Tail gas

The exhaust gas from any processing unit that is at a low pressure and is usually vented, treated for contaminant removal or combusted.

Take-or-pay (TOP) clause

Contract clause in a sales and purchase agreement (SPA) requiring a minimum quantity of natural gas to be paid for, whether or not delivery is accepted by the purchaser.


Trans-Alaska Pipeline System, the line from Prudhoe Bay, on the North Slope, to the terminal port of Valdez, on the south coast of Alaska.

Tariff gas

Additional natural gas sold to a customer if the total amount of natural gas needed exceeds their original estimate.

tcf (trillion cubic feet)

Volume measurement of natural gas approximately equivalent to one Quad. See Btu, bcf, and mcf


A unit of heating value equal to 100,000 Btu, in common use in the UK; about 56 therms are derived by setting fire to a barrel of crude oil; one therm has around the same heat content as 100 cf of natural gas.

Third-party access (TPA)

Obliges companies operating gas-transmission or -distribution networks to offer terms for the carriage of gas on their systems by other gas distribution companies or particular customers, subject to capacity availability. See Open access

Throughput (pipeline)

The volume of gas flowing (or transported) through a pipeline.

Throughput (processing)

Average amount of raw material that is processed in a given period by a facility, such as a natural gas processing plant, a crude oil refinery or a petrochemicals facility.

Time charter

A form of charter party issued when an LNG vessel is chartered for an agreed period of time. A time charter party is the contract between owner and charterer, and identifies the salient characteristics of the ship and the obligations of the shipowner; specifically the shipowner provides a ship capable of the specified performance and operates the ship according to that performance standard set by the charterer. The charterer pays the owner for the hire of the vessel at an agreed rate.

Tolling agreement

An agreement whereby one party owns (and bears the risks on) the inputs to and outputs from a process, as well as the rights to a portion of the process capacity (the tollee). Another party agrees to operate the process or facility and charges a tolling fee per unit of input that is transformed, or per unit of capacity to which rights are granted (the toller). Under an LNG liquefaction tolling agreement, one company sends a volume of feed gas to a liquefaction facility, wherein the gas is liquefied in return for a pre-established tolling charge.

Tonne mile

A measurement used in the economics of transportation to designate 1 tonne being moved 1 mile; useful to the shipper because it includes the distance to move a commodity in the calculation.

Ton, long (LT)

A long ton is 2,240 pounds. Typically used as the unit measure for sulphur sales.

Ton, short (ST)

A short ton is 2,000 pounds.


A shipping term referring to the total number of tonnes registered or carried or the ship’s carrying capacity.

Tonne, metric

A metric tonne equals 1,000 kilograms or 2,204.6 pounds. The capacity of an LNG baseload plant is typically expressed in tonnes and the unit capital costs for producing LNG are expressed as $/tonne.


Gas merchant who purchases natural gas from a producer, supplier or another trader and resells it to a pipeline, utility or end-user, usually taking title and assisting in arranging transportation. See marketer

Train (liquefaction)

An independent unit for gas liquefaction. An LNG plant may comprise one or more trains.

Transfer pricing

A transfer price is the amount of money that one unit of an organisation charges for goods and services to another unit of an organisation. Perhaps the most important aspect in this area is the Arm’s Length Principle regularly challenged by fiscal authorities, a common principle in International Accounting Standards to see that a transfer price has been calculated and agreed according to normal, fair, equitable, business principles.


The transport of large quantities of natural gas at high pressures, often through national or regional transmission systems.

Transmission company

Company that obtains the major portion of its operating revenues from the operation of a natural gas transmission system and/or from mainline sales to industrial customers.

Transmission line

Pipeline transporting natural gas from principal supply areas to distribution centres, large-volume customers or other transmission lines.


The movement of natural gas for third parties through pipeline facilities for a fee.

Transportation contract

Contract setting forth the terms and conditions applicable to natural gas or electricity transportation services.


Pipeline company that transports natural gas for a shipper.

Transport-or-pay contract

A contract between a natural gas producer and a pipeline company that requires the pipeline company to pay for a set amount of natural gas whether or not the buyer takes delivery of the full amount.

Treating/treatment plant

Facility that treats raw natural gas to remove undesirable impurities such as carbon dioxide, hydrogen sulphide and water vapour.


A period of brisk activity at a plant or receiving terminal when processing units, or portions of them, are shut down either for scheduled maintenance or for the installation of new equipment and systems.

Turnback of capacity

A situation that occurs when shipper contracts expire, without renewal or re-contracting. Shippers turn back all or part of their firm contracted capacity to the pipeline company.