Glossary letter O


Refers to sea-based oil exploration and production operations, as in "offshore license" or "offshore drilling".

Offshore Oil

Describes crude oil produced offshore, either in shallow water (depths up to 700 meters) using standard methods, or in deep water, where production requires much more expensive, purpose-developed equipment.

Oil Crisis

An oil shortage that may be real, predicted or caused by speculation. A sudden shortfall in supply versus demand causes oil prices to soar and triggers significant economic consequences on an international scale. There have been three oil crises in recent history. The first occurred in 1973 when Arab countries imposed an oil embargo on Israel’s supporters during the Yom Kippur War. The second arose in 1979 because of the Iran Revolution, followed by the Iran-Iraq War due to the attacks by Iraq. The third, in 2008, was caused by intense speculation.

Oil Derrick (or Mast)


A roughly 30-meter high metal tower that lifts and positions the drill string and inserts it vertically into the ground.

Oil Exploration

All methods used to discover new oil and natural gas deposits.

Oil Pipeline


A pipeline that transports oil and refined petroleum products over long distances on land or underwater.

Oil Platform


A structure that floats or is anchored onto the seabed, used for offshore oil and gas exploration and production.

Oil Sands


Unconventional oil deposits containing extremely viscous, extra-heavy oil. Oil sands are generally found near the surface. Because of this, the conventional oil is degraded as a result of exposure to oxygen and bacteria. The oxidation and degradation caused by bacteria quickly eliminate lighter molecules such as gases and alkanes (paraffins). Oil sands are contained in conventional sand and clay reservoirs and should not be confused with oil shale, from which shale oil is produced by heating the source rock, a process known as retorting.

Oil Shale

Some unconventional deposits of oil are found in microporous, impermeable source rock, known as oil shale, rather than in a standard porous, permeable oil reservoir. Oil shale is found at various depths. Production requires the source rock to be heated to a high temperature, a process called retorting.

Oil Slick

Marée noire

A large film or layer of liquid hydrocarbons floating on water that eventually reaches the shoreline, causing serious environmental damage. It can be caused by an oil tanker sinking, accidental leaks from an oil platform, or deliberate discharge from a ship. A number of safety measures have been introduced to prevent such occurrences.

Oil Supply Chain

The means, including oil terminals and distribution networks, implemented to get petroleum products from refineries to end-users. The core concern is safety. The Seveso Directive, introduced in 1976 and amended in 2003 (Seveso II), sets stringent safety regulations covering measures such as alarms, fire fighting equipment and regular inspections. There are also specific facilities designed to protect the environment, including waste collection containers managed by specialized contractors.

Oil Terminal

Facility that stores petroleum products for refineries, petrochemical plants, ports and manufacturing plants. In addition, it can serve as a strategic local reserve or supply fuel to service stations, businesses and consumers. Also known as a tank farm or oil depot.


Olefin is the old name for alkenes and is still used in the refining industry. Alkenes are hydrocarbons containing at least one carbon-carbon covalent double bond. The simplest alkene is ethylene (CH2= CH2). Alkenes that have been polymerized form the basis of many plastics.


Refers to land-based oil exploration and production operations, as in "onshore seismic data acquisition" or "onshore drilling".

Organic Polymer

Plastic made from renewable resources such as plants, algae or animal matter. Because organic polymers are biodegradable, they could eventually replace oil-based packaging, such as single-use plastic bags. Also called biopolymers.

Organization for Economic Co-operation and Development (OECD)

Founded in 1960, the OECD promotes policies that will improve the economic and social well-being of people around the world. It originally had 20 member countries — 18 European countries along with the United States and Canada. It currently has 34 members, 25 of which are European countries.

Organization of Arab Petroleum Exporting Countries (OAPEC)

Organization created in 1968 by three Arab states — Saudi Arabia, Kuwait and Libya — to separate the production and sale of oil from politics following the oil embargo in response to the Six-Day War. There are currently 11 member countries (Algeria, Bahrain, Egypt, Iraq, Kuwait, Libya, Qatar, Saudi Arabia, Syria, Tunisia and the United Arab Emirates), which represent more than half of the world's oil reserves.

Organization of the Petroleum Exporting Countries (OPEC)

Created in 1960, OPEC currently has 12 members: Algeria, Angola, Ecuador, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, United Arab Emirates and Venezuela. Its mission is “to coordinate and unify the petroleum policies of its Member Countries and ensure the stabilization of oil markets in order to secure an efficient, economic and regular supply of petroleum to consumers, a steady income to producers and a fair return on capital for those investing in the petroleum industry.” OPEC aims to stabilize oil production and prices by allocating a production quota to each member country.

Osmotic Power

Osmotic power involves placing a volume of salt water and a volume of fresh water in adjoining chambers, separated by a semipermeable membrane. The fresh water moves towards the salt water through the membrane, increasing the pressure when the salt water chamber is closed or raising the level when the salt water chamber is open. The increased pressure or rising water level can be used to drive a turbine that generates electricity. Several osmotic power plant prototypes have been built around the world.


A chemical reaction during which an atom loses electrons. For example, the oxidation of iron produces rust (oxidation of elemental iron Fe into Fe3+ ion).

Oxidation-Reduction (Redox) Reaction

Reaction characterized by the transfer of electrons between two reagents (atoms, ions or molecules): the oxidizing agent that captures the electrons and the reducing agent that loses electrons.