Aggregate Flow Forecast (AFF) is the total shippers nominations for end of day (EoD) UKCS, import and storage withdrawals


Amsterdam Power Exchange, The Anglo-Dutch APX Group is a provider of power and gas exchanges, operating markets in the Netherlands, the United Kingdom and Belgium (Gas: NBP, TTF and Zee, Power: NL and UK)

Balancing period

The period within which the offtake of an amount of natural gas, expressed in units of energy, must be offset by every network user by means of the injection of the same amount of natural gas into the transmission network in accordance with the transportation contract or the network code

Balancing zone

A geographic gas transmission system zone within which gas injections and offtakes must be balanced.


A market condition in which the prices are falling or are expected to fall


The Balgzand Bacton Line (BBL) is an interconnector that flows gas from Balgzand in the Netherlands to Bacton in the UK. BBL came into operations 1 December 2006. Capacity from March 2007 is 42 mcm.


A mixture of methane and CO2 produced by bacterial degradation of organic matter and used as a fuel. (IEA)


Balance of Month, Price average for gas to be delivered on each of the remaining days of the current month, not counting today.


Balance of Month, Price average for gas to be delivered on each of the remaining days of the current month, not counting today.


Balance of Week, Price average from tomorrow and to the first weekend (not defined on Friday-Sunday).

Cascade control

A system which automatically starts up or stops units in a predetermined sequence to meet variations in the energy demands being served. The sequence may be changed periodically to ensure that the running time of each unit is approximately equal.(DECC UK)

Compressed natural gas

A fossil fuel substitute for gasoline (petrol), diesel, or propane/LPG

Congestion management

Management of the capacity portfolio of the transmission system operator with a view to optimal and maximum use of the technical capacity and the timely detection of future congestion and saturation points.

Contracted capacity

Capacity that the transmission system operator has allocated to a network user by means of a transport contract.

Contractual congestion

A situation where the level of firm capacity demand exceeds the technical capacity.


Day Ahead, Traded price for the first working day after today.

Daily Capacity

Maximum quantity of energy that the Operator undertakes to take off, transmit or deliver each day.


The rate at which the storage facility user is entitled to withdraw gas from the storage facility.

Depreciation policy

The company’s policy for depreciating its assets to reflect wear and tear and the passage of time. (DECC UK)


Delivery flow nominations is the total shippers nominations for the National Transmission system (NTS)

Direct line

A natural gas pipeline complementary to the interconnected system

Discount factor

The factor used to convert net annual cash flow to present value, depending on the interest rate and the number of years from present. Calculated by a derivation of the compound interest formula: DF = 1 (1 + r/100)n where r = % interest rate and n = number of years from now. (DECC UK).

Discount rate

The annual percentage figure used in discounted cash flow analyses to discount the future value of costs/savings to give a Net Present Value. (DECC UK)

Discounted cash flow

A cash flow analysis where the time value of cash is taken into account. (DECC UK)

Entry point

Point where the Shipper makes all or part of the gas available to the Operator. An Entry Point is associated with a single Balancing Zone.


End of Day (EoD) shows all physical gas flows entering National Transmission System (MTS) at the end of the day.

Field Capacity

Maximum daily field production.

Final customer

A customer purchasing natural gas for his own use.

Firm capacity

Gas transmission capacity contractually guaranteed as uninterruptible by the transmission system operator.

Firm services

Services offered by the transmission system operator in relation to firm capacity.

Gas day

Lasts from 06:00 am - 06:00 am in most countries.

Gas supply contract

A contract for the supply of natural gas, but does not include a gas derivative.


Percentage ratio of debt to net assets. (DECC UK)

Henry Hub Prices

Represent the price for natural gas in the US Henry Hub system traded on New York Merchandise Exchange (NYMEX).

Horizontally integrated undertaking

An undertaking performing at least one of the functions of production, transmission, distribution, supply or storage of natural gas, and a non-gas activity

Household customer

A customer purchasing natural gas for his own household consumption.

In-duct burner

A burner comprising an arrangement of fuel nozzles located within a duct along which the combustion air (or oxidant) flows. The fuel nozzles may have their separate supply of cooling or stabilising air. This arrangement is commonly used for supplementary firing of additional fuel using the residual oxygen in gas turbine exhaust as oxidant to boost the exhaust gas temperature before it enters the heat recovery boiler. (DECC UK)


Storage entry capacity.

Integrated natural gas undertaking

A vertically or horizontally integrated undertaking.

Interconnected system

A number of systems which are linked with each other.

Interruptible capacity

Gas transmission capacity that may be interrupted by the transmission system operator in accordance with the conditions stipulated in the transport contract.

Interruptible services

Services offered by the transmission system operator in relation to interruptible capacity.


The Langeled pipeline runs from the Sleipner field on the Norwegian continental self to Easington in UK and was ready for use October 2006 (Langeled southern leg). By October 2007 Langeled northern leg from the Ormen Lange field will be linked to the Sleipner platform. Capacity will be 70 mcm/d.


