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Any process that causes one substance to penetrate the inside of another substance. In the case of oil spill clean-up, oil is drawn into porous sorbent materials.

Accute effects
Effects having a sudden onset and lasting a short time

The process that causes one substance to be attracted to and stick to the surface of
another substance, without actually penetrating its surface.

A brown to black residue formed from weathered petroleum products, consisting chiefly of a mixture of hydrocarbons, varies in texture from hard and brittle to plastic.

Aromatic hydrocarbon
Carbon-hydrogen compound characterized by the presence of at least one six-carbon ring structure.

Ballast water
Water taken on board a ship to control trim, list, draught, stability or stresses of a ship.

A unit of volume equal to 42 U.S. gallons or 159 litres at 60 degrees F, often used to measure volume in oil production, transportation and trade.

A naturally occurring clay, which is often a major constituent of drilling muds.

Bilge water
The bilge is the parts of a vessel between the lower-most floorboards and the bottom, where oil-contaminated wastewater - bilge water - drains until further processing. Bilge water is produced when the machinery spaces of a vessel are cleaned.

The adding of microorganisms to the existing native oil-degrading population ( also known as seeding, fertilization, biostimulation or bioremediation).

The breakdown of organic compounds by microorganisms.

Biological agent
Nutrients, enzymes, or microorganisms that increase the rate at which natural biodegradation occurs.

The process of accelerating the rate of natural bio-degradation of hydrocarbons by adding fertilizer to provide nitrogen and phosphorus. Following a spill, there are too few of these chemicals compared with the amount of hydrocarbons. (See also bioaugmentation, biostimulation, fertilization, and seeding).

Also known as nutrient enrichment, the method of adding nutrients such as phosphorus and nitrogen, to a contaminated environment to stimulate the growth of the microorganisms capable of biodegradation. See also bioaugmentation, bioremediation, fertilization, and seeding).

Black oil
A black or very dark brown layer of oil. depending on the quantity spilled oil tends to quickly spread out over the water surface to a thickness of about 1 millimeter. However, from the air, it is impossible to tell how thick a black oil layer is.

Subdivision of sea area for the purpose of licensing to a company or companies for exploration/production right. A block in the UK is approximately 200-250 sq.km.

Uncontrolled flow of of oil or gas from a well which occurs when formation pressure exceeds the pressure applied to it by the column of drilling fluid. Every modern rig has a set of large control valves, known as blowout preventers, to stop the flow of oil, gas and other well fluids if problems occur during drilling.

Containment booms are used to control the spread of oil to reduce the possibility of polluting shorelines and other resources, as well as to concentrate oil in thicker surface layers, making recovery easier.

Bottom (single, double)
See Single hull or Double hull

Bulk carrier
All vessels designed to carry bulk cargos such as grain, fertilizers, ore and oil.

Cargo transfer
When oil is moved from one vessel to another by means of pumping.

Clean ballast water
Ballast water carried in a tank which has, since it was last used to carry oil, been thoroughly cleaned and the residues resulting from the cleaning have been discharged and the tank emptied.

A solid-fuel product containing about 80 per cent of carbon produced by distillation of coal to drive off its volatile constitutents.

Response to oil spills (fighting oil spills).

Combatting vessel
Vessel specifically designed for the purpose of combatting spills of oil and other hazardous substances at sea.

Combination carrier
Means a ship designed to carry either oil or solid cargos in bulk.

Contingency plan
A document that describes a set of procedures and guidelines for containing and cleaning up oil spills.

Convergence line
A line on the water surface where floating objects and oil collect. Convergences are common in the marine environment.

Continental shelf
A geological term that refers to the zone of the sea floor around a continent that extends from the shoreline and where the water depth is much shallower than in the open sea. Typical depths range from 100 to 800 metres compared to 2,000 to 7,000 metres or more for the open ocean.

A process in which molecules are cracked, e.g., the oil-refining process in which heavy oils are broken down into hydrocarbons of lower molecular weight by heat or with a catalyst.

A unit in an oil refinery in which heavy fractions from crude oil are broken down (cracked), using a catalyst, into lighter distillates.

