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Ambient Temperature: The temperature of the surrounding medium such as the atmosphere.

API: American Petroleum Institute.
API Gravity (Relative Density): A means used by the petroleum industry to express the density of petroleum liquids. API gravity is measured by a hydrometer instrument having a scale graduated in degrees API.  The relation between API gravity and relative density (formerly called specific gravity) is: API Gravity at 60 Deg. F. = (141.5 : Relative Density 60F/60F) – 131.5

ASTM: American Society for Testing Materials. Grade and quality specifications for petroleum products are determined by ASTM test methods.

Barrel: The standard unit of liquid volume in the petroleum industry. It is equal to 42 U.S. gallons.

BS & W: Bottom sediment and water.

Bunkers: Fuel for a vessel. The type will vary depending upon the propulsion mode of the vessel. Steamships will use a heavy fuel oil, diesels use a range of fuels from heavy to light, and gas turbines generally use kerosene

Cargo Pump: Pump used on tankers for discharging cargo and loading or discharging ballast. Located, at the bottom of the pump room, these pumps are usually of the common duplex type, or turbine type of which the centrifugal is the most common.

Clingage: The residue that adheres to the inside surface of a container, such as a ship’s tank or shore tank, after it has been emptied.

Closed Gauging System: A method of obtaining measurements of the tank contents without opening the tank. This may be accomplished by using automatic tank gauges or by taking measurements through a pressure/vapor lock standpipe. This type of gauging is done extensively on vessels with inert gas systems. Such a system that allows no vapors to be lost to the atmosphere is a true closed system while other types that allow minimum vapors to be lost to the atmosphere are called “restricted systems.”

Density: Density is the term meaning the mass of a unit of volume. Its numerical expression varies with the units selected.

Dip: A term used to designate either the depth of liquid in a storage tank or the taking of the measurements of such liquid level. (See Gauging)

Floating Roof Correction: The correction made to offset the effect of the displacement of the floating roof, when no correction has been built into the tank capacity table.

Free Water (FW): The water present in a container that is not in suspension in the contained liquid (oil).

Gauging:  A process of measuring height of a liquid in a storage tank usually using a weighted graduated steel tape and bob.

Gross Observed Volume (GOV):  The total volume of all petroleum liquids and sediment and water, excluding free water, at observed temperature and pressure.

Gross Standard Volume (GSV):  The total volume of all petroleum liquids and sediment and water, excluding free water, corrected by the appropriate volume correction factor (Ctl) for the observed temperature and API gravity, relative density, or density to a standard temperature such as 60°F or 15°C and also corrected by the applicable pressure correction factor (Cpl) and meter factor.

Inert Gas (IG): A gas used by marine tank vessels to displace air in cargo tanks to reduce oxygen content to 8 percent or less by volume and thus reduce possibility of fire or explosion. The inert gas used is usually nitrogen, carbon dioxide or a mixture of gases such as flue gas.

Innage: The amount of space within a tank that is occupied by oil. Innages are sometimes called soundings or body gauges.

List or Heel:  The leaning or inclination of a vessel expressed in degrees port or starboard.

List (Heel) Correction:  The correction applied to the observed gauge or observed volume when a vessel is listing, provided that liquid is in contact with all bulkheads in the tank.  Correction for list may be made by reference to the vessel’s list correction tables for each tank or by mathematical calculations.

Load on Top (LOT): defined as both a procedure and a practice. Procedure: Load on top is the shipboard procedure of collecting the settling water and oil mixtures, resulting from ballasting and tank cleaning operations (usually in a special slop tank or tanks), and subsequently loading cargo on top of the slops and pumping the resultant mixture ashore at the discharge port. Practice: Load on top is the act of commingling onboard quantity with cargo being loaded.  The onboard quantity is the remnant of the previous cargo or part load into the tank.

Net Standard Volume (NSV): The total volume of all petroleum liquids, excluding sediment and water and free water, corrected by the appropriate volume correction factor (Ctl) for the observed temperature and API Gravity, relative density, or density to a standard temperature such as 60°F or 15°C and also corrected by the applicable pressure correction factor (Cpl) and meter factor.

Net Standard Weight (NSW): The total weight of all petroleum liquids, excluding sediment and water and free water, determined by deducting the S&W weight from the Gross Standard Weight (GSW).

Non-liquid volume: the measurable amount of material that is not free flowing at the time of measurement. Non-liquid material may include anyone or a combination of hydrocarbon waxes, water/oil emulsions, sediment, or solidified cargo.

OBQ (On Board Quantity): The material remaining in vessel tanks, void spaces, and/or pipelines prior to loading. On-board quantity includes water, oil, slops, oil residue, oil/water emulsions, sludge, and sediment.

