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Posted on: 22/05/2017

What is Gas Oil? CPS Fuels Information Sheet

What is Gas Oil? CPS Fuels Information Sheet


Gas Oil is a middle distillate liquid refined from crude oil. It has many different names in the UK and a variety of uses. Gas Oil is a "dual purpose" fuel. It has a high calorific value (heat content) and is thus recommended as a boiler fuel in industrial or agricultural installations with pressure jet burners e.g. grain dryers. It can also be used in a diesel engine fuelling off-the-highway equipment such as farm tractors, construction equipment, railway and marine engines, and stationary diesel engines or generators. It can be called: Gas Oil, Red Diesel, Farm Diesel, ULSG, Class A2 or Class D, 35 second burning oil, Marked EN590.

A lot of the confusion around Gas Oil, and the variety of different names, has come both from its variety of different uses, and changes to product specification over the last few decades. We will expand on this later.

Why is Gas Oil Red?

All liquid fuels in the UK are subjected to a rate of excise duty by HM Customs & Excise. Road fuels, Petrol and Diesel have high duty rates applied to them, but other non-road fuels have lower or zero duty rating applied. As Gas Oil is a form of diesel it can be used in diesel engines to provide propulsion or generation.

Gas Oil is a 'rebated' fuel, (reduced rate of excise duty), and the permitted use of any rebated fuel is controlled by HM C & E. Gas Oil is permitted for use in Tractors, hence Tractor Diesel, and on Farms, hence Farm or Agricultural Diesel, and is marked with a red dye to reflect this. The red dye contains chemical markers in accordance to Customs and Excise requirements and so its illegal use can be easily detected. The use of the Red dye has led the one of the most recognisable names for Gas Oil – Red Diesel.

Road Diesel (DERV) is not dyed and so is sometimes known as White Diesel. A tiny amount of Red dye from Gas Oil or Red Diesel, mixed accidently or on purpose to avoid paying duty, is easily detected by HM C & E.

Red Diesel sample from a pump

Has Gas Oil specification changed?

Environmental Legislation has demanded cleaner fuels with less harmful emissions and the British Standard for Gas Oil has changed specification to meet this. Sulphur was identified as one of the most harmful components of Gas Oil, but was historically needed as a lubricant within the fuel.

What's the British Standard for Gas Oil?

Since 2006, the British Standard for Industrial Fuel Oils, BS2869:2006, contains two grades of Gas Oil; Class A2 & Class D. The Class A2 specification is suitable for both diesel engines and furnace applications whilst the Class D specification is only suitable for furnace applications such as boilers, dryers and roadstone coating plants, but not suitable for diesel engines. In simple terms Class A2 is a low sulphur product, with the necessary lubricant requirements being replaced by additives, and Class D is much higher in sulphur, so “dirtier” when burnt.

As very few engines or burners can now legally use Class D fuel, the fuel industry has concentrated on making, storing, and distributing Class A2. From a consumers perspective most applications can use Class A2 without any cost or performance implications.

What is EN590?

EN 590 is the current standard for all automotive diesel fuel sold in the European Union member states. It is published by the European Committee for Standardization and it describes the physical properties of the fuel. It was introduced to partner the European emission standards as part of the drive for a cleaner environment. All Road Diesel (DERV) now sold in the UK meets the EN 590 standards, and because it has a low sulphur content is also called called ultra low sulphur diesel (ULSD).

So what is my Gas Oil now?

Lets recap: There are two recognized standards of Gas Oil that are currently in use: BS 2869 Class A2 and BS 2689 Class D. Class A2 has a maximum sulphur content of 10ppm and is used for off road vehicles and equipment, while Class D has a maximum sulphur content of 1000 ppm and can only be used for heating or static generators. Class A2 gas oil may be used for either application.

Red diesel to tank

Both Gas Oil and Road Diesel (DERV) are quite similar in chemical structure, but they differ in two ways that are impossible to tell by sight alone. Gas Oil has a lower cetane rating, so may have a lower energy yield than the DERV (vehicle diesel) alternative. The higher the cetane rating the shorter the ignition delay. A short delay produces a cleaner and more efficient fuel burn, with less emission and fewer deposits left in the engine’s fuel injection combustion chamber. Road Derv (EN590) has a compulsory Bio component blended into it, whereas this is optional for Gas Oil. EN590 exceeds all Gas Oil specification requirements and can be “downgraded” and called Gas Oil, whereas Gas Oil cannot be enhanced, e.g. by additives, and called EN590.

Oil Samples

In 2011 the Government changed their legislation as a result of EU pressure to decrease off highway emissions. So in 2011, it became a requirement that all fuel used in off-highway mobile machinery must comply with EU Ultra Low Sulphur Diesel (ULSD) regulations, and must therefore contain no more than 10mg of sulphur per kg of fuel. Since white road diesel (DERV) was already ULSD compliant at this time, it is often believed that the specifications for red diesel and white diesel have been identical since the regulation change, but the potential for the two differences – cetane and bio components remain.

Since the mid 2000’s diesel engine manufacturers have been designing engines to comply with the changes in environmental legislation, and all have sought to ensure they develop their engines to work on the most suitable fuel. In the UK it was found that some modern tractors suffered from poor performance because they were running Class A2 Gas Oil whereas they were designed to operate on fuel that met the higher BS EN590 white road diesel fuel specification. John Deere, in particular, specify that fuel used within their engines must comply with the higher BS EN590 white road diesel fuel specification in order to guarantee performance and avoid invalidating warranties.

Tractor & Combine for Gas Oil article 2

Since the change is legislation, and because the majority of Gas Oil used in the UK goes into the Agricultural and Commercial markets to power engines, UK refiners and importers have focused on supplying the UK with diesel which meets the highest possible required European standard EN590.  When they decide which market the fuel is going into they with pay the full duty rate to HM C & E for Road Diesel, or they “downgrade” the EN590 specification fuel to Gas Oil by paying the reduced duty rate and putting the dye in to reflect it.

CPS Fuels, as a JET authorised distributor, supply marked EN590 grade diesel as Gas Oil so you have the highest quality Gas Oil available irrespective of use. CPS Fuels Gas Oil meets the same BS EN590 specifications as white road diesel and is therefore suitable for use in all farm machinery without the need for fuel treatments or additives.* The fuel properties of Gas Oil are adjusted seasonally to maintain good low temperature performance and operability. Gas Oil supplied from September onwards is winterised.

To order Gas Oil in Bulk or Barrels click or call CPS Fuels now.

We’re local, we’re best, we’re CPS.

*Note - Although CPS Fuels supplied Gas Oil meets the specification for white road diesel it is marked at source, carries the reduced rate of excise duty, and must not be used as road fuel. Both our suppliers, and CPS Fuels, reserve the right to alter the specification without notice. Nothing on this specification, or in this article, constitutes a guarantee.


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