Crude oil (crude oil petroleum)
A fossil fuel formed from plant and animal remains many million of years ago. It comprises organic compounds built up from hydrogen and carbon atoms and is, accordingly, often referred to as hydrocarbons. Crude oil is occasionally found in springs or pools but is usually drilled from wells beneath the earth's surface.

Crude oil tanker
An oil tanker engaged in the trade of carrying crude oil.

Crude oil washing
Crude oil washing (COW) is a system whereby oil tanks on a tanker are cleaned out between voyages not with water, but with crude oil - the cargo itself. The solvent action of the crude oil makes the cleaning process far more effective than when water is used. COW is mandatory on new tankers under the International Convention for the Prevention of Pollution by Ships (MARPOL 73/78).

The fragments of rock dislodged by the bit and brought to the surface in the drilling mud.

Removal of production equipment from depleted oil fields.

Dedicated clean ballast tanks (DBT)
Dedicated clean ballast tanks (CBT) means that specific cargo tanks are dedicated to carry ballast water only.

Development well (also production well)
Well drilled in order to produce oil or gas after an appraisal has proved the reserves to be sufficiently large for exploitation.

Dispersant - Dispersing agent
Chemicals that are used to break down spilled oil in small droplets (see surfactant)

The breaking up of an oil slick into small droplets that are mixed into the water column by breaking waves and other sea surface turbulence.

Water soluble compounds in an oil may dissolve into the surrounding water. This depends on the composition and state of the oil, and occurs most quickly when the oil is finely dispersed in the water column. Components that are most soluble in sea water are the light aromatic hydrocarbons compounds, such as benzene and toluene.

Double bottom • Double sides • Double hull
Single hull is a ship construction term. In tankers with single hulls, oil in the cargo tanks is separated from the seawater only by a bottom and a side plate. Should this plate be damaged as a result of a collision or stranding, the contents of the cargo tanks risks spilling into the sea. An effective way of avoiding the risk is to surround the cargo tanks with a second internal plate which is at a sufficient distance from the external plate (generally 1.5-2 metres). This design, known as a double hull, safeguards cargo tanks from damage and thus reduces the risk of oil pollution. The double hull construction incorporates both double bottoms and double sides. An alternative solution is to have ships with double sides (double hull along the sides of the ship, an added side-shell plating structure fitted within the ship while the bottom of the ship has a single plate, a single bottom. This means that the cargo tanks are separated from the seawater only by a bottom plate. Double bottom, on the other hand, is a ship construction term referring to two separate but continuous and water-tight plating structures along some length and width of a ship's bottom.

Drilling mud, drilling fluid
Specialized fluid made up of a mixture of clays, water (sometimes oil) and chemicals, which is pumped down a well during drilling operations to lubricate the system, remove cuttings and control pressure.

Drilling rig
The complete machinery and structure needed for drilling a well.

Emergency response
The actions taken when an oil spill has occurred.

The formation of a mixture of two liquids, such as oil and water, in which one of the liquids is in the form of fine droplets and is dispersed in the other. Different oils show different tendencies to emulsify. An emulsified mixture of water and oil is commonly called "mousse"; its presence indicates a spill that has been on the water for some time.

The loss of oil from containment when it is pulled under a boom by a strong current.

The physical change by which any substance is converted from a liquid to a vapour or gas.

Exploration well
A collective term for appraisal wells drilled to search for oil and gas.

The method of adding nutrients such as phosphorus and nitrogen to a contaminated environment to stimulate the growth of the microorganisms capable of biodegradation. (See also seeding, biostimulation, bioaugumentation or bioremediation).

Flag State
Country of registry of a sea-going vessel. A sea-going vessel is subject to the maritime regulations in respect of manning scales, safety standards and consular representation abroad of its country of registration.

Controlled burn-off of gas which must be released from an oil producing facility for safety reasons.

Fuel oil
A liquid petroleum product having a flash point above 37,8 degrees C used, e.g., in industrial furnaces, domestic heaters, and ships.