Outage (Ullage): The depth of the space in a tank not occupied by oil. Same as ullage. It is measured from the flange of the ullage hole to the surface of the oil. Also the space left in a petroleum product container to allow for expansion as a result of temperature changes during shipment and use.

Petroleum: A generic name for hydrocarbons, including crude oil, natural gas liquids, natural gas and their products.

Portable Measurement Unit (PMU): A device designed to measure the ship’s cargo when its tanks are closed to the atmosphere. It is used in conjunction with a vapor control valve.

Portable Sampling Unit (PSU): A device designed to sample the ship’s cargo when its tanks are closed to the atmosphere. It is used in conjunction with a vapor control valve.

Reference Height: The distance from the tank bottom and/or datum plate to the established reference point or mark.

Reference Point (Gauge Point): The point from which the reference height is determined and from which the ullages/innages are taken.

ROB (Remain on Board): The material remaining in vessel tanks, void spaces, and/or pipelines after discharge. Remaining on board quantity includes water, oil, slops, oil residue, oil/water emulsions, sludge, and sediment.
Slops: are oil, oil/water/sediment, and emulsions contained in the slop tanks or designated cargo tanks. The mixture usually results from tank stripping, tank washing, or dirty ballast phase separation.

Sludge: Deposits in fuel tanks and caused by the presence of wax, sand, scale, asphaltenes, tars, water, etc.

Specific Gravity: Weight of a particle, substance or chemical solution in relation to an equal volume of water at 15C. Abbreviated as Sp.Gr.

Total Calculated Volume (TCV): The total volume of all    petroleum liquids and sediment and water, corrected by the appropriate volume correction factor (Ctl) for the observed temperature and API gravity, relative density, or density to a standard temperature such as 60°F or 15°C and also corrected by the applicable pressure factor (Cpl) and meter factor, and all free water measured at observed temperature and pressure (gross standard volume plus free water).

Total Observed Volume (TOV): The total measured volume of all petroleum liquids, sediment and water, and free water at observed temperature and pressure.

Trim Correction: The correction applied to the observed gauge or observed volume in a vessel’s tank when a vessel is not on an even keel provided that the liquid is in contact with all bulkheads in the tank. Correction for trim may be made by referencing trim tables for each tank or by mathematical calculation.

Ullage: See Outage
Ullages: Measurements taken with a steel tape from the lip of the ullage hole to the to the surface of the liquid; usually read to the nearest 1/8 inch.

Volume Correction Factor (VCF): the numerical value determined by laboratory analysis or by standardized computer arithmetic that when multiplied by the Gross Observed Volume at tank temperature results in the volume of the product at its standard temperature (15oC or 60oF). The factors applicable for bands of API (relative density) and temperature are available in standard tables booklets or may be computed using a standardized format.  If the VCF is below 1 it is shown accurate to 5 places of decimal otherwise it is shown in 4 places of decimal.

Vessel Discharge Ration (VDR): the total calculated volume (TCV) by the vessel measurement on arrival, less remaining on-board (ROB), divided by the TCV by shore measurement at discharge. VDR = (TCV on arrival – ROB) / TCV received from shore at discharge

Vessel Experience Factor (VEF): A factor based on the compilation of the history of the total calculated volume (TCV) vessel measurements, adjusted for on-board quantity (OBQ) or remaining on board (ROB), compared with the TCV shore measurements. This factor if developed according to the latest industry standards may be used to obtain a better ship shore comparison of volumes.

Vessel Load Ration (VLR): the total calculated volume (TCV) by the vessel measurement upon sailing, less on-board quantity (OBQ), divided by the TCV by shore measurement at loading. VLR = (TCV on sailing – OBQ) / TCV received from shore at loading

Water/Cut Measurement: The procedure of locating the oil/water interface for the purpose of determining the volume of free water in a shore tank or vessel compartment. It is also used to refer to the line of demarcation of the oil/water interface.

Wedge Formula: A mathematical means to approximate small quantities of liquid and solid cargo and free water on board prior to loading and after discharge based on cargo compartment dimensions and vessel trim. The wedge formula is to be used only when the liquid does not touch all bulk heads of the vessel’s tanks.

Wedge Table: a pre-calculated vessel table based on the wedge principle and displayed much like the vessel’s usual ullage/innage (sounding) tables.  These tables, however, are for small quantities (on-board quantities, remaining on board), when the cargo or free water does not touch all the bulkheads of the vessel’s tank.

Weight Correction Factor (WCF): the numerical value determined by laboratory analysis or by standardized computer arithmetic that when multiplied by the Gross Standard Volume results in the weight of the product. The factors applicable for bands of API (relative density) are available in standard tables booklets or may be computed using a standardized format.