Glossary of Terms


A compound having a pH below 7.0. An acid is used to react with a metallic compound, forming a metal salt which is then reacted with a fatty acid to form a soap type thickener for grease.

Acid Number

Property of a petroleum fluid usually measured by the amount of (KOH) basic chemical needed to neutralize the fluid’s acidity…also called neutralization number.


Anything added to a petroleum or synthetic base fluid to alter its natural properties or performance characteristics.


The force causing two materials, such as a lubricant and a metal, to stick together.

Age Hardening

Increase in consistency (hardening) of a lubricating grease with storage time.

AGMA (American Gear Manufactures Association)

An organization that establishes and promotes standards for gears and lubricants. See separate AGMA viscosity chart.


A class of hydrocarbons with oxygen in their structure. Methyl (methanol), and ethyl (ethanol) and isopropyl (isopropanol) are used in fuels to boost octane and prevent icing.


Any substance having basic properties with a pH above 7.0 is used in grease terminology to describe the hydroxides of alkali metals, including lithium, calcium and sodium.

Aluminum Base Grease

A grease prepared with lubricating fluid thickened with aluminum soap.

Anti-Foam Agent

Two types are used to reduce foaming: 1. A silicone oil to break up large bubbles, or 2. A polymer that reduces the amount of small entrained bubbles.

Anti-Knock Index

See Octane Number

Antioxidant (Oxidation Inhibitor)

An additive usually incorporated in a relatively small proportion, to hinder oxidation of lubricants including greases.

Anti-Wear (AW) Agents

Chemical compounds, or their reaction products, that coat metal surfaces with an aggressive film, preventing metal to metal contact. Sometimes called extreme pressure agents.

API (American Petroleum Institute)

Trade association of producers, refiners, and marketers that conduct research, and gather and disseminate information on all phases of the oil industry.

API Engine Service Categories

Quality levels for gasoline and diesel engine oils, which have been jointly established by the API, ASTM and SAE (see the lubricants information section.)


Hydrocarbons with ring structures. Large quantities not desirable in fuels since high carbon/ hydrogen ratio may result in smoke. Very low aromatic content may lead to lower lubricity in a fuel.


Non-burnable materials; they may be soluble metal compounds (in the case of beneficial additives) and/or abrasive solids (in case of contamination).

Ash (Sulfated)

Weight percentage of ash in lube oils, usually the metallic components of additives. Obtained by charring the oil, treating with sulfuric acid and evaporating to dryness.

ASTM (American Society of Testing & Materials)

An organization devoted to the standardization of the specifications and methods of testing.


Standard unit of measure in the petroleum fraction, usually a lube oil that is used to formulate a finished lubricant. Can be obtained in any number of viscosity classifications.

Base Stock

A primary refined petroleum fraction, usually a lube oil that is used to formulate a finished lubricant. Can be obtained in any number of viscosity classifications.


A naturally occurring earth or clay. When chemically treated, is used as a grease thickener and produces a product known as a “no-melt grease.”

BIA (Boating Industry Association)

A trade association that promotes marine industry standards. Now called the National Marine Manufacturers Association (NMMA).


The separation of oil from grease. A small amount is desirable since the oil lubricates. Storage under pressure and/or high temperatures will increase the bleeding rate.


Seepage of fuel and gases past the piston rings and cylinder wall into the crankcase of an internal combustion engine. Results in crankcase oil dilution, and sludge formation.

Boiling Range

(Distillation) A series of boiling points representing a complex mixture of hydrocarbons in a fuel. Example: Gasoline boiling range is approximately 85°F to 437°F.

Borderline Pumping Temperature

Measured by Mini-Rotary Viscometer (MRV), indicating the capability of an engine’s oil pump to circulate oil from the crankcase throughout the engine.

Boundary Lubrication

When  the  fluid  film separating surfaces is ruptured. This would result in metal-to-metal contact; extreme pressure (EP) additives are then used to reduce wear.

Bright Stock

A highly refined, dewaxed, high viscosity base oil used to improve film strength and anti-scuff capabilities; often blended with lower viscosity base oils in finished lubricants.

BTU (British Thermal Unit)

Defined as the heat required to raise the temperature of one pound of water at its maximum density, 1°F. Also, a measure of potential energy content in fuels.

Calcium Base Grease

A grease made from a lubricating fluid thickened with a calcium soap.

Carbon Residue (Ramsbottom)

A test method using the final 10% of a fuel distillation to determine the amount of carbon residue that fuel contains.


Forming a void due to reduced pressure in a dispensing or pumping system. May be caused by low fluid levels and/or high lubricant viscosity; can result in severe pump wear.

