The apparent delivery of gas in the opposite direction to the normal physical flow of gas. This could be done with a physical delivery of gas back to its original point of departure, but is more usually achieved by non-delivery of a contracted cargo or swap arrangement. 


Arranging for alternate supplies of gas in the event the primary source fails to be delivered. 


A market where the price for delivery in a month in the near future is higher than for months further ahead. The opposite of backwardation is Contango. 


1) the requirement imposed by both electricity grids and gas suppliers that supply and demand be equal over a certain time period; 2) the practice by shippers of offsetting (balancing) their gas deliveries from a pipeline with injections of gas supplies into the pipeline on a regular basis. 


Heavy substances loaded by a vessel to improve stability, trimming, sea-keeping and to increase immersion at the propeller. Seawater ballast is commonly loaded in most vessels in ballast tanks, positioned in compartments right at the bottom and in some cases on the sides, called wing tanks. On a tanker, ballast is seawater that is taken into the cargo tanks to submerge the vessel to a proper trim. 

Ballast tank

Compartments at the bottom of a ship or on the sides that are filled with liquids for stability and to make the ship seaworthy. Any shipboard tank or compartment on a tanker normally used for carrying salt-water ballast. When these compartments or tanks are not connected with the cargo system, they are called segregated ballast tanks or systems. 

Bare-boat charter

A charter in which the bare ship is chartered without crew. For a stipulated sum, the charterer takes over the vessel for a stated period of time with a minimum of restrictions. The charterer appoints the master and the crew and pays all running expenses. 

Barrel (b, bl, or bbl)

A volumetric unit of measure for crude oil and petroleum products equivalent to 42 US gallons or 158.978 litres.

Barrel of oil equivalent (boe)

The oil equivalence of natural gas is normally based on the amount of heat released when the gas is burned as compared with burning a barrel of oil. For typical natural gas, burning 6,000 standard cubic feet liberates about the same amount of heat as burning one barrel of an average crude. 

Barrels a day (b/d, bpd, or bbl/d)

A unit of measurement used in the industry for the production rates of oilfields, pipelines and transportation. Gas is sometimes measured in terms of barrels of oil equivalent a day (boe/d) 

Barrels per calendar day (b/cd)

Total throughput divided by number of calendar days. The total divided by actual number of days in operation, or stream days, gives the stream-day rate. This equals or exceeds the calendar-day-rate. Calendar day rates are usually averaged over a long period of time. A calendar day rate multiplied by 365 gives the average annual rate. 

Base conditions

The base temperature and pressure established in a gas measurement contract to which all gas volumes are commonly referred. 

Base gas

The volume of gas that is required in a gas storage structure to maintain enough  pressure to ensure working gas is recoverable. This gas is not available for withdrawal unless field pressure can be maintained in another way such as by replacing it with immiscible injectant. Base gas can be up to half the total stored gas in structures such as depleted fields or aquifers, but less elsewhere. Also known as Cushion gas. 

Baseload (LNG)

A baseload LNG plant is one capable of sustained liquefaction or regasification, often on a large scale. 

Baseload (power)

1) commonly used to describe the amount of power a utility needs to produce constantly around the clock to meet minimum consumer demand; 2) the amount of power a plant or utility is capable of producing constantly. 

Base pressure

Standard unit of pressure used in determining gas volume. Volumes are measured at operating pressures and then corrected to base-pressure volume. Base pressure is normally defined in any gas measurement contract. The standard value for natural gas in the US is 14.73 pounds per square inch absolute (psia), though there are some state-to-state variations. 

Base temperature

An arbitrary reference temperature to which measurements of a volume of gas are referred. The standard value for natural gas in the US is 60°F. 


Acronym for billion cubic feet. Used to measure the volume of large quantities of natural gas. 

Beach gas

Natural gas transported from the ocean to processing terminals on the coast, usually from pipelines. Most commonly used in the UK. 

Beach price

Price applying to natural gas at landfall. 


The width of a ship; also called breadth. 

Best bid

In the context of bids for firm transportation capacity to be released, the highest bid that qualifies under the specified criteria. 


The purchase price suggested by those in a market to purchase a commodity from suppliers. 

Bid-Ask Spread

The market-making differential between buyers and sellers of a commodity. Narrow spreads are a sign of greater market liquidity. 

