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Abrasive Wear
Wear between two surfaces in relative motion due to particles (three body) or surface roughness (two body).

Acid Number
A measure of the amount of KOH needed to neutralize all or part of the acidity of a petroleum product.

Any material added to a base stock to change its properties, characteristics or performance.

Adhesive Wear
Wear caused by metal-to-metal contact; characterized by local welding and tearing of the surface.

Aniline Point
The lowest temperature at which equal volumes of aniline and hydrocarbon fuel or lubricant base stock are completely miscible. A measure of the aromatic content of a hydrocarbon blend, used to predict the solvency of a base stock or the cetane number of a distillate fuel.

Antifoam Agent
An additive used to suppress the foaming tendency of petroleum products in service. May be a silicone oil to break up surface bubbles or a polymer to decrease the number of small entrained bubbles.

Antistatic Additive
An additive that increases the conductivity of a hydrocarbon fuel to hasten the dissipation of electrostatic charges during high-speed dispensing, thereby reducing the fire/explosion hazard.

Antiwear Agents
Additives or their reaction products, which form thin, tenacious films on highly loaded parts to prevent metal-to-metal contact.

Apparent Viscosity
A measure of the viscosity of a non-Newtonian fluid under specified temperature and shear rate conditions.

Metallic deposits formed in the combustion chamber and other engine parts during high-temperature operation.

Ash (Sulfated)
The ash content of an oil, determined by charring the oil, treating the residue with sulfuric acid, and evaporating to dryness. Expressed as % by mass.

Automatic Transmission Fluid (ATF)
Fluid for automatic, hydraulic transmissions in motor vehicles.



Additive to inhibit bacterial growth in the aqueous component of fluids, preventing foul odors.

Compounds that react with acids to form salts plus water. Alkalis are water-soluble bases, used in petroleum refining to remove acidic impurities. Oil soluble bases are included in lubricating oil additives to neutralize acids formed during the combustion of fuel or oxidation of the lubricant.

Base Number
The amount of acid (perchloric or hydrochloric) needed to neutralize all or part of a lubricant's basicity, expressed as KOH equivalents.

Base Oil Credit
In lubricant cost calculations, the value of the base fluid displaced by the additive package.

Base Stock
The base fluid, usually a refined petroleum fraction or a selected synthetic material, into which additives are blended to produce finished lubricants.

Also called asphalt or tar, bitumen is the brown or black viscous residue from the vacuum distillation of crude petroleum. It also occurs in nature as asphalt "lakes" and "tar sands". It consists of high molecular weight hydrocarbons and minor amounts of sulfur and nitrogen compounds.

Black Oils
Lubricants containing asphaltic materials, which impart extra adhesiveness, that are used for open gears and steel cables.

Passage of unburned fuel and combustion gases past the piston rings of internal combustion engines, resulting in fuel dilution and contamination of the crankcase oil.

Boundary Lubrication
Lubrication between two rubbing surfaces without the development of a full fluid lubricating film. It occurs under high loads and requires the use of antiwear or extreme-pressure (EP) additives to prevent metal-to-metal contact.

Bright Stock
A heavy residual lubricant stock with low pour point, used in finished blends to provide good bearing film strength, prevent scuffing, and reduce oil consumption. Usually identified by its viscosity, SUS at 210°F or cSt at 100°C.

Denting caused by impact of one bearing component against another while stationary.

Brookfield Viscosity
Measure of apparent viscosity of a non-Newtonian fluid as determined by the Brookfield viscometer at a controlled temperature and shear rate.



Eccentric shafts used in most internal combustion engines to open and close valves.

Carbon Residue
Coked material remaining after an oil has been exposed to high temperatures under controlled conditions.

Catalytic Converter
An integral part of vehicle emission control systems since 1975. Oxidizing converters remove hydrocarbons and carbon monoxide (CO) from exhaust gases, while reducing converters control nitrogen oxide (NOx) emissions. Both use noble metal (platinum, palladium or rhodium) catalysts that can be "poisoned" by lead compounds in the fuel or lubricant.

