Degrees American Petroleum Institute-a measure of oil density.
API gravity API gravity equals 141.5 degrees divided by specific gravity at 60 defrees F, minus 131.5 degrees


A geological depression filled with sediments. Several basins of different ages overlying each other are referred to as stacked basins (e.g. Cooper/Eromanga Basins).


The process by which a finished well is either sealed off or prepared for production.


A liquid mixture of pentane and heavier hydrocarbons that is recoverable from a gas well through a separation system.

Crude oil

A mixture of hydrocarbons that existed in the liquid phase in natural underground reservoirs and remains liquid at atmospheric pressure after passing through surface separating facilities.

Demonstrated resources

The amount of petroleum that can be recovered from the part of identified resources whose existence is established and whose quantity is considered probable, based on well data and geological projection. In this publication, demonstrated resources are taken to be equal to remaining, proved plus probable, commercial and non-commercial reserves of petroleum as maintained at Geoscience Australia.


Phase of the petroleum industry in which a proven oil or gas field is brought into production by drilling production wells.


The first well (in a new field) from which any measurable amount of oil or gas has been recovered. A well that makes a discovery is classified as a new field discovery (NFD).


The phase of operations in which a company searches for oil or gas by carrying out detailed geological and geophysical surveys followed up where appropriate by exploratory drilling in the most promising places.

Extension/appraisal wells

Wells drilled to determine the physical extent, reserves and likely production rate of a field.


Including both permeable and non-permeable intervals.

Identified resources

The total amount of petroleum that can be recovered from specific accumulations that have been identified by drilling.

Initial resources

Resources before subtraction of cumulative production.


Liquefied natural gas, gaseous at normal temperature and pressures, but held in the liquid state at very low temperatures to facilitate storage and transport.


Liquefied petroleum gas, a liquid mixture of all the propane and butane that are recoverable from a well through a separating facility.

Natural gas

A mixture of methane and ethane and up to 3 per cent of carbon dioxide.

New-field wildcat well

A petroleum exploration well drilled on a structural or stratigraphic trap that has not previously been shown to contain petroleum.


A naturally occurring hydrocarbon or mixture of hydrocarbons. As oil or gas or gas in solution, it is widespread in Australian sedimentary rocks, but major concentrations are generally rare.

Petroleum resources

The part of Australia's petroleum endowment that may be produced profitably by currently feasible or near-feasible technology and for specified product prices. Petroleum resources are defined to include only those natural concentrations from which economic extraction of a part is feasible within the range of technology and prices likely to be seen within the next 20 to 25 years. Hence, petroleum resources are a subset of petroleum endowment that can change according to the assumed technological and economic conditions.


The phase of bringing well fluids to the surface and separating them and storing, gauging and otherwise preparing the product for transportation.

Production test

A test on a cased well whereby the nature and quantity of the formation fluids in a possible oil or gas bearing stratum are determined by allowing them to flow to the surface through the drill string under carefully controlled conditions.


Likely to contain producible petroleum.

Proved and probable reserves

Reserves established at the median value-that is with a 50% cumulative probability of existence.

Remaining resources

Resources after subtraction of cumulative production from the initial amount of resources.

Repeat formation test

Test run on a wireline in a well, to measure the pressure and temperature of the specific depths and to take small fluid samples from the reservoir.


Amount multiplied by the probability of existence.

Success rate

A ratio obtained by dividing the number of new-field discoveries by the number of new-field wildcat wells drilled.


Any barrier to the upward movement of oil or gas, allowing either or both to accumulate.

Undiscovered accumulation

A general term representing all undiscovered petroleum deposits irrespective of economic potential.

Undiscovered field

All of the petroleum accumulations that may occur in multiple reservoirs within the same structural or stratigraphic trap.

Undiscovered resources

The amount of conventional petroleum that can be recovered from unspecified accumulations that have not been identified by drilling, but may exist within a specific reservoir sequence wherever it lies within a structural or stratigraphic trap.

Topic contact: Last updated: May 31, 2012