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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.

Additive
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.

Ash
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.