The formation and subsequent collapse of vaporous cavities within a liquid; caused by movement or vibration within the liquid film.

Cavitation Damage
An erosion process in which metal is removed by cavitation.

Cetane Index
A value calculated from the physical properties of a diesel fuel to predict its Cetane Number.

Cetane Number
A measure of the ignition quality of a diesel fuel, as determined in a standard single cylinder test engine, which measures ignition delay compared to primary reference fuels. The higher the Cetane Number, the easier a high-speed, direct-injection engine will start, and the less "white smoking" and "diesel knock" after start-up.

Cetane Number Improver
An additive (usually an organic nitrate) that boosts the Cetane Number of a fuel.

Copper Strip Corrosion
A qualitative measure of the tendency of a petroleum product to corrode pure copper.

Corrosion Inhibitor
Additive that protects lubricated metal surfaces from chemical attack by water or other contaminants.

Corrosive Wear
Wear caused by chemical reaction.

The top of the piston in an internal combustion engine above the fire ring, exposed to direct flame impingement.



A measure of a fluid's ability to separate from water.

Mass per unit volume.

A substance added to a fuel or lubricant to keep engine parts clean. In motor oil formulations, the most commonly used detergents are metallic soaps with a reserve of basicity to neutralize acids formed during combustion.

An additive package that combines a detergent with a dispersant.

Uncontrolled burning of the last portion (end gas) of the air/fuel mixture in the cylinder of a spark-ignition engine. Also known as "knock" or "ping."

Dilution of Engine Oil
Contamination of crankcase oil by unburned fuel, leading to reduced viscosity and flash point. May indicate component wear or fuel system maladjustment.

An additive that helps keep solid contaminants in a crankcase oil in colloidal suspension, preventing sludge and varnish deposits on engine parts. Usually nonmetallic ("ashless"), and used in combination with detergents.

The basic test used to characterize the volatility of a gasoline or distillate fuel.



Elastohydrodynamic Lubrication (EHD)
A lubricant regime characterized by high unit loads and high speeds in rolling elements where the mating parts deform elastically due to the incompressibility of the lubricant film under very high pressure.

Emissions (Mobile Sources)
The combustion of fuel leads to the emission of exhaust gases that may be regarded as pollutants. Water and CO2 are not included in this category but CO, NOx and hydrocarbons are subject to legislative control. All three are emitted by gasoline engines; diesel engines also emit particulates that are controlled.

Emissions (Stationary Sources)
Fuel composition can influence emissions of sulfur oxides and particulates from power stations. Local authorities control the sulfur content of heavy fuel oils used in such applications.

Additive that promotes the formation of a stable mixture, or emulsion, of oil and water.

End Point
Highest vapor temperature recorded during a distillation test of a petroleum stock.

Engine Deposits
Hard or persistent accumulation of sludge, varnish and carbonaceous residues due to blow-by of unburned and partially burned fuel, or the partial breakdown of the crankcase lubricant. Water from the condensation of combustion products, carbon, residues from fuel or lubricating oil additives, dust and metal particles also contribute.

EP Additive (Extreme Pressure Agent)
Lubricant additive that prevents sliding metal surfaces from seizing under extreme pressure conditions.

Wearing away of a surface by an impinging fluid or solid.

Exhaust Gas Recirculation (EGR)
System to reduce automotive emission of nitrogen oxides (NOx). It routes exhaust gases into the carburetor or intake manifold where they dilute the air/fuel mixture and reduce peak combustion temperatures, thereby reducing the tendency for NOx to form.



False Brinelling
Fretting of one bearing component against another; may appear as a dent, but original surface finish is worn away.

Cracking, flaking or spalling of a surface due to stresses beyond the endurance limit of the material.

Magnetic particle analysis.

Flash Point
Minimum temperature at which a fluid will support instantaneous combustion (a flash) but before it will burn continuously (fire point). Flash point is an important indicator of the fire and explosion hazards associated with a petroleum product.

