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Glossary of Oil Field



The pH of an oil, which may or may not influence the behavior of the oil, depending on the exact mechanism of by which the pH is achieved.


Chemicals added to gasoline in very small quantities to improve and maintain gasoline quality. Detergents and corrosion inhibitors are examples of gasoline additives.

Air-Fuel Ratio:

The ratio of air consumed to fuel consumed, by weight, in an internal combustion engine or other fuel-burning apparatus. Has impact on performance and efficiency.


The largest class of hydrocarbons. These include linear and branched chain molecules typically used in the production of fuel.
Anti-dumping Rule A provision of the 1990 Clean Air Act Amendments which restricts conventional gasolines (those not regulated under reformulated gasoline program) from resulting in any higher levels of emissions than their EPA designated baseline fuel.


Typically an alcohol such as ethanol, isopropyl alcohol, or methanol. Added to gasoline in small amounts to eliminate trace levels of water thereby reducing the chance for fuel line freeze up.

Antiknock Index (AKI):

 Measures the ability of a gasoline to resist engine knock/ping. AKI is the average of Research and Motor Octane or (R+M)/2. Also commonly referred to as pump octane.


A compound used to inhibit gum formation from oxidation of gasoline. A fuel stabilizer.

API Gravity:

The standard by which all crude oils are measured. API gravity is used to determine the specific gravity of crude oil and thus its density. Lighter crudes are more valuable because they are more easily refined into gasoline. Crude with an API gravity of 10 is equivalent in density to water.


 High octane blending components that have benzene ring in their molecular structure. Commonly used term for the BTX group (benzene, toluene, xylene). Aromatics are hydrocarbons.


A volume measure equal to 42 U.S. gallons or approximately 160 liters.


Abbreviation for barrel.

Benchmark Crude:

Benchmark crude oils are used as references for pricing oils. There are approximately 161 different benchmark oils, of which the main three are West Texas Intermediate, Brent Crude, and Dubai Crude.


Basic aromatic in the BTX group. Usually of higher value as a chemical feedstock. A known cancer causing agent.


Brake horsepower or British Horsepower. This is a standard measure of power output for engines.


Any diesel fuel that is created through the transesterification of fat. Comes in various mixtures of 100%, 20%, 5%, and 2%.


Any fuel that is derived from biological carbon fixation that has occurred relatively recently.


Methane produced from fermentation. Often produced by farmers via fermentation of animal waste and used to offset fuel costs.


Bitumen is the geological term that refers to the sticky, highly viscous semi-solid hydrocarbon present in most natural petroleum. It is alternatively called pitch, resin, and asphaltum.

Boutique Fuels:

Gasoline unique to certain areas that have more stringent specifications than conventional gasoline but less stringent than RFG.

British Thermal Unit (btu):

One British thermal unit represents the amount of heat required to raise one pound of water one degree Fahrenheit (at sea level).


 A light hydrocarbon used to increase fuel volatility. Butane has a low boiling point and will vaporize quickly.


Alternative to the term Centigrade below that references physicist Anders Celsius who developed the temperature scale, which sets the freezing point of water at 0 and the boiling point at 100.


Temperature scale in which 0 is the point for water freezing and 100 the point at which water boils. Abbreviated with a capital C.

Cloud Point:

Temperature at which wax begins to and form a solid in a fuel.

Clean Air Act Amendments-1990 (CAAA-90):

A series of amendments to the original Clean Air Act which includes requirements for oxygenated fuel programs in CO non-attainment areas and reformulated gasoline programs in certain ozone non-attainment areas.


Carbon monoxide


Carbon dioxide

Complex Model:

 A computer model that measures the effect of various fuel changes. The computer equations are based on test results from various test programs. Refiners are required to use this model to develop their reformulated gasoline.


 A common term used to describe larger volume ingredients in gasoline.

Corrosion Inhibitors:

An additive used to reduce the corrosion properties of gasoline. Rust inhibitor.