Gelling agent
Gelling agents, also known as solidifiers, are chemicals that react with oil to form rubber-like solids. The gelled oil is removed from the water using nets, suction equipment, or skimmers. gelling agents can be used in calm to moderately rough seas.

See Single hull or Double hull

A large group of organic compounds containing only carbon and hydrogen; common in petroleum products, vegetable oils etc.

Having a tendency to repeal water; hydrophobic materials will not easily absorb water.

Illegal discharge, illicit discharge
Discharge of a pollutant, e.g., oil, in contravention of national and/or international legislation.

The destruction of wastes by burning at high temperatures.

In-situ burning
In-situ burning of oil involves the ignition and controlled combustion of oil. It can be used when oil is spilled on a water body or on land.

Jack-up rig
Mobile offshore drilling platform with retractable legs, on which the platform rests on the seabed when in operation.

Lethal effects
Effects that are fatal (deadly) to the victim.

Liquified Natural Gas, mainly methane, liquified under pressure and low temperature.

Liquified Petroleum Gas. Propane and butane, liquified under pressure or refrigeration.

MARPOL 73/78
The most important convention regulating and preventing marine pollution by ships is the IMO International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 relating thereto (MARPOL 73/78). It covers accidental and operational oil pollution, as well as pollution by chemicals, goods in packaged form, sewage, garbage and air pollution.

MARPOL Special Areas
In Annexes I, II and V of MARPOL 73/78, certain sea areas are defined as "special areas" in
which, for technical reasons relating to their oceanographic and ecological condition and to their sea traffic, the adoption of special mandatory methods for the prevention of sea pollution is required. Under the Convention, these special areas are provided with a higher level of protection than other areas of the sea.

MARPOL Particularly Sensitive Sea Areas, PSSAs
A PSSA is an area that needs special protection through action by IMO because of its significance for recognized ecological or socio-economic or scientific reasons and which may be vulnerable to damage by international maritime activities. The criteria for the identification of particularly sensitive sea areas, and the criteria for the designation of special areas are not mutually exclusive.
In many cases a Particularly Sensitive Sea Area may be identified within a Special Area and vice versa.

Mechanical containment
The most common type of equipment for mechanical containment of oil following a spill is floating barriers, i.e., different types of booms, barriers and skimmers.

Mechanical recovery
Recovery of oil from the water surface by mechanical means, e.g. skimmers and booms.

A thick foamy oil-and-water mixture formed when petroleum products are subjected to mixing with water by the action of waves and wind. Mousse can range in colour from dark brown to nearly red or tan, and typically has a thickened or pudding-like consistency. Incorporation of up to 75 per cent water into the oil will cause the apparent volume of a given quantity of oil to increase by up to four times.

Natural seep
See oil seep.

Non-petroleum oils
Oils that are not derived from petroleum; this group of oils include, e.g., vegetable oils (olive oil, palm oil, etc.) and animal fats (fish oil, etc).

Offshore blowout
Blowout that occurs at an offshore oil or gas platform. See blowout.

Offshore drilling
Drilling for oil and gas from platforms located offshore, on the continental shelf.

Oil, oils
Crude oil and refined products such as motor oils, fuels, lubricants etc. Also vegetable oils, animal fats and other non-petroleum oils.

Oil field
A productive oil or gas formation comprising one or more reservoirs, usually related to the same geological features.

Oil platform
A fixed structure resting on the seabed or piled into it from which development wells are drilled to exploit an oil or gas field.

Oil recovery
See recoverable oil.

Oil seep
Crude oil and natural gas seeps naturally out of fissures in the ocean seabed and eroding sedimentary rock. These seeps are natural springs where liquid and gaseous hydrocarbons leak out of the ground (like springs that ooze oil and gas instead of water).

Oil separation/filtering equipment
Equipment used onboard ships to separate oil from water in bilge water in order to reduce the concentrations of oil in the waters, so that the bilge water can be discharged into the sea in accordance with international standards.

Oil slick
A layer of oil floating on the surface of water. See also slick.

Oil spill
Accidental release of oil into the marine or terrestrial environment.

