O

Octane Number
A measure of the resistance of a fuel to pre-ignition ("knock") when burned in an internal combustion engine. The higher the number, the more anti-knock quality.

Odorant
A substance, such as a mercaptan, that is added to odorless natural gas and natural gas liquids; gives them a characteristic smell and thus enables them to be detected.

Oil
A mixture of liquid hydrocarbons of different molecular weights.

Oil Field
A geographical area under which an oil reservoir lies.

Olefins
Basic chemicals made from oil or natural gas liquids feedstocks; commonly used to manufacture plastics and gasoline. Examples are ethylene and propylene.

OPEC
The Organization of Petroleum Exporting Countries, which are Algeria, Indonesia, Iran, Iraq, Kuwait, Libya, Nigeria, Qatar, Saudi Arabia, United Arab Emirates and Venezuela.

Operating Interest
The legal right to produce oil or gas from a well, accompanied by the responsibilities to pay production costs and assume the risks.

Operator
Term used to describe a company appointed by venture stakeholders to take primary responsibility for day-to-day operations for a specific plant or activity.

Orthoxylene
An aromatic compound used in the manufacture of plasticizers and polyester.

Outer Continental Shelf (OCS)
That portion of a continental land mass that constitutes the slope down to the ocean floor. The outer continental shelves are heavily sedimented, and it is believed they contain a large portion of the earth’s undiscovered oil and gas.