a restricted boiling range.

Fractionating column
Process unit that separates various fractions of petroleum by simple distillation, with the column tapped at various levels to separate and remove fractions their boiling ranges.

Fuel gas
Refinery gas used for heating.

Gas oil
Middle-distillate petroleum fraction with a boiling range of about 350°-750° F, usually includes diesel fuel, kerosene, heating oil, and light fuel oil.

A blend of naphthas and other refinery products with sufficiently high octane and other desirable characteristics to be suitable for use as fuel in internal combustion engines.

A manifold that distributes fluid from a series of smaller pipes or conduits.

As used in the Health Considerations paragraphs of this document, heat refers to thermal burns for contact with hot surfaces, hot liquids and vapors, steam, etc.

High-line or high-pressure gas
High-pressure (100 psi) gas from cracking unit distillate drums that is compressed and combined with low-line gas as gas absorption feedstock.

A process used to convert heavier feedstock into lower-boiling, higher-value products. The process employs high pressure, high temperature, a catalyst, and hydrogen.

A catalytic process in which the principal purpose is to remove sulfur from petroleum fractions in the presence of hydrogen.

A catalytic treating process carried out in the presence of hydrogen to improve the properties of low viscosity-index naphthenic and medium viscosity-index naphthenic oils. It is also applied to paraffin waxesand microcrystalline waxes for the removal of undesirable components. This process consumes hydrogen and is used in lieu of acid treating.

Catalytic reforming of naphtha at elevated temperatures and moderate pressures in the presence of hydrogen to form high-octane BTX aromatics for motor fuel or chemical manufacture. This process results in a netproduction of hydrogen and has rendered thermal reforming somewhat obsolete. It represents the total effect of numerous simultaneous reactions such as cracking, polymerization, dehydrogenation, and isomerization.

The chemical addition of hydrogen to a material in the presence of a catalyst.

Additive used to prevent or retard undesirable changes in the quality of the product, or in the condition of the equipment in which the product is used.

A reaction that catalytically converts straight-chain hydrocarbon molecules into branched-chain molecules of substantially higher octane number. The reaction rearranges the carbon skeleton of a molecule withoutadding or removing anything from the original material.

A hydrocarbon molecule (2,2,4-trimethylpentane) with excellent antiknock characteristics on which the octane number of 100 is based.

Knockout drum
A vessel wherein suspended liquid is separated from gas or vapor.

Lean oil
Absorbent oil fed to absorption towers in which gas is to be stripped. After absorbing the heavy ends from the gas, it becomes fat oil. When the heavy ends are subsequently stripped, the solvent again becomes leanoil.

Low-pressure (5 psi) gas from atmospheric and vacuum distillation recovery systems that is collected in the gas plant for compression to higher pressures.

A general term used for low boiling hydrocarbon fractions that are a major component of gasoline. Aliphatic naphtha refers to those naphthas containing less than 0.1% benzene and with carbon numbers from C3 through C16. Aromatic naphthas have carbon numbers from C6 through C16 & contain significant quantities of aromatic hydrocarbons such as benzene (>0.1%), toluene, and xylene.

Hydrocarbons (cycloalkanes) with the general formula CnH2n, in which the carbon atoms are arranged to form a ring.

Octane number
A number indicating the relative antiknock characteristics of gasoline.

A family of unsaturated hydrocarbons with one carbon-carbon double bond and the general formula CnH2n.

A family of saturated aliphatic hydrocarbons (alkanes) with the general formula CnH2n+2.

The thermal conversion of naphtha and gas oils into high-quality gasoline at high temperatures and pressure in the presence of recirculated hydrocarbon gases.

The process of combining two or more unsaturated organic molecules to form a single (heavier) molecule with the same elements in the same proportions as in the original molecule.

Exchanger used to heat hydrocarbons before they are fed to a unit.

Pyrolysis gasoline
A by-product from the manufacture of ethylene by steam cracking of hydrocarbon fractions such as naphtha or gas oil.