Oil spill response
Action taken when an oil spill occurs, to mitigate the effects of the spill as much as possible.

Having a strong affinity for oils; oleophilic materials absorb or stick to oils.

Operational discharge
Discharge occurring during the regular operation of a ship.

A chemical reaction that occurs when a substance is combined with oxygen; oxidation may lead to degradation or deterioration of the substance.

Polyaromatic hydrocarbons (PAHs)
Include around a hundred of the petroleum hydrocarbons and are natural constituents of oil. When fossil fuels are burnt, especially on a small scale when combustion is often incomplete, PAH compounds form and escape to the atmosphere or to water. PAHs occur both in gaseous form and bound to particles (soot).

Isolated, roughly circular patches of oil, ranging in size from a few feet across to hundreds of meters in diameter.

Petroleum, petroleum oils
The term petroleum is nowadays used as a common denotation for crude oil (mineral oil) and natural gas, i.e., the hydrocarbons from which various oil and gas products are made. Petroleum, then, is a collective term for hydrocarbons, whether solid, liquid or gaseous.

Platform drainage
Drainage water from an offshore platform machinery space, but does not include any water from processing and production.

Port State
The state (nation) in which is located the port of use of a ship, and which has legal jurisdiction over those ships which enter the port, irrespective of the ship's flag of registry.

Port State Control, PSC
Port State Control is the inspection of foreign ships in national ports to verify that the condition of the ship and its equipment comply with the requirements of international regulations and that the ship is manned and operated in compliance with these rules.

Product carrier
An oil tanker engaged in the trade of carrying oil other than crude oil.

Reception facility
Installation in a port where ships may discharge different types of waste generated onboard.

Recoverable oil (exploration)
The total volume of hydrocarbons that has been or is anticipated to be produced from a well or field.

Recoverable oil (combatting)
Oil in a thick enough layer on the water to be recovered by conventional techniques and equipment. Only black or brown oil, mousse and heavy sheens are generally considered to be thick enough to be effectively recovered by skimmers.

Utility for processing crude oil into various fractions, e.g., fuel oil, gasoline (petrol), etc.

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

Some heavy refined products have densities greater than one and so will sink in fresh or brackish water. However sea water has a density of approximately 1.025 and very few crudes are dense enough or weather sufficiently, so that their residues will sink in the marine environment. Sinking usually occurs due to the adhesion of particles of sediment or organic matter to the oil. Shallow waters are often laden with suspended solids providing favourable conditions for sedimentation. Oil stranded on sandy shorelines often becomes mixed with sand and other sediments. If this mixture is subsequently washed off the beach back into the sea it may then sink. In addition, if the oil catches fire after it has been spilled, the residues that sometimes form can be sufficiently dense to sink.

Segregated ballast tanks (SBT)
Ship's tanks which are completely separated from cargo oil and fuel oil systems and are permanently allocated to the carriage of ballast water.

Segregated ballast
Ballast water introduced to a tank (a segregated ballast tank) which is completely separated from the cargo oil and oil fuel system and which is permanently allocated to the carriage of ballast.

Adding microorganisms to the environment to speed up biodegradation. See also fertilization, biostimulation, bioaugumentation or bioremediation).

Mobile offshore drilling platform which has floats or pontoons submerged to give stability while operating, kept in position by anchors or dynamic positioning.

Sensitive areas
There are a number of factors that influence whether an area is considered sensitive: the use of area by people (fishing, beach); the presence of habitats important to marine life for spawning, feeding or migration and the presence of rare or endangered species.

Sensitivity map
Sensitivity maps identify biological and human resources at risk from an oil spill. They can also outline spill response countermeasures and priorities for protective measures. These maps show shoreline habitats, identify environmentally sensitive biological resources such as fish, birds and associated shore or marine mammals, and show recreational beaches, marina sites or locations of archaeological significance.

Sewage from vessels is defined as drainage and other wastes from any form of toilet and urinal.