The process in refining oil in which larger hydrocarbons are broken down into smaller components.


Mass of a unit of volume. It is often expressed as mg/L.


In an engine, this is the combustion of the fuel after spark occurs. It produces a characteristic metallic sound, or knock.

Deposit Control Additive:

 Performs same functions as detergent plus minimizes deposit buildup in intake manifold, intake ports, and underside of intake valves (dispersant).


Additive used to prevent and/or clean up carburetor and fuel injector deposits.


Obtained by multiplying the API gravity by the aniline point (the temperature at which a chemical called aniline and diesel mix) of a Diesel fuel, divided by 100. It indicates the quality of the fuel.


The process of heating a liquid to the boiling point, then allowing it to condense in order to collect molecules of different sizes.


A hydrocarbon component of gasoline which contributes to gum and lacquer formation in the fuel system and engine.


Direct injection spark ignition.

Distillation Curve:

The reference to plotting a line connecting the percentages of gasoline that evaporate at various temperatures. Distillation curve is used as an important control for fuel standards such as volatility (vaporization).


An ethanol blend typically comprised of 85v% to 75v% denatured ethanol with the remainder of the blend being gasoline or hydrocarbon components present in gasoline.


Energy Independence and Security Act of 2007.


The rubber like compounds used in fuel lines, evaporative canister lines, etc. Also used for other automotive applications such as brake lines and transmission lines.


A liquid mixture of two or more liquid substances that do not dissolve in one another.


U.S. Environmental Protection Agency.

Ethanol (ethyl alcohol, grain alcohol):

Typically fermented from the starch found in grain. An octane enhancer added at a rate of up to 10 percent in gasoline. Will increase octane 2.5 to 3.0 numbers at 10 percent concentration. Ethanol is a fuel oxygenate. Ethanol can also be used up to 85 volume percent as a fuel in FFVs.

Extra-Heavy Crude:

Crude oil with an API gravity of less than 10. The oil sinks in water.


Temperature scale in which 32 is set as the freezing point of water and 212 as the boiling point. Generally only used in the United States. Conversion to Fahrenheit from Celsius: F = 9/5C + 32, where C is the temperature in Celsius.

Flash Point:

The lowest temperature at which a liquid will generate sufficient vapor to ignite.

Flex-Fuel Vehicle (FFV):

A vehicle that is capable of operating on E85 or 100% gasoline or any mixture of the two.

Fluidizer Oils:

Oils typically used with deposit control additives to control deposit formation on intake valves.

Fossil Fuel:

Fuels formed by natural processes such as anaerobic decomposition of dead and buried organisms. Also fuels include coal, petroleum, and natural gas.


A separate identifiable part of crude oil. Gasoline and kerosene are two different fractions of crude.

Fuel Oil:

The heavy distillates of the oil refining process. Generally used for power stations and in large ship boilers. Contains a high degree of contaminant and produce a great deal of pollution.


In the United States the term gasohol refers to gasoline which contains 10 percent ethanol. This term was used in the late 1970s and early 1980s but has been replaced with the term E10.

Global Warming:

The continuing rise in the average temperature of Earth’s atmosphere and oceans.

Green Diesel:

Diesel fuel derived for renewable resources, but which is produced for a standard fractionation rather than transesterification.

Greenhouse Effect:

The process by which thermal radiation from a planetary surface is absorbed by at the spirit gases and we radiated in all directions.

Greenhouse Gas:

The gas in the atmosphere that absorbs any bits radiation with them a thermal in for reader range. The primary greenhouse gases in the Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone.



Heavy Crude:

Heavy crude oil has an API gravity of less than 20. The largest deposits of heavy crude are found in Canada and Venezuela.

Hydraulic Fracturing (Fracking):

The process used to recover oil that is trapped in sedimentary rocks. Generally consists of drilling followed by the injection of air or water, which may or may not have chemicals mixed in.