Centipoise (cP)

A measurement of absolute viscosity. One one-hundredth of a pose. Low shear rate oil movement at a controlled temperature.

Centistoke (cSt)

Measurement of a kinematic viscosity. One one-hundredth of a stroke. Gravity is used to produce oil flow through a capillary at a controlled temperature.

Cetane Improver

A chemical that enhances the cetane number (engine method) of diesel fuel. This will not improve the cetane index (calculated method) of the fuel. Usually a nitrate compound.

Cetane Index

A calculated approximation of the cetane number (see below). Two fuel properties are used to calculate: API Gravity and distillation recovery temperatures.

Cetane Number

Defines ignition quality of diesel fuel by a controlled engine test. A higher number indicates better starting capability, the possibility of lower emissions and better economy.


The tendency of a grease or gear lubricant to leave a channel in the mass of product after the bearing or gear is moved.

Cloud Point

A cold temperature test describing the first visual indication of the crystallization of wax in a petroleum product. The temperature at which a cloud or haze first appears.

Cold Crank Simulator (CCS)

A low temperature viscosity testing instrument; used to predict the ability of an oil to produce satisfactory cranking speed in a cold engine for quick starting.

Complex Soap

A soap formed by co-crystalizing two or more compounds, usually improving physical characteristics to a grease, such as higher dropping point or better water resistance.

Compounded Oil

Petroleum oil blended with animal or vegetable fat or oil. Strong attraction to metal and extra lubricity make them particularly suitable in wet steam and worm gear applications.

Consistency (Hardness)

The degree to which a plastic material, such as a lubricating grease, resists deformation under applied force. Usually by N.L.G.I. Grade. See Penetration.

Copper Corrosion

A standard test to determine the corrosiveness of a fuel or lubricant acting on a copper strip over a specified period of time.

Corrosion Inhibitor

An additive for protecting metal surfaces against chemical attack by water or other contaminants. Several types are used depending on the application

Crown (Piston)

That part of the piston which is exposed to the combustion chamber, and therefore, to high temperature and pressure.

Cup Grease

Usually a calcium base grease with a buttery texture, for use in grease cups.

Deicing Agent

An additive to keep water from freezing in fuel tanks or lines and carburetors.


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


An additive that reduces deposits by neutralizing contamination in a fuel or lubricants system.

Diesel, Rudolf

German inventor who developed the compression ignition engine in 1897.


A petroleum additive usually combined with a detergent, that reduces deposits by suspending contamination until it can be freed from the system.


Commonly used term referring to a petroleum fuel produced from crude oil by a combination of heat and reduced pressure.


The process of evaporating a liquid and condensing the vapors to form another liquid. The temperature required to distill a percentage of fuel can indicate performance.

Dropping Point

A test procurement which defines the temperature at which a drop of the lubricating fluid separates from the grease structure. This is not the melting point of the grease.


Used as colorants in fuels and some lubricants for identification purposes.


Ethyl, or grain, alcohol (CH3CH2OH). An “oxygenate” (contains oxygen) used in gasoline to boost octane number and reduce emissions. Produced by fermenting starch from plant matter.

Film Strength

The ability of a film of lubricant to resist rupture due to load, speed and temperature.

Filter Index

Ratio of time required to filter a “dirty” sample versus a “clean” sample. A high filter index (approximately 1.5, or above) indicates a tendency to prematurely plug filters.

Flash Point

The lowest temperature at which vapors above a combustible material will ignite (flash), but not burn, when exposed to a flame.

Form Oil (Concrete)

A lubricant applied to the surfaces of metal or wooden forms to keep hardened concrete from adhering to the forms.

Four Ball EP Test

The four ball extreme pressure (EP) test machine rotates three hardened steel balls, covered with the lubricant being tested, against a fourth steel ball. Load is applied until the balls seize, then weld. Useful as an indication of extreme pressure properties of a lubricant.


A form of wear resulting from oscillating or vibratory motion of limited amplitude resulting in the removal of very finely divided particles from rubbing surfaces which then oxidize. Also called Fretting Corrosion.


A lubricant composed of a lubricating fluid which has been thickened with a soap or other material to a semi-solid or solid consistency.


Oxidation by-products in fuels which may adversely affect filters, injectors and fuel supply systems.


The basic elements of hydrogen and carbon found in petroleum.

Hydrodynamic (Fluid Film) Lubrication

Lubrication state where a continuous fluid film prevents contact between surfaces.

Hydrofinishing (Hydrotreating)

A refining process that uses hydrogen at high pressure and temperature to create saturated molecules, thereby improving stability.


