OAPEC

The Organisation of Arab Petroleum Exporting Countries. This grouping includes the Arab members of OPEC as well as certain other minor Arab oil producers such as Tunisia. Its ultimate importance is increased by the proportion of long-term reserves controlled by its members.

Obligatory wells

Exploration wells that an operator undertakes to drill in a given area as a condition for being allocated an exploration licence.

Observation well

This is a special well drilled to allow observation of fluid levels, changes in pressure etc. within the reservoir as production proceeds.

Observation/s (tidal)

A series of measurements taken in order to provide the information required for the reduction of sounding, and the data for tidal prediction and investigation.

Oceanographic

Concerning the chemical/physical parameters of the sea (e.g. tides, currents and salinity).

Octane

The saturated hydrocarbon (alkane) with eight carbon atoms in its molecule (C8H 18); the eighth member of the paraffin series -a liquid under normal conditions.

Octane number

A measure of the resistance of a fuel to pre-ignition ("knock") when burned in an internal combustion engine.

Odorant

A substance such as mercaptan that is added to natural gas and natural gas liquids when used as fuel {which are normally odourless) to give them a characteristic smell and thus enable them to be detected.

OECD

Organization of Economic Cooperation and Development

Offshore

The adjective applied to any structure of activity located or carried out at sea as opposed to on land {onshore).

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