An organic compound composed of hydrogen and carbon that makes up the majority of petroleum and which is refined to make fuels.


Hydrogen is the smallest of all atoms. Two hydrogen atoms combined together constitute molecular hydrogen, which can be burned as fuel or used in fuel cells.


The organic matter found in sedimentary rock that contains a mixture of organic chemicals and hydrocarbons and so would form. The solid hydrocarbon part is referred to as bitumen.



Lead (tetraethyl lead):

An organometallic octane enhancer. One gram of lead compound increases the octane of one gallon of gasoline about six numbers. Lead is not permitted in U.S. gasoline (except for certain racing and aviation uses).

Light end Hydrocarbons:

Term used to denote hydrocarbons from crude distillation that are low density (lighter weight than gasoline) and have low boiling temperatures. Butanes are the most common light end hydrocarbon used in gasoline.

Metal Deactivator:

Gasoline additive used to neutralize the effect of copper compounds found in gasoline.


The simplest of all hydrocarbons. It consists of a single carbon with four attached hydrogen and is a gas at room temperature.






Volatile, colorless product of petroleum distillation. Used primarily as paint solvent and cleaning fluid.


 Non-methane organic gases.


 Oxides of Nitrogen.


Crude petroleum and other hydrocarbons in liquid form.

Oil Shale:

Oil shale refers to a type of crude oil that is trapped in sedimentary rock.

Oil Tanker:

Ships used for transporting petroleum across water. Oil tankers can be double-hulled or single-hulled. Oil tankers, the variety of sizes ranging from a those that can safely carry tens of thousands of barrels of oil to those that can carry over two million barrels of oil.


General term for a gasoline’s ability to resist engine knock.

Octane Enhancer:

 Common term designating components that are added to gasoline to increase octane and reduce engine knock. Examples are toluene and ethanol.

Octane Number Requirement (ONR):

The octane level required to provide knock-free operation in a given engine.

Octane Requirement Increase (ORI): 

The increase in octane requirement that results from the build up of combustion chamber deposits.


A gasoline component resulting from several refining processes. Examples are ethylene, propylene, butylene. Olefins often contribute to the formation of gum and deposits in engines and the induction system.


In the petroleum industry a term used to denote octane components containing hydrogen, carbon, and oxygen in their molecular structure. Includes alcohols such as ethanol and ethers such as MTBE.

Oxygenated Gasoline:

Gasoline containing an oxygenate suc as ethanol. Provides chemical enleanment of the A/F charge thereby improving combustion and reducing tailpipe emissions of CO.


Ozone (O3) is formed when oxygen (O2) and other compounds react in sunlight. In the upper atmosphere, ozone protects the earth from the sun’s ultraviolet rays. Though beneficial in the upper atmosphere, at ground level, ozone is a respiratory irritant and considered a pollutant.


The Organization of Petroleum Exporting Countries is an intergovernmental organization of 12 nations that export oil. The countries that make up OPEC are: Algeria, Angola, Ecuador, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, the United Arab Emirates, and Venezuela. OPEC is headquartered in Vienna.

Peak Oil:

On a global scale, this term refers to the point at which extraction of petroleum is at its maximum and after which production of oil can only diminish. Peak oil can also be applied to individual wells and is the point at which maximum oil extraction for that well occurs.


Naturally occurring crude oil consisting of a complex mix of hydrocarbons of various molecular weights and other liquid organic compounds as well as inorganic compounds.

Petroleum Reserve:

A commercially recoverable deposit of oil. Subdivided into proven, unproven, and strategic reserves. A new category was created into 2007 termed resources.


Pipelines are used to transport a number of substances including natural gas, fuels, hydrogen, water, and petroleum.

Pour Poin:

Lowest temperature at which oil will flow freely.

Proven Reserve:

A petroleum reserve in which there is a 90% certainty that the petroleum can be recovered.