The storage of gas by compression in gas transmission and distribution systems, but not including facilities reserved for transmission system operators carrying out their functions.

Liquefied natural gas (LNG)

Natural gas that has been liquefied by reducing its temperature to -162°C at atmospheric pressure. In this way, the space requirements for storage and transport are reduced by a factor of over 600.

Liquefied Petroleum Gas (LPG)

A mixture of propane, propylene, butane and butylenes. When compressed moderately at normal temperature it becomes a liquid. It is obtain as light ends from fractionation of crude oil. It has a good caloric value; used as cooking fuel; because LPG has no natural odor, a distinctive odorant is added so that it will be noticeable should a leak occur.

Natural gas liquids (NGLs)

The heavier hydrocarbons or ethane (C2H6), propane (C3H8), butane (C4H10), and natural gasolines which are need to separated through the process of absorption, condensation, adsorption, or other methods in gas processing or cycling plants before transportation of natural gas in pipelines. Typically, these liquids consist of propane and heavier hydrocarbons and are commonly referred to as lease condensate, natural gasoline, and liquefied petroleum gas.


National Balance Point is the virtual unified trading point for the GB gas transmission network.

Network user

A customer or a potential customer of a transmission system operator, and transmission system operators themselves in so far as it is necessary for them to carry out their functions in relation to transmission.


The prior reporting by the network user to the transmission system operator of the actual flow that the network user wishes to inject into or withdraw from the system.

Non-household customer

A customer purchasing natural gas which is not for his own household use.


Non-Local Zone gas consumption outside the local distribution zone (LDZ). Consist of power stations and large industries, linked to the high pressure grid (NTS).


The National Transmission System (NTS) is the high-pressure pipeline system on land UK. High-pressure system consisting of terminals, compressor stations, other pipeline systems and offtakes. Designed to operate at pressures up to 85 bar. NTS pipelines transport gas from terminals to NTS offtakes.


On-the-day Commodity Market.


Opening Linepack (OLP) is the actual volume at 06:00 (the beginning of the gas day).

Physical congestion

A situation where the level of demand for actual deliveries exceeds the technical capacity at some point in time.

Primary market

The market of the capacity traded directly by the transmission system operator.


Short term prices. Covers normally Within Day, Day Ahead, BoW (Balance on Week), Weekend and WDNW (Working Days next Week) prices, price contracts expire 2 working day's before the end of the month.


The subsequent reporting of a corrected nomination.

Secondary market

The market of the capacity traded otherwise than on the primary market.

Short-term services

Services offered by the transmission system operator with a duration of less than one year


The volume of gas which a user of a storage facility is entitled to use for the storage of gas.

Spark spread

The theoretical net income of a gas-fired power plant from selling a unit of electricity, having bought the fuel required to produce this unit of electricity. All other costs (operation and maintenance, capital and other financial costs) must be covered from the spark spread. Spark spread = Price_of_electricity - Price_of_gas / Plant_Electric_Efficiency. The term dark spread refers to the similarly defined difference between cash streams (spread) for coal-fired power plants. The clean spread indicators include the price of carbon dioxide emission allowances.


Short range storage - comprises of the LNG storage facilities


Installation providing for the storage of natural gas in summer, when consumption is lower, and releasing natural gas in winter, when the consumption is higher. Storage facilities are depleted oil or gas fields, salt cavern and LNG tanks.

Storage capacity

Any combination of space, injectability and deliverability.


A synthetic gas primarily composed of hydrogen and carbon monoxide produced by a chemical process.

System integrity

Any situation in respect of a transmission network including necessary transmission facilities in which the pressure and the quality of the natural gas remain within the minimum and maximum limits laid down by the transmission system operator, so that the transmission of natural gas is guaranteed from a technical standpoint..

System user

A natural or legal person supplying to, or being supplied by, the system

Transport contract

A contract which the transmission system operator has concluded with a network user with a view to carrying out transmission.


Title Transfer Facility, the virtual trading point for gas in the Netherlands.

Unused capacity

Firm capacity which a network user has acquired under a transport contract but which that user has not nominated by the deadline specified in the contract.

Upstream pipeline network

Any pipeline or network of pipelines operated and/or constructed as part of an oil or gas production project, or used to convey natural gas from one or more such projects to a processing plant or terminal or final coastal landing terminal.


The Vesterled pipeline runs from the Heimdal platform on the Norwegian Continental shelf and to St Fergus in UK.


Working Days Next Week (WDNW) is the average price for gas to be delivered on each of the working days between the first and next weekend or holiday.


Weekend average prices for the non-working days (normally Saturday and Sunday, but also public holidays in connection with the weekend).

Wholesale customer

A natural or legal person other than a transmission system operator or distribution system operator who purchases natural gas for the purpose of resale inside or outside the system where he is established.


Positive net withdrawal from storage is part of supply.

Working gas

The actual volume of gas that is able to get out of storage. In the storage facilities you also need certain volume of cushion gas, which is gas that is needed to keep the pressure high enough during production or storage.