Glossary

Here is an alphabetical listing of terms used throughout this site. Use the alphabetical picker below to display only the terms beginning with your chosen letter.

Alkylation

A process for manufacturing high octane blending components used in unleaded petrol or gasoline (RON 95,97,98).

Aromatics

These are the range of hydrocarbons which have a distinctive sweet smell and include benzene and toluene. They naturally occur in petrol and are also extracted as a petrochemical feedstock, as well as for use as solvents.

Barrel

A volume measurement of crude oil. 1 barrel = 42 gallons (US) or about 35 gallons (imperial) or 159 litres

Benzene

See Aromatics

Biofuels

The description “biofuel” is a generic one used to describe liquid or gas fuels that are not derived from petroleum based fossils fuels or contain a proportion of non fossil fuel. Biofuels fall into two main categories- conventional biofuels produced from plants, crops such as sugar beet, rape seed oil or re-processed vegetable oils - and advanced biofuels from gasified biomass. At present, most biofuels fall into the conventional category.

Biomass

A term used to describe trees (woody biomass) or crops such as wheat or corn, grasses and waste organic material (non-woody biomass) which can be used to produce heat and power. 

Bitumen

A very heavy residue, black in colour, solid or semi-solid at room temperature. It is most commonly used as a road surface or in roofing materials.

Catalyst

A substance that accelerates a chemical reaction without itself being affected. In refining, catalysts are used in the cracking process to produce blending components for fuels.

Cetane number

A measure of the ignition quality of diesel fuel; the higher the number the more easily the fuel is ignited under compression.

Cracking

A secondary refining process that uses heat and/or a catalyst to break down large chemical components into smaller, lighter ones which can be used as blending components for fuels.

Crude oil

An unrefined mixture of naturally occurring hydrocarbons, whose densities and properties vary widely. Crude oils contain sulphur, nitrogen, oxygen, as well as traces of metals such as vanadium or nickel. Crudes like North Sea Brent which are low in sulphur are often referred to as "sweet" and their properties are more highly valued.

Diesel or derv

Light hydrocarbon mixture slightly heavier than kerosene used in engines which ignite fuel through compression generated heat rather than spark ignition as in a petrol engine. The term derv is derived from the expression "diesel engine road vehicle"

Distillate

Any petroleum product produced by boiling crude oil and collecting the vapours produced as a condensate in a separate vessel. Most refinery products can be classed as distillates; for example petrol (light distillate), gas oil (middle) or fuel oil (heavy)

Distillation

The primary distillation process which uses high temperature to separate crude oil into vapour and fluids which can then be fed into a distillation or fractionating tower.

Fractionating

Another name for distillation.

Fuel cell

A process that converts chemical energy in a fuel such as, gas, petrol or hydrogen into electric current either to drive an electric motor (vehicle application) or to generate  power.

Fuel oil

A heavy residue, black in colour, used to generate power or heat by burning in furnaces.

Gas to Liquids (GTL)

The production of liquid fuels from natural gas, coal or biomass, often using a process known as Fisher-Tropsch, or developments thereof, that was first demonstrated in the early 1920s.

Gasoil

A middle distillate used in diesel engines or as heating fuel.

Gasoline

Commonly called petrol in the UK, gasoline or motor spirit is a volatile, flammable liquid hydrocarbon refined from crude oil and used to fuel spark ignition internal combustion engines.

Ground level ozone

Naturally accurring compound which is also formed by the interaction of VOCs, NOx and sunlight, giving rise to smog and poor low-level visibility, particularly during hot sunny spells.

Hybrid vehicles

Vehicles which employ both petrol/diesel and electric engines in combination with regenerative braking/battery charging for improved fuel efficiency and low emissions

Hydrocarbons

Organic compounds of hydrogen and carbon whose densities and boiling and freezing points increase as their molecular weights increase. The smallest hydrocarbon molecules are gaseous in form and the largest solid.

Hydrogen

Flammable colourless gas occurring in water and most organic compounds. When extracted it can be burnt in an internal combustion engine or used in a fuel cell. However liquifying the fuel and storing it under high pressure consumes a high proportion of the energy value of the fuel.