A very thin layer of oil (less than 0.0003 mm in thickness) floating on the water surface. Sheen is the commonly-observed form of oil during the later stages of a spill. Depending on thickness, sheens range in colour from dull brown for the thickest sheens to rainbow, grays, silver, and near-transparancy in the case of the thinnest sheens.

Single hull • Single bottom
Single hull
is a ship construction term. In tankers with single hulls, oil in the cargo tanks is separated from the seawater only by a bottom and a side plate. Should this plate be damaged as a result of a collision or stranding, the contents of the cargo tanks risks spilling into the sea. An effective way of avoiding the risk is to surround the cargo tanks with a second internal plate which is at a sufficient distance from the external plate (generally 1.5-2 metres). This design, known as a double hull, safeguards cargo tanks from damage and thus reduces the risk of oil pollution. The double hull construction incorporates both double bottoms and double sides. An alternative solution is to have ships with double sides (double hull along the sides of the ship, an added side-shell plating structure fitted within the ship while the bottom of the ship has a single plate, a single bottom. This means that the cargo tanks are separated from the seawater only by a bottom plate. Double bottom, on the other hand, is a ship construction term referring to two separate but continuous and water-tight plating structures along some length and width of a ship's bottom.

See Sedimentation.

A skimmer is a device for recovering spilled oil from the water's surface. Skimmers may be self-propelled, used from the shore, or operated from vessels.

The common term used to describe a film of oil on the water surface. Most oils tend to spread horizontally into a smooth and slippery surface, called a slick, on top of the water.

Slop tank
A tank specifically designated for the collection of tank drainings, tank washings and other oily mixtures.

The 1974 International Convention for the Safety of Life at Sea contains internationally agreed rules and standards to secure that ships are constructed, equipped and manned in ways that will ensure safety of life at sea.

Substances that take up and hold water or oil. Sorbents that are used in oil spill cleanup are made of oleophilic materials.

Specific gravity
The ratio of the density of a substance to the density of water; substances with a specific gravity greater than one are denser than water and sink. Substances that have a specific gravity less than one are less dense than water and float.

Accidental release of oil or other hazardous substance into the marine or terrestrial environment.

As soon as oil is spilled, it starts to spread out over the sea surface, initially as a single slick. The speed at which this takes place depends to a great extent upon the viscosity of the oil. Slicks quickly spread to cover extensive areas of the sea surface. Spreading is rarely uniform and large variations in the thickness of the oil are typical. After a few hours the slick will begin to break up and, because of winds, wave action and water turbulence, will then form narrow bands or windrows parallel to the wind direction. The rate at which the oil spreads is also determined by the prevailing conditions such as temperature, water currents, tidal streams and wind speeds. The more severe the conditions, the more rapid the spreading and breaking up of the oil.

Waste water (stormwater) flushed into the the general sewer system or into storm drains along roadsides when streets, roofs, handling areas in ports, and other hard surfaces are washed
by rain and snow.

A narrow line of oil, mousse or sheen on the water surface, surrounded on both sides by clean water. Streamers result from the combined effects of wind, currents, and/or natural convergence zones.

Sub-lethal effects
Injuries that affect the health and physical condition of organisms (including eggs and larvae) but do not result in the death of juveniles or adult organisms.

Surface tension
The attractive force exerted upon the surface molecules of a liquid by the molecules beneath the surface. When oil is spilled on water, this tension makes the oil behave as a continuous sheet that is difficult to separate or break up.

A substance that breaks up oil into small droplets.

Surveillance (airborne)
urveillance of sea areas undertaken by aircraft with the purpose to detect discharges (mainly illegal) of hazardous substances from ships.

Means a ship constructed or adapted primarily to carry oil in bulk in its cargo spaces and includes any combination carrier or chemical tanker. Tankers are often characterized according to size:

Supertanker: Tankers of greater size and carrying capacity. Generally considered to be any tanker of over 100,000 deadweight tonnes (dwt).

Handymax tanker: Small-sized oil tankers with less than 50,000 dwt .

Panamax tanker:A maritime standard corresponding to about 65,000 dwt. Refers to a ship with dimensions that allow it to pass through the Panama Canal.