Fluid Friction
Occurs between the molecules of a gas or liquid in motion, and is expressed as shear stress. Unlike solid friction, fluid friction varies with speed and area.

Wear resulting from small amplitude motion between two surfaces; may produce red or black oxide.

Resistance to motion of one object over another. Friction depends on the smoothness of the contacting surfaces, as well as the force with which they are pressed together.

Field of micropits; form of microadhesive wear.

Fuel Ethanol
Ethanol (ethyl alcohol, C2H5OH) with impurities, including water but excluding denaturants.



Gaseous Fuels
Liquefied or compressed hydrocarbon gases (propane, butane or natural gas), which are finding increasing use in motor vehicles as replacements for gasoline and diesel fuel.

A volatile mixture of liquid hydrocarbons, containing small amounts of additives and suitable for use as a fuel in spark-ignition, internal-combustion engines.

Gasoline/Ethanol Blend
A spark-ignition automotive engine fuel containing denatured fuel ethanol in a base gasoline. It may be leaded or unleaded.





Additive that improves the performance of a petroleum product by controlling undesirable chemical reactions, i.e. oxidation inhibitor, rust inhibitor, etc.

Contaminants found in used oils due to dust, dirt, wear particles or oxidation products. Often measured as pentane or benzene insolubles to reflect insoluble character.





Kinematic Viscosity
Measure of a fluid's resistance to flow under gravity at a specific temperature (usually 40°C or 100°C).



Control of friction and wear by the introduction of a friction-reducing film between moving surfaces in contact. May be a fluid, solid or plastic substance.



Multigrade Oil
Engine or gear oil that meets the requirements of more than one SAE viscosity grade classification, and that can be used over a wider temperature range than a single grade oil.



A type of petroleum fluid derived from naphthenic crude oil, containing a high proportion of closed-ring methylene groups.

Neutralization Number
A measure of the acidity or alkalinity of an oil. The number is the mass in milligrams of the amount of acid (HCl) or base (KOH) required to neutralize one gram of oil.

Neutral Oil
The basis of most commonly used automotive and diesel lubricants, they are light overhead cuts from vacuum distillation.

The process whereby nitrogen oxides attack petroleum fluids at high temperatures, often resulting in viscosity increase and deposit formation.



Octane Number
A measure of a fuel's ability to prevent detonation in a spark ignition engine. Measured in a standard single-cylinder, variable-compression-ratio engine by comparison with primary reference fuels. Under mild conditions, the engine measures Research Octane Number (RON); under severe conditions Motor Octane Number (MON). Where the law requires posting of octane numbers on dispensing pumps, the Antiknock Index (AKI) is used. This is the arithmetic average of RON and MON, (R + M)/2. It approximates the Road Octane Number, which is a measure of how an "average" car responds to the fuel.

Occurs when oxygen attacks petroleum fluids. The process is accelerated by heat, light, metal catalysts and the presence of water, acids, or solid contaminants. It leads to increased viscosity and deposit formation.

Oxidation Inhibitor
Substance added in small quantities to a petroleum product to increase its oxidation resistance, thereby lengthening its service or storage life; also called antioxidant.

Oxidation Stability
Resistance of a petroleum product to oxidation and, therefore, a measure of its potential service or storage life.



A type of petroleum fluid derived from paraffinic crude oil and containing a high proportion of straight chain saturated hydrocarbons. Often susceptible to cold flow problems.

Surface cavities; may be related to fatigue, overload or corrosion.

Poise (P)
Measurement unit of a fluid's resistance to flow, i.e., viscosity, defined by the shear stress (in dynes per square centimeter) required to move one layer of fluid along another over a total layer thickness of one centimeter at a velocity of one centimeter per second. This viscosity is independent of fluid density, and directly related to flow resistance.

Polishing (Bore)
Excessive smoothing of the surface finish of the cylinder bore or cylinder liner in an engine to a mirror-like appearance, resulting in depreciation of ring sealing and oil consumption performance.

Pour Point
An indicator of the ability of an oil or distillate fuel to flow at cold operating temperatures. It is the lowest temperature at which the fluid will flow when cooled under prescribed conditions.

