The following definitions reflect those used by the International Energy Agency (IEA); definitions used by other organisations and publications may vary.


operation and maintenance


open-cycle gas turbine


oxidative coupling of methane


official development assistance


outward direct investment


original equipment manufacturer


open-hearth furnace


Online Information System, an OECD/IEA system for submitting official documents for OECD and IEA committees, standing groups and working parties


other major economies


Oil Market Report (IEA publication)


organic Rankine cycle


ocean thermal energy conversion

observed decline rate

the production decline rate of an oil or gas field after all measures have been taken to maximise production. It is the aggregation of all the production increases and declines of new and mature oil or gas fields in a particular region.

ocean power

energy available for recovery through different types of technologies that exploit the following phenomena: tidal rise and fall (barrages), tidal/ocean currents, waves, temperature gradients, and salinity gradients.


as defined by the IEA, includes crude oil, condensates, natural gas liquids, refinery feedstocks and additives, other hydrocarbons (including emulsified oils, synthetic crude oil, mineral oils extracted from bituminous minerals such as oil shale, bituminous sand and oils from CTL and GTL) and petroleum products (refinery gas, ethane, LPG, aviation gasoline, motor gasoline, jet fuels, kerosene, gas/diesel oil, heavy fuel oil, naphtha, white spirit, lubricants, bitumen, paraffin waxes and petroleum coke).

oil burden

nominal oil expenditures (demand multiplied by the crude price) divided by nominal GDP. This is a proxy of how much any given economy spends on its oil needs in a given year. Typically, the global oil burden hovers around 2% of GDP – excepting during oil price shocks, e.g. in 2008. In other words, the oil burden is one leading indicator of potential economic trouble ahead.


instruments that convey the rights, but not the obligation to engage in a future transaction on an underlying security or in a future contract.

other energy sector

IEA use of this term covers the use of energy by transformation industries and the energy losses in converting primary energy into a form that can be used in the final consuming sectors. It includes losses by gas works, petroleum refineries, coal and gas transformation and liquefaction. It also includes energy used in coal mines, in oil and gas extraction and in electricity and heat

other renewables

as the term is used by the IEA, include geothermal, solar, wind, tide/wave/ocean energy for electricity generation. The direct use of geothermal and solar heat is also included in this category.