Suezmax tanker:This standard, which represents the limitations of the Suez Canal, has evolved. Before 1967, the Suez Canal could only accommodate tanker ships with a maximum of 80,000 dwt. When the Canal reopened in 1975, the Suezmax capacity went to 150,000 dwt.

Very Large Crude Carriers (VLCC), are tankers with a deadweight of 150,000-300.000 tonnes. They can be ballasted through the Suez Canal.

Ultra Large Crude Carriers (ULCC), are tankers ranging from 300,000 to 550,000 dwt in size. Used for carrying crude oil on long haul routes from the Persian Gulf to Europe, America and East Asia, via the Cape of Good Hope or the Strait of Malacca.

Tank washing
After oil is unloaded, a ship's tanks are cleaned. This process is known as tank washing. Current practice is to use crude oil as the cleaning solution to remove the oil residue from the tank walls. The oil residue and the cleaning solution are then transferred to the load being delivered.

A black or brown hydrocarbon material that ranges in consistency from a heavy liquid to a solid.

Tar balls
Dense, black sticky spheres of hydrocarbons formed from weathered oil.

A facility where ships land to load, transfer or unload their cargo.

Vapour recovery
Collecting and condensing petroleum product vapour formed when oil is being loaded and unloaded at terminals, refineries and petrol stations. The vapours are then condensed to a liquid, thereby significantly reducing air pollution.

Having a resistance to flow; substances that are extremely viscous do not flow easily.

The tendency of a liquid to hold itself together. Viscous liquids do pour freely and have the consistency of syrup or honey.

Volatile organic compounds (VOCs)
A mixture of propane, butane and several other gases given off through the vaporization of crude oil and refined products, such as petrol. VOCs are usually divided into non-methane (nmVOCs) and methane. As soon as petroleum is handled in the open air, vapours escape unless something is done to contain them. These hydrocarbons in gaseous form can be emitted into the atmosphere from platforms (extraction of oil), tankers (transportation of oil), terminals (loading and unloading of oil), filling stations (petrol tanking) refineries (processing of oil), pipelines (leakages of oil), and aircraft ( fuel dumping). Hydrocarbon vapours can be recovered and "recycled" as liquid fuel. They are collected and condensed when petroleum products are being loaded and unloaded at terminals, refineries and petrol stations.

Any of a class of pliable substances of plant, animal, mineral or synthetic origin. Waxes generally consist of long-chain organic compounds. Waxes are included in the residue formed following the refining of crude oil.

Action of the wind, waves and water on a substance, such as oil, that leads to disintegration or deterioration of the substance.

An underwater structure that controls the flow of water. Weir type oil skimmers use a damlike underwater barrier that lets oil flow into the skimmer while holding back the water.

Streaks of oil that line up in the direction of the wind.

  • U.S. Environmental Protection Agency (EPA). Oil Learning Center. Understanding Oil Spills and Oil Spill Response. Glossary of oil spill-related words and terms.
  • NOAA. Open-Water Oil Identification Job Aid for Aerial Observation. Glossary of standard terms used in pollution response.
  • NOAA. Introduction to Coastal Habitats and Biological Resources for Spill Response. Glossary of oil spill terms.
  • Environment Canada. Environmental Emergencies: Oil, Water and Chocolate Mousse. Glossary of oil spill-related words and terms.
  • California, County of Santa Barbara, Energy Division. Glossary of oil and gas words and terms (oil and gas in general, and hydrocarbons as a special section).
  • Mineral Services Management, U.S. Department of the Interior, Gulf of Mexico Region. Glossary of commonly used terms in oil and gas leasing and exploration activities.
  • Statoil, Norway: Glossary of oil industry terms
  • Institute of Petroleum, U.K: Glossary of selected terms used in the oil industry
  • UNEP and OGP: "Environmental management in oil and gas exploration and production". Report by UNEP Industry and Environment (IE) and Oil Industry International Exploration and Production Forum (now International Association of Oil & Gas Producers, OGP). Glossary of oil-related terms (exploration) on pages 55-57.