Pyrophoric iron sulfide
A substance typically formed inside tanks and processing units by the corrosive interaction of sulfur compounds in the hydrocarbons and the iron and steel in the equipment. On exposure to air (oxygen) it ignites spontaneously.

Quench oil
Oil injected into a product leaving a cracking or reforming heater to lower the temperature and stop the cracking process.

The product resulting from a solvent extraction process and consisting mainly of those components that are least soluble in the solvents. The product recovered from an extraction process is relatively free of aromatics, naphthenes, and other constituents that adversely affect physical parameters.

The vessel in which chemical reactions take place during a chemical conversion type of process.

An auxiliary unit of a fractionating tower designed to supply additional heat to the lower portion of the tower.

Recycle gas
High hydrogen-content gas returned to a unit for reprocessing.

Reduced crude
A residual product remaining after the removal by distillation of an appreciable quantity of the more volatile components of crude oil.

The portion of the distillate returned to the fractionating column to assist in attaining better separation into desired fractions.

An upgraded naphtha resulting from catalytic or thermal reforming.

The thermal or catalytic conversion of petroleum naphtha into more volatile products of higher octane number. It represents the total effect of numerous simultaneous reactions such as cracking, polymerization, dehydrogenation, and isomerization.

In a catalytic process the reactivation of the catalyst, sometimes done by burning off the coke deposits under carefully controlled conditions of temperature and oxygen content of the regeneration gas stream.

Purification of a gas or liquid by washing it in a tower.

Solvent extraction
The separation of materials of different chemical types and solubilities by selective solvent action.

Sour gas
Natural gas that contains corrosive, sulfur-bearing compounds such as hydrogen sulfide and mercaptans.

A process for separating the gaseous and more volatile liquid hydrocarbons from crude petroleum or gasoline and leaving a stable (less-volatile) liquid so that it can be handled or stored with less change incomposition.

Straight-run gasoline
Gasoline produced by the primary distillation of crude oil. It contains no cracked, polymerized, alkylated, reformed, or visbroken stock.

The removal (by steam-induced vaporization or flash evaporation) of the more volatile components from a cut or fraction.

Sulfuric acid treating
A refining process in which unfinished petroleum products such as gasoline, kerosene, and lubricating oil stocks are treated with sulfuric acid to improve their color, odor, and other characteristics.

Combining sulfur compounds with petroleum lubricants.

Processes that either remove obnoxious sulfur compounds (primarily hydrogen sulfide, mercaptans, and thiophens) from petroleum fractions or streams, or convert them, as in the case of mercaptans, to odorless disulfides to improve odor, color, and oxidation stability.

Switch loading
The loading of a high static-charge retaining hydrocarbon (i.e., diesel fuel) into a tank truck, tank car, or other vessel that has previously contained a low-flash hydrocarbon (gasoline) and may contain a flammablemixture of vapor and air.

Tail gas
The lightest hydrocarbon gas released from a refining process.

Thermal cracking
The breaking up of heavy oil molecules into lighter fractions by the use of high temperature without the aid of catalysts.

Vacuum distillation
The distillation of petroleum under vacuum which reduces the boiling temperature sufficiently to prevent cracking or decomposition of the feedstock.

The gaseous phase of a substance that is a liquid at normal temperature and pressure.

Viscosity breaking is a low-temperature cracking process used to reduce the viscosity or pour point of straight-run residuum.

Wet gas
A gas containing a relatively high proportion of hydrocarbons that are recoverable as liquids.

Other Pages

Part 1..
Introduction to fossil fuels

Part 2..
Oil and Gas exploration

Part 3..
Oil & Gas extraction

Part 4..
Transport & Storage of Crude Oil & Natural Gas

Part 5..
Petroleum Refining Processes

Part 6..
Facts from the Oil Industry

Part 7..
Current Crude Oil prices

Part 8..
Proved Global Oil Reserves

Part 9..
Proved Natural Gas Reserves

Part 10..
The End of the Oil Age?

Explore the World of Piping

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