Octane number – measure of the anti-detonator characteristics and quality of petrol; the aim is for the air-fuel mixture not to ignite before it is ignited under control by the electrical spark of the spark-plug in the engine; the detonator characteristics of the tested petrol are compared to a mixture of n-heptane (which detonates easily) and iso-octane (which does not detonate); when petrol burns satisfactorily in mixture with air and behaves as a mixture of 5% n-heptane and 95% iso-octane, is has octane number 95.
Odorisation – designation/marking of gas intended for consumption; has intensive smell due to blending of chemical matters for the purpose of spotting possible leakage on the device or installation into the atmosphere.
Off-shore – exploration and production of petroleum (oil) and gas from the sea.
Oil distillation – process in which crude oil is separated into specific ingredients by distillation.
Oil equivalent - (OE), (with equal value), unit quantity of petroleum in comparison to quantities of other energy sources of equal energetic value: 1 t of petroleum is equal to (approximately) 11,000 mt of natural gas as well as 1.4 t of pit coal, or to 4.7 t of heating wood where energy is concerned.
Oil/petroleum flow pipeline – a steel pipeline below ground from an oil/petroleum well to an oil/petroleum metering station.
Oil refinery – processing plant for refining crude oil into useful products.
Organic theory – a theory of the genesis of petroleum that is based on the transformation of organic matter from extinct organisms, deposited on the bottom of a sea or lake, into petroleum through the mediation of high temperatures and pressures.
Organic matter (biomass) – biogenic material resulting from biological processes and containing one or more carbon atoms. Kerogen, bitumen, petroleum and gas are organic materials preserved in rocks.
Organic compounds – chemical compounds which contain carbon and hydrogen.
Oxygenates – ethers that contain oxygen and have a high octane number. Oxygenates usually used for production of motor fuels are: methyl tertiary butyl ether (MTBE), tertiary-amyl-ether ether (TAME), ethyl tertiary butyl ether (ETBE) and diisopropyl ether (DIPE).