2C - best estimate

2D - two dimensional

2P - proven and probable

ACQ - Annual contract quarterly

Appraisal well - Well drilled after the discovery of oil or gas to establish the limits of the reservoir, the productivity of wells in it and the properties of the oil or gas. See also development well

Barrel - (bbl: barrel; mmbbls: million barrels) a unit of measure for oil and petroleum products equal to 42 US gallons or 35 imperial gallons

Bbtud - Billion British thermal units per day

Block - Subdivision of sea area for the purpose of licensing to a company or companies for exploration/production rights. A UK block is 1/30 of a quadrant and is approximately 200-250 sq. km (a quadrant is one degree by one degree.)

Blow-out - Accidental escape of oil or gas from a well during the drilling stage

BOP - Blow out preventer - a high pressure valve fitted to the top of the casing to prevent blow-outs

Boepd - Barrels of oil equivalent per day

Bopd - Barrels of oil per day

bcf - billion cubic feet

Compressor - An engine used to increase the pressure of natural gas so that it will flow more quickly through a pipeline

Condensate - Liquid hydrocarbons separated and recovered from a condensate gas reservoir

Decommissioning - Removal of production equipment and facilities from depleted oil fields

Development well - A well drilled within the proved area of an oil or gas reservoir to the depth of a stratigraphic horizon known to be productive

Directional drilling - Also known as deviated drilling; technique used in production drilling whereby wells are drilled at an angle from a central point so that a number of development wells can be drilled from a single drilling facility

Downhole - A term used to describe tools, equipment, and instruments used in the wellbore, or conditions or techniques applying to the wellbore

Downstream - Refining of crude oil and the marketing and distribution of oil products that occur after refining, as opposed to upstream

Downtime - The time during which offshore operations cannot be continued owing to adverse weather conditions, mechanical or other factors

Drill-bit - The cutting head attached to the drill-pipe

Drilling muds or fluid - Fluid, containing barytes, which is pumped through the drill-string to the bottom of the well, whence it rises to the surface through the space between drill-string and bore-hole wall. It acts as a lubricant and is used to control flow

Dry hole - Any exploratory or development well that does not find commercial quantities of hydrocarbons

E&P - Exploration and production; the "upstream" sector of the oil and gas industry

EOR - Enhanced oil recovery

Equity - Share or interest in an oil or gas licence or field

Exploratory well - A hole drilled: a) to find oil or gas in an area previously considered unproductive; b) to find a new reservoir in a known field, i.e., one previously producing oil and gas from another reservoir, or c) to extend the limit of a known oil or gas reservoir

Farm in - Where a company joins a joint venture in return for paying disproportionately for future joint venture operations

Field - An area consisting of a single reservoir or multiple reservoirs all grouped on, or related to, the same individual geological structural feature or stratigraphic condition. The field name refers to the surface area, although it may refer to both the surface and the underground productive formations

Floater - An offshore drilling platform without a fixed base, usually held in position by anchor chains

FPSO - Floating production storage and offloading vessel

GSA - Gas sales agreement

GSPA - Gas sales and purchase agreement

HSEQ - Health, safety, environment and quality

HSFO - High sulphur fuel oil

IFRS - International financial reporting standards

Integrated - When applied to an oil company, it indicates a firm that operates in both the upstream and downstream sectors (from exploration through to refining and marketing)

Jacket - Supporting structure for an offshore platform

Jack-up - Mobile offshore drilling platform with retractable legs, on which the platform rests on the seabed when operational

Joint venture - Oil and gas companies generally participate projects through their equity share in a joint venture; the relationship between the companies is governed by a joint venture agreement

Kboepd - Thousand barrels of oil equivalent per day

Lease - A legal document conveying the right to drill for oil and gas, or the tract of land on which a lease has been obtained where the producing wells and production equipment may be located

Licence - An exploration licence permits only geological and geophysical surveying and the drilling of shallow wells; a production licence confers exclusive rights on the licensee to search and bore for and get petroleum

Log - The results of a survey which gathers information about the subsurface formations. Logs typically consist of several curves on a long grid that describe properties within the wellbore or surrounding formations that can be interpreted to provide information about the location of oil, gas, and water. Also called well logs

M&A - Mergers and acquisitions

Mmbbls - Million barrels

Mmboe - Million barrels of oil equivalent

MMBtu - Million British thermal units per day

Mmcf - Million cubic feet

Mmcfd - Million cubic feet per day

Mmscfd - Million standard cubic feet per day

Midstream - A term sometimes used to refer to those industry activities that fall between exploration and production (upstream) and refining and marketing (downstream). The term is most often applied to pipeline transportation of crude oil and natural gas

NCS - Norwegian Continental Shelf

NUI - Normally unmanned installation

OPEC - Organisation of petroleum exporting countries, founded in 1960

Operator - One member of a joint venture is appointed operator and has the responsibility of carrying out operations on behalf of the joint venture

P&A - Plugging and abandonment - a depleted well or dry hole that has been (typically) filled with cement with all surface equipment removed

Plateau level - The level of peak production reached by an oil or gas field

Platform - A fixed structure resting on the seabed or piled into it from which development wells are drilled, using directional drilling, to exploit an oil or gas field

PSC - Production sharing contract

Reservoir - A subsurface, porous, permeable rock formation in which oil and gas are found

Seismic - Data that is acquired by reflecting sound from underground strata and is processed to yield a picture of the sub-surface geology of an area

Semi-submersible - Mobile offshore drilling platform with floats or pontoons submerged to give stability while operating, kept in position by anchors or dynamic positioning

Spud - To commence drilling operations

Tbtu - Trillion British thermal units

Topsides - The top part of a platform positioned on the jacket

USV - Un-crewed surface vessel

UKCS - United Kingdom Continental Shelf

Upstream - Upstream covers the exploration, production and transport prior to refining

Wellhead - The equipment at the surface of a well-used to control the pressure and flow of fluids; the point at which the hydrocarbons and water exit the ground or seabed

Wildcat - Speculative exploration well drilled in search of a new oil or gas accumulation