Glossary of technical terms

Natural Gas (NG)

A combustible natural gas that is a mixture of gaseous hydrocarbons from underground deposits that formed through the decomposition of organic substances between layers of the earth’s crust. It can be extracted independently or in conjunction with the extraction of crude oil. Its main component is methane, while it also comprises heavy hydrocarbons, ethane, propane and butane, as well as steam, helium, nitrogen, hydrogen sulphide and carbon dioxide. It is used in industry and households for heating, for the production of electricity and as a motor fuel (CNG). It travels from deposits to users via underground pipelines. In Slovenia, its volume is measured in standard m3 (Sm3, 15 degrees°C and 1.01325 bar).

Liquefied Natural Gas (LNG)

Liquefied natural gas (LNG) is a natural gas cooled to a temperature of -161.6°C (111.55 K), at which the basic component of natural gas (i.e. methane) liquefies. Although it must be kept at a very low temperature, liquefied natural gas is more suitable for (ship) transport than natural gas in a gaseous state. Up to a distance of close to 4,000 km, the transmission of natural gas via pipelines under high pressure (up to 100 bar) is cheaper than the transport of LNG by ship. If a pipeline must be laid under the sea, the distance at which costs are equalised is shorter.

At an atmospheric pressure of 1 bar, the volume of LNG is 600 times lower than natural gas in its gaseous state. LNG is transported by sea using special tankers with insulated reservoirs. At gas terminals, it is converted back to its gaseous state by heating, while the pressure of the gas is increased so that it is suitable for transmission by pipeline.

Compressed Natural Gas (CNG)

Compressed natural gas is natural gas that is compressed in cylinders or reservoirs to less than 1% of its volume. It is used as a motor fuel. Its importance is increasing due to the fewer harmful emissions it releases than liquid fuels.

Liquefied Petroleum Gas (LPG)

A mixture of hydrocarbons that, at a normal temperature and pressure, are the gaseous by-product of refineries. They are first separated from crude oil in the distillation process, as they comprise low levels of saturated paraffin hydrocarbons, in particular propane and butane. For easier transport or storage, they are fully or partially liquefied. They are kept in a liquid state using high pressure or low temperatures. At normal atmospheric pressure, they return to their gaseous state. LPG is used for cooking and heating, and as a motor fuel. LPG is filled, stored and transported in pressurised receptacles (cylinders, barrels and containers). Liquefied propane and butane are filled in cylinders separately or as a mixture. In their gaseous state, they are heavier than air. For this reason, pressurised cylinders may not be stored in places where the floor is lower than the surrounding terrain.

Calorific Value (CV)

Measurement of the amount of energy released in the form of heat when fuel (natural gas) is burned. The units for gaseous fuels, kJ/m3 and kWh/m3, are used to measure gross calorific value or net calorific value. Gross calorific value includes the heat generated in the condensation of steam in flue gases and in transformation to a liquid state. In contrast to net calorific value, which does not include this, the average gross calorific value of natural gas in Slovenia is 37,968 kJ/Sm3.


Underground storage facilities in porous, natural or man-made geological formations such as abandoned mines, exhausted crude oil or gas wells, underground caverns and storage reservoirs.


Maximun stream (q) expressed in cubic meters per time per unit (day, hour) to which the consumer is entitled according to their agreement on supply of natural gas, access to transmission system or transport of natural gas.

Balance group

Group of one or more market players formed by the supplier of natural gas to a reception point in the natural gas transmission network in the Republic of Slovenia for sales to end customers at delivery points.

Transmission Network System Operator (TNSO)

Natural gas transmission network system operator and responsible for providing system services, and the secure and reliable functioning and maintenance of the natural gas system, which it links to other systems.

Distribution Network System Operator (DNSO)

Operator of the natural gas distribution network, responsible for the functioning, maintenance and development of the network, and for providing other services related to the distribution network, as prescribed by energy legislation.


Service of natural gas transmission network system operator, which corrects imbalances between the actual supply and consumption of natural gas for an individual user (balance group).

Crude Oil

The crude oil found in nature is an oily, yellow to dark grey liquid that forms from organic substances. It comprises close to 3,000 different compounds, mostly (more than 80%) carbon. It is a mixture of gaseous, liquid and solid substances. Hydrocarbons of very different compositions are pumped from below the earth’s surface. Associated gases are separated from crude oil, which is then processed in a refinery. At ambient temperature and atmospheric pressure, crude oil takes a liquid form. It is most frequently divided into groups according to its viscosity: light, medium, heavy and extra heavy. Crude oils are generally divided into those from the Middle East and countries of the former Soviet Union (medium and heavy), from Western and Northern Africa and the North Sea (light) and from South America (heavy).

Barrel (BL, BBL, B)

Unit of volume measure used for crude oil and crude oil products. One barrel equals approximately 159 litres which is equal to 42 US gallons (1 US gallon = 3.78 litres). The unit derives from the 19th century, when the US began producing for the market. Extracted crude oil was stored in wooden barrels.

Fuel Oil

Liquid heating fuel can be broken down by sulphur content into low sulphur-content fuels (less than 1%) and high sulphur-content fuels (1% or more).

Gas Oil

Liquid fuel for diesel motors in cars, cargo vehicles and ships (diesel fuel), and heating fuel for industry and general consumption (extra light heating oil). It is extracted through the fractional distillation of crude oil.

British Thermal Unit (BTU)

Unit for measuring the amount of heat: 1 BTU = 1,055 J

Tonnes of Oil Equivalent (TOE)

Agreed unit for converting various types of energy into a common denominator:

  • 1 TOE = 10,034 Mcal
  • 1,000 m3 of natural gas = 0.857 TOE
Load Factor (LF)

Ratio of average consumption to peak consumption of a customer in a given period.

Daily LF is calculated using the following formula:


Hourly LF is calculated using the following formula:


q = capacity (Sm3/day)

Q = quantity of natural gas used (Sm3/year)

Natural gas

  • Natural gas-powered vehicles are more environmentally friendly.

    Natural gas-powered vehicles produce 20% to 30% less CO2 emissions. More
  • Natural gas releases 20% to 50% less CO2.

    Natural gas releases 25% to 50% less CO2 per unit of energy generated for home heating or industrial purposes. More
  • Natural gas has a higher conversion factor.

    Natural gas is more efficient than other fossil fuels in the production of electricity or heat. More
  • Natural gas achieves a high efficiency rate.

    Natural gas can achieve an efficiency rate of nearly 100%. More
  • What is natural gas?

    Natural gas is a fossil fuel formed by the decomposition of organic substances. More
  • Natural gas can be as much as 100 million years old.

    The age of natural gas derives from the decomposition of prehistoric animals and plants. More
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