Two lubricating greases show incompatibility when a mixture of the products shows that physical properties or service performance are markedly inferior to those of either grease before mixing.


Additive used to inhibit or control an undesirable side reaction or process which would destroy the petroleum product’s usefulness, i.e., oxidation inhibitor, rust inhibitor, etc.

Inorganic Thickener

See Non-Soap Thickener.


Contaminants found in used oil due to dust, dirt, wear particles and/or oxidation products.

ISO Viscosity Classification System

International Standards Organization (ISO) viscosity grades for industrial lubricants corresponding to kinematic viscosity, in centistokes (cSt) at 40°C.

Lead Additive (Anti-Knock)

Usually tetraethyl lead (TEL) or tetramethyl lead (TML) – banned from gasoline for on-road use since January 1, 1996.

Lithium Base Grease

A grease prepared from a lubricating fluid thickened with a lithium soap.

Manganese Additive (Anti-Knock)

See MMT.

Mechanical Stability

See Shear Stability.


Methyl, or wood, alcohol (CH3OH). Generally used as after-market gas line de-icer and octane booster. Limited to very small concentrations by most automobile manufacturers.

Methylmanganese Tricarbonyl (MMT)

Recently re-permitted for U.S. use in gasoline – usually as an octane improver. MMT tends to leave a rust colored appearance in the combustion chamber.

Motor Octane Number (MON)

A standard comparison of gasoline anti-knock performance to a reference fuel (iso-octane) related to higher engine speeds (e.g. highway speeds) and accelerate (e.g. while passing). See also Octane Number & Research Octane Number.

MTBE (Methyl Tertiary Butyl Ether)

An oxygenate (CH3OC4H9) manufactured from methanol and  used as a gasoline blending stock to improve octane number and reduce emissions.

Multi-Grade Oil

Oil meeting the requirements of more than one viscosity grade – defining both low and high temperature viscosities. For gear and engine oils, the “W” designates “winter” grade.


A range of hydrocarbons commonly known as a solvent.


A type of petroleum fluid derived from naphthenic crude oil. Contains a high proportion of closed ring methylene groups. Generally lower in wax and lower viscosity index.

Neutral Oil

Paraffinic base stocks processed by solvent extraction after vacuum distillation.

Neutralization Number

An indication of the acidity or alkalinity of a lubricant. Expressed as the milligrams of acid or base to neutralize on gram of oil.

NLGI Number

A numerical scale for classifying the consistency range of lubricating greases. See separate NLGI Grade Chart.

Non-Soap Thickener

Any of several specially treated or synthetic materials used as grease thickeners. Certain types are called Inorganic Thickeners. Metallic soaps of long chain fatty acids are excluded from this terminology.

Octane Number

A standard comparison of gasoline anti-knock performance to a reference fuel (iso- octane). Usually expressed as the average of Research and Motor Octane Numbers (R + M/2). Also referred to as Anti-Knock Index (AKI) or pump octane. See also Motor Octane Number and Research Octane Number.


The process whereby oxygen reacts with petroleum fluids, usually leading to viscosity increase and deposit formation. The reaction accelerates at high temperatures, doubling oxidation with each 18°F increase in temperature above 200°F.

Oxidation Stability

The resistance of lubricants to chemical reaction with oxygen. See above.

Oxygenated Compounds

Components, such as alcohols and ethers that contain oxygen. Used to increase octane or reduce emissions in gasoline. See also Ethanol, methanol.


A type of petroleum fluid derived from paraffinic crude oil, thus containing a high proportion of straight chain hydrocarbons. Source for high viscosity index base oils.


A measure of consistency or hardness of a grease, expressed in tenths of a millimeter that a standard cone penetrates a cup of grease. A softer grease exhibits a higher penetration. Consistency may vary when grease is handled or agitated; therefore penetration may be measured before and/or after mechanical working.

Pour Point

The lowest temperature at which a substance will flow under standard cooling conditions.


The ability of a lubricating grease or oil to flow under pressure, usually at low temperatures.

R & O

Rust & oxidation inhibited oil. A term applied to highly refined industrial lubricating oils formulated for long service in circulating systems – usually referred to as Turbine Oils.

Refrigeration Oil

Refrigeration compressor lubricant – free of moisture & having low wax content to minimize wax precipitation in capillary size passages in the circulating system.

Reid Vapor Pressure (RVP)

A method of determining volatility of gasoline when its temperature is raised from 32°F to 100°F. Usually expressed in pounds/square inch (psi).

Research Octane Number (RON)

A standard comparison of gasoline anti-knock performance to a reference fuel (iso-octane) related to lower engine speeds (e.g. idling) and acceleration (e.g. leaving a stop sign). See also Octane Number.