Pump Octane:

A term used to describe the octane as posted on the retail gasoline dispenser as (R+M)/2.


 Particulate matter


 Parts per million.

Predictive Model:

 Similar to EPA's Complex Model and used to regulate reformulated gasoline sold in California.

Reformulated Gasoline (RFG):

Gasolines which have had their composition and/or characteristics altered to reduce vehicular emissions of pollutants. Specifically, those gasolines which meet the RFG requirements of the 1990 Clean Air Act Amendments.


Renewable Fuels Standard

Reduced Crude Oil:

Crude oil that has undergone at least one distillation to separate some of the lighter hydrocarbons. Reducing crude lowers its API gravity.

Reducing Agent:

Anything, such as iron or the sulfide ion that will give up electrons. This is the opposite of an oxidizing agent.


The process of separating crude oil into useful components including gasoline, diesel fuel, jet fuel, fuel oil, and other products.


Heavy fuel oils produced from the non-volatile fractional distillation process. Heavy oils that are leftovers after refining.

Research Octane:

The octane as tested in a single cylinder octane test engine operated under less severe operating conditions. Research Octane Number affects low to medium speed knock and engine run-on. Research Octane is represented by the designation R in the (R+M)/2 equation and is the higher of the two numbers.

Sour Crude:

Sour crude has a sulfur content of greater than 0.5% by weight.

Specific Gravity:

Weight of a particle, substance or chemical solution in relation to an equal volume of water at 15C.

Specific Heat:

The quantity of heat required to raise the temperature of a unit weight of a substance by 1 degree.


To make something resistant to change. Organic material can be stabilized by bacteria and will not give off obnoxious odors.


Occurs in blended fuels where the denser fuels settle to the bottom and lighter fuels rise to the top.


An element that is present in crude oil and natural gas as an impurity. Responsible for acid rain.

Sweet Crude:

Sweet crude has a sulfur content of less than 0.5% by weight.


An aromatic compound used to increase octane. One of the more common hydrocarbons purchased for use in increasing octane. Basic aromatic in the BTX group.


 As defined in the 1990 Clean Air Act Amendments, toxics include benzene, 1,3 butadiene, formaldehyde, acetaldehyde, and polycyclic organic matter.


The degree of how poisonous a substance is.

Unproven Reserve:

Geologically equivalent to proven reserves, their unproven status rests on technical, regulatory, or political issues. Unproven reserves fall into two categories: probable and possible. A probable reserve has a 50% chance for petroleum recovery and is termed in the industry P50. A possible reserve, also called a P10 reserve, has a 10% chance of recovery.

Vapor Liquid Ratio:

A measurement of the ratio of vapor to liquid at a given temperature used to help determine a gasoline's tendency to contribute to vapor lock in an automotive fuel system.

Vapor Pressure (VP):

A method of determining vapor pressure of gasoline and other petroleum products. Widely used in thpetroleum industry as an indicator of the volatility (vaporizatiocharacteristics) of gasoline.


Term used to describe a gasoline’s tendency to change from liquid to vapor.

Volume Percent (v%):

 A percentage measurement based solely on volume without regard to differences in weight or density. For instance, a set of four blocks of identical size would each comprise 25 v% of the total volume. (Typically used to measure the concentration of alcohols and ethers in gasoline).

Weight Percent (w%):

A percentage measurement based on weight. For instance a set of four blocks of equal size are each 25v% of the total volume. However, if block A, B, and C each weighed 1 pound and block D weighed 3 pounds, then block D would comprise 50 weight percent of the total weight while only comprising 25 volume % of the total volume. (Typically used to measure the oxygen content of gasoline).

Xylene (w%):

An aromatic compound which is a minor component of gasoline. Highly valued as a chemical feedstock (a hydrocarbon). Xylene is highly photochemically reactive and a major contributor to smog formation. Basic aromatic in the BTX group.