Bill of lading (B/L)

A legal document by which the master of a ship acknowledges having received in good order and condition (or the reverse) certain specified goods consigned to him by a shipper. Having done so, he must deliver them in similar condition (unless the perils of the sea, fire or enemies prevent him) to the consignees of the shippers at the destination on their paying him the stipulated freight rate. A bill of lading specifies the name of the master, the port and destination of the ship, the goods, the consignee, and the rate of freight. It is signed by the master of the ship and the contract supplier. 


The subdivision of a nation’s exploration and production acreage. Blocks are generally defined in terms of latitude and longitude, at one-degree intervals. Companies may be granted licences to explore, develop or produce hydrocarbons from them. 


The depressuring of a reservoir through production of gas. This can occur with either gas or oil reservoirs at any stage in their lifecycle. 


An uncontrolled flow of natural gas, oil, or water from a well caused by the release of pressure from a reservoir; may be the result of the failure of the containment system. 

Boatswain (Bosun)

On an LNG vessel, effectively a foreman, who directly supervises maintenance operations. 


A closed vessel in which a liquid is heated, or heated and evaporated. Boilers are often classified as steam or hot water, low pressure or high pressure, capable of burning one fuel or a number of fuels. 

Boil-off gas/vapour

Usually refers to the gases produced during storage of volatile liquefied gases, such as LNG. Although LNG is stored at -163°C, just below its boiling point, boil off of small amounts of gas still occurs. This gas may be flared, or used as a fuel at an LNG plant or on LNG tankers, where it can be used to drive turbines. 

Booster station

An installation built at intervals of up to around 100km along a pipeline, which uses compressors to increase the pressure of gas or liquid in the pipe. This maintains consistent flow along the pipe and sufficient pressure at the offtake end. When gas turbines are used to provide compressor power, the station can use some of the gas moving through the line as fuel. Also known as a Compressor station. 

Border price

The price at which gas is traded at the border between countries. The value will be influenced by factors such as customs charges.  

Bottled gas

Liquefied petroleum gas (LPG) stored in a liquid state in steel containers at moderate pressure and ambient temperatures, often for residential or light commercial use. It is usually comprised of Butane or Propane. 

Bow thrusters

Propeller at the lower sea-covered part of the bow of the ship that turns at right angles to the fore-and-aft line and provides transverse thrust to aid manoeuvring. 

Break bulk

To commence discharge of cargo. 


Loosely used to refer to the navigating section of the vessel where the wheelhouse and chart room are located. It lies amidships, aft or very rarely fore over the main deck of a ship. 

British thermal unit (Btu)

An energy unit; the quantity of heat necessary to raise the temperature of one pound-mass of water one degree Fahrenheit from 58.5°F to 59.5°F under a standard pressure of 30 inches of mercury at 32°F. The following conversions would apply to gas that contains exactly 1,000 Btu/cubic foot (cf) – approximately true for most gas delivered in the US 

1 cf = 1,000 Btu 

1 therm = 100 cf = 100,000 Btu 

1,000 cf = 1 mmBtu 

1 bcf = 1 trillion Btu 

1 tcf = 1 quad = 1 quadrillion Btu 


Gas merchant who charges a fee for matching sellers to buyers and who may help arrange gas transportation, but does not take title to the gas. 

Bubble point

The temperature and pressure at which a liquid first begins to vaporise to gas. 

Bulk cargo

Any liquid or solid cargo loaded on to a vessel without packaging, such as LNG or oil. 


Name given to any vertical partition that separates compartments or spaces on a ship. 


A floating object employed as an aid to mariners to mark the navigable limits of channels, their fairways, sunken dangers, isolated rocks, telegraph cables, and so forth. Also used as reference points for navigation. 

Burner tip

The end point at which natural gas is consumed as a fuel. 


A colourless, highly flammable gas that is easily liquefied under pressure for storage and transportation. The term refers to either of two isomeric flammable gaseous alkanes, normal butane (n-butane) and isobutane (i-butane). It has various uses, including as a fuel in Bottled gas. 

Buy/Sell arrangement

Whereby a party sells gas at the wellhead to a party with priority space in the pipeline queue and then repurchases the gas downstream, paying transmission costs and any prearranged differentials.