Accommodation Platform/Rig
An offshore platform, or semi-submersible rig, built or adapted to provide living quarters for drilling and production personnel.

Acreage
Land leased for oil and gas exploration and development; usually descriptive of more than one lease.

Additive
A term used generally to indicate special chemicals that may be added to products to improve their characteristics.

Air Drilling
A rotary drilling technique in which compressed air is used instead of fluids to circulate, or bring to the surface, bits of rock and other cuttings from the drill bit.

Air Injection
An enhanced recovery technique in which air is injected into the petroleum formation to increase reservoir pressure.

Air Lift
A production technique in which an air balance beam pumping unit is used to lift oil to the surface.

Alkylation
A refining process for converting light, gaseous olefins into high-octane gasoline components (the reverse of cracking).

Alloy 
A composition of two or more metals.

Annulus 
The space between the drill string and the earthen wall of the well bore, or between the production tubing and the casing.

API Gravity
The universally accepted scale adopted by the American Petroleum Institute (API) for expressing the density of liquid petroleum products. The higher the API gravity, the lighter the oil.

Appraisal Drilling
Drilling carried out following the discovery of a new field to determine the physical extent, amount of reserves and likely production rate of the field.

Appraisal Well
A well drilled as part of an appraisal drilling program.

ARDS
The refiner's shorthand for "atmospheric residual desulfurization," a refining process that removes sulfur from oils.

Aromatics
Class of hydrocarbons that have at least one benzene ring as part of their structure. Generally describes benzene and benzene derivatives.  These products are used as components of unleaded gasolines and as feedstocks for petrochemicals such as cyclohexane and paraxylene, both of which are used in end products like nylons and polyesters.

Artificial Drives
Techniques for producing oil after depletion or in lieu of natural drives; includes waterflooding, natural gas reinjection, inert gas injection, flue gas injection and in-situ combustion.

Artificial Lift
Any of the techniques, other than natural drives, for bringing oil to the surface.

Associated Gas
Natural gas found in association with oil, either dissolved in the oil or as a cap of free gas above the oil.

Associated Liquids
Liquid hydrocarbons found in association with natural gas.

Aviation Gasoline
High-performance petroleum fuels made specifically for piston engine, propeller- driven airplanes.