The undistilled remainder of a liquid after distillation is complete. Residue may cause operational problems if it exceeds allowable limits.

Rheopectic Grease

A lubricating grease that increases in consistency (hardens) upon being subjected to shear (e.g. moving through a distribution line or within a moving bearing).

Saybolt Universal Viscosity (SUS)

The flow time in seconds required for 60 ml of oil to flow through a calibrated orifice under carefully controlled temperature conditions.


Abnormal wear occurring due to localized welding and fracture. Scuffing can be reduced through proper cooling, lubricant selection and viscosity grade.

Shear Stability

A measurement of the ability of a lubricant to withstand shearing


Slipping or sliding of one part of a substance relative to an adjacent part. In oils, this may result in rupturing the crystal or molecule structure, resulting in lower viscosity.


An insoluble substance formed due to oil oxidation and/or interaction with water. Sludge can drop out of the oil and create deposits that interfere with proper operation.


The ability of a lubricating grease to flow to the suction of a dispensing system at a rate at least equal to pump delivery capacity.


A specific type of salt formed by the reaction of fatty acid with an alkali.

Society of Automotive Engineers (SAE)

An organization involved in the establishment of many automotive standards, including the viscosity classification of motor oils and gear lubricants.

Sodium Base (SODA) Grease

A grease prepared from a lubricating fluid thickened with sodium soap.

Solid Lubricant

A class of lubricants that reduce friction and wear by allowing shearing action to take place within the structure of the solid. Examples include graphite, & molybdenum disulfide.

Solvent Refined

See Neutral.

Squeeze-Film Lubrication

Lubrication state in which the oil is squeezed between surfaces, thereby increasing the oil pressure and load carrying capability, and reducing wear.


The capability of a petroleum product to resist oxidation.


Compounds of sulfur occur naturally in petroleum products and must be limited by the refining process to control corrosion and emissions.

Synthetic Lube

A lubricating fluid synthesized from petroleum feed stocks.

Synthetic Thickener

See Non-Soap Thickener.

Tackiness Agent

Additive used in certain types of lubricants to increase adhesive properties, improve retention and prevent dripping and splattering.


A descriptive term applied to greases which appear particularly sticky or adhesive.


The property of a grease which is observed when a small separate portion of it is pressed together and then slowly drawn apart. Can be described by the following terms:
  • Brittle – has a tendency to rupture or crumble when compressed.
  • Buttery – Separates in short peaks with no visible fibers.
  • Long Fiber – Shows tendency to stretch or string out into a long bundle of fibers.
  • Short Fiber – Shows short break-off with evidence of fibers.
  • Resilient – Capable of withstanding moderate compression without permanent deformation.
  • Stringy – Shows tendency to stretch or string out into long fine threads, but with no visible evidence of fiber structure.

Thickening Agent

A small, relatively uniform matrix of solids that suspend oil to form grease. May be fibrous, as with metallic soaps or plates of spheres in case of non-soap thickeners.

Timken EP Test (OK Load)

Extreme pressure test where a loaded cylinder rotates against a block. Lubricant is fed to the contact point.

Total Base Number (TBN)

A test to measure the amount of acid a lubricant can neutralize. In engines, sulfur in fuel reacts with oxygen and then moisture to form the acids to be neutralized.

Twelve-Hydroxy Stearate

A grease soap made by reacting a metal with fatty acid in form of hydrogenated castor bean oil. These soaps generally produce quite shear stable greases.

Vapor Lock

A condition which may occur in a gasoline engine, where gasoline vaporizes in the fuel transfer system due to high volatility and interferes with fuel flow, resulting in fuel starvation.


A measurement of the resistance to flow of a liquid at a specific temperature.

Viscosity Index

Relationship of viscosity to temperature of a fluid. High V.I. fluids tend to display less change in viscosity with temperature than low V.I. fluids.

Viscosity Index Improvers

Additive composed of high molecular weight polymers that improve an oil’s viscosity index by limiting viscosity reduction as oil temperature rises.

Water Resistance

The ability of the lubricating grease to withstand the addition of water to the lubricating system without adverse effects.


The removal of materials from surfaces in relative motion. Generally defined as abrasive when particle removal is due to cutting or abrading (often due to contamination) or chemical when removal is by chemical action.

White Oil

Highly refined lube stock used for specialty applications. Often used to refer to food grade oils.


Subjecting lubricating grease to any form of agitation or shearing action.

Zinc (ZDTP)

Commonly used name for zinc dithiophosphate, a wear and oxidation inhibitor additive used in many lubricants.