Pour Point Depressant
Additive used to lower the pour point or low-temperature fluidity of a petroleum product.

Ignition of the fuel/air mixture in a gasoline engine before the spark plug fires. Often caused by incandescent fuel or lubricant deposits in the combustion chamber, it wastes power and may damage the engine.

The low temperature, low shear stress-shear rate viscosity characteristics of an oil that permit satisfactory flow to and from the engine oil pump and subsequent lubrication of moving components.





Series of processes to convert crude oil and its fractions into finished petroleum products, including thermal cracking, catalytic cracking, polymerization, alkylation, reforming, hydrocracking, hydroforming, hydrogenation, hydrogen treating, Hydrofining, solvent extraction, dewaxing, de-oiling, acid treating, clay filtration and deasphalting.

A process of reclaiming used lubricant oils and restoring them to a condition similar to that of virgin stocks by filtration, clay adsorption or more elaborate methods.

In gear teeth, a form of plastic flow characterized by a rippled appearance on the surface.

Ring Sticking
Freezing of a piston ring in its groove in a piston engine or reciprocating compressor due to heavy deposits in the piston ring zone.

Circular metallic elements that ride in the grooves of a piston and provide compression sealing during combustion. Also used to spread oil for lubrication.

Rolling and Peening
In gear teeth, a form of plastic flow that gives the surface a hammered appearance; metal may be rolled over the teeth tips.

Rust Preventative
Compound for coating metal surfaces with a film that protects against rust. Commonly used to preserve equipment in storage.



Fine abrasive furrows in the direction of sliding.

Abnormal engine wear due to localized welding and fracture. It can be prevented through the use of antiwear, extreme-pressure and friction modifier additives.

Shear Stability Index (SSI)
The measure of a viscosity modifier's contribution to an oil's percentage kinematic viscosity loss, when the oil is subjected to engine operation or special test conditions.

A thick, dark residue, normally of mayonnaise consistency, that accumulates on nonmoving engine interior surfaces. Generally removable by wiping unless baked to a carbonaceous consistency, its formation is associated with insolubles overloading of the lubricant.

Solvent Extraction
Process used to separate reactive components (unsaturated hydrocarbons) from lubricant distillates in order to improve the oil's oxidation stability, viscosity index and additive response.

Solvent Refining
A process for extracting lubricant base stocks from stripped heavy gas oil or other heavy, stripped crude stream using selective solvents such as furfural or phenol.

Severe damage characterized by large pits, cavities and related cracks; related to overload and fatigue.

Stoke (St)
Kinematic measurement of a fluid's resistance to flow defined by the ratio of the fluid's dynamic viscosity to its density.

Synthetic Lubricant
Lubricating fluid made by chemically reacting materials of a specific chemical composition to produce a compound with planned and predictable properties.



Total base number (TBN)
measure of an oil's ability to resist degradation from acids which build up in the oil during use. A high TBN number means that the oil has a high reserve alkalinity and thus a high capability of neutralising potentially harmful acids.





A thin, insoluble, nonwipeable film occurring on interior engine parts. Can cause sticking and malfunction of close-clearance moving parts. Called lacquer in diesel engines.

A measure of an oil's ability to flow. An oil's SAE rating gives an indication of its viscosity and on this basis a 10 grade oil is less viscous than a 20 grade oil. The most common unit of kinematic viscosity is the stoke (St), but as this is a large value, the centistoke (cSt) is more commonly used. Kinematic viscosity is normally measured at 40 and 100 degree C.

Viscosity Index (VI)
Viscosity is affected by temperature and viscosity index (VI) is a measure an oil's ability to maintain its viscosity regardless of temperature. A scale of 0 to 100 is used to indicate the oil's resistance to change in viscosity, and the higher the viscosity index number, the greater the oil's resistance to change in viscosity with temperature.

Viscosity Modifier
Lubricant additive, usually a high molecular weight polymer, that reduces the tendency of an oil's viscosity to change with temperature.