Isomerisation

The process of altering the arrangements of atoms in a molecule without adding or removing anything from the original material.

Kerosene

A light middle distillate that in various forms is used as aviation turbine fuel (Avtur), for burning in heating boilers or as a solvent, such as white spirit.

Leaded petrol

Until the advent of exhaust catalyst equipped vehicles in the early 1990s, leaded petrol in 4* of 97 octane was the main form of petrol in the UK. Tetra ethyl or tetra methyl lead additives were used as a simple means of boosting octane and providing the necessary lubrication to prevent excessive wear of cylinder head valve seats. Leaded petrol was banned in the EU from the start of 2000 and for a while Lead Replacement Petrol (LRP) was available in the UK until dwindling demand saw it largely disappear in 2004.

LPG

Liquified Petroleum Gas (LPG) is a light hydrocarbon - bottled gases butane and propane and auto motive LPG (often called autogas) are examples- which is gaseous at normal room temperature and atmospheric pressure. Easily liquefied under pressure for storage and transportation, it rapidly returns to gas on release of pressure.

LRP

Lead Replacement Petrol (LRP) was widely introduced at the start of 1999 in response to EU legislation which prohibited the use of leaded petrol as a mainstream fuel from the end of that year. LRP has an octane rating of RON 97 and uses an additive to provide the valve seat lubrication properties previously provided by lead. By the end of 2002 demand for LRP declined to a very low level and started to be phased out from some filling stations and largely disappeared in 2004.

MTBE

Metyl tertiary butyl ether is highly refined high octane light distillate used in the blending of petrol.

Naphtha

A volatile, flammable light distillate used to make petrol and as a solvent.

Nitrogen oxides (NOx)

Formed during combustion of petrol, diesel, gas oil and fuel oil with the interaction of nitrogen in the fuel and oxygen. NOx is associated with ground level ozone formation. 

Octane number

A measure of petrol's resistance to pre-ignition or "pinking", which is the sound made by an engine when pre-ignition occurs, particularly at low revs and high load. Two measures are used, for low speed and high speed pre-ignition. ULSP in the UK typically has a MON (Motor Octane Number) of 85 and a RON (Research Octane Number) of 95. SULSP and LRP have a RON of 97/98.

Olefins

The group of hydrocarbons known as alkenes. Refinery olefin units produce ethylene and propylene to make polyethylene and polypropylene, used by the petrochemical industry to make plastics, synthetic fibres and adhesives.

Petrol

Something you run your car on.

Petroleum

Another term used for the family of hydrocarbons which make up crude oil.

Polymerisation

Bonding two or more simple molecules together under heat and pressure to form larger molecules, typically used in the manufacture of plastics. 

Reforming

A refining process used to change the molecular structure of a naptha feed derived from crude oil by distilation.

Residue refining

The term used to descibe a number of processes to upgrade fuel oil to catalytic cracker feed, for example by using pressurised hydrogen gas and a catalyst.

Sulphur

Pale yellow non-metallic chemical element naturally occurring in crude oil. Reduction of sulphur content in fuels is desirable for corrosion control and for the efficient functioning of exhaust catalysyts.

Sulphur dioxide (SO2)

Formed during combustion of fuels such as diesel or gas oil. SO₂ contributes to acid rain.

Sulphur-free fuels

Term used to describe the latest petrol and diesel fuels with a sulphur content of 10 part per million or less. These fuels are designed to optimise the performance of new engine and exhaust clean up technologies such as gasoline direct injection and de-Nox catalysts. 

Toluene

See Aromatics

Tonne

A metric tonne equivalent to 1,000 kilograms or in crude oil terms about 7.5 barrels of oil.

Vacuum distillation

A secondary distillation process which uses a partial vacuum to lower the boiling point of residues from primary distillation and extract further blending components

Volatile Organic Compounds (VOCs)

Name given to light organic hydrocarbons which escape as vapour from fuel tanks or other sources, and during the filling of tanks. VOCs contribute to smog.