ICE (IntercontinentalExchange)

An electronic marketplace for energy trading and price discovery with several branches worldwide. ICE provides market participants with direct access to energy futures and thousands of over-the-counter commodity products for oil and refined products, natural gas, power and emissions.

Ideal specific gravity

The ratio of the molecular weight of a gas to the molecular weight of air. Molecular weight of air = 28.9644.

Imbalance penalties

Penalties implemented by a pipeline to provide an incentive for shippers to maintain actual receipts and deliveries at nominated and confirmed levels.

Imbalance trading

Process by which shippers can acquire gas from, or sell to, other customers to minimise or avoid cash-out.

Improved (enhanced) recovery

The operation whereby natural gas is recovered using any method other than those that rely primarily on the use of natural reservoir pressure, gas lift, or a pump.

Independent power producer (IPP)

An unregulated power generator that has no franchised retail service territories.


Tying the commodity price of natural gas in a contract to published prices of other commodities or price indices.

Inert gas

A chemically inert gas, resistant to chemical reaction with other substances.

Injected gas

Natural gas placed in underground storage or returned to the producing reservoir to maintain pressure.

Interconnector (the European)

A 238 km pipeline providing a strategic link between the UK and continental Europe, connecting the two gas transmission systems at Bacton, in the UK, and Zeebrugge, in Belgium.

International Energy Agency (IEA)

An organisation that provides energy research for and helps coordinate the energy policy of 28 states within the Organisation for Economic Co-operation and Development (OECD) group of industrialised nations. 

International Gas Union (IGU)

A global industry association of more than 100 member organisations promoting the technical and economic development of the gas sector. Its secretariat is located in Oslo, Norway. The IGU also organises large LNG and gas conferences.

International load line certificate

A certificate that gives details of the minimum freeboard granted to a particular ship and the position of the appropriate load lines to be marked on her sides. This certificate is issued by a government or duly appointed person or organisation such as a classification society.

International Maritime Organisation (IMO)

The United Nations agency with responsibility for the safety and security of shipping and the prevention of marine pollution by ships. 

Interruptible demand

The amount of customer demand that, in accordance with contractual arrangements, can be interrupted by direct control of the system operator, remote tripping, or by action of the customer at the direct request of the system operator.

Interruptible gas

Gas sold to customers with a provision that permits curtailment or cessation of service at the discretion of the supplier; the opposite is firm gas.

Interruptible service

Gas service that is subject to interruption at the option of the pipeline or local distribution company (LDC).

Interstate market

The market for natural gas that is consumed outside the state in which it is produced or is transported by an interstate pipeline.

Interstate Natural Gas Association of America (INGAA)

Trade organisation that advocates regulatory, and legislative and individual positions of importance to the interstate natural gas pipeline industry in the US.

Interstate pipeline

A natural gas pipeline company in the US that is engaged in the transportation of natural gas across state boundaries and is, therefore, subject to FERC jurisdiction.

Intrastate market

The market for natural gas consumed in the same state as it is produced.

Intrastate pipeline

A natural gas pipeline company that is engaged in the transportation of natural gas within the state in which the gas is produced. Subject to regulatory oversight of the applicable state.