Diesel may appear to be a single product, but different grades and specifications are designed for different vehicles, machinery and applications.
Terms such as DERV, EN 590, B7, gas oil and HVO can make choosing a fuel seem more complicated than it needs to be. However, understanding a few key differences can help businesses order the correct fuel, protect their equipment and remain compliant.
This guide explains the main diesel grades available to UK businesses and where each can be used.
Understanding diesel grades in the UK
A diesel grade tells you about the composition, quality and intended use of a fuel. Some grades are developed for road vehicles, while others are suitable for specific off-road machinery or offer an alternative to conventional fossil diesel.
The main options covered in this guide are:
- EN 590 road diesel, also known as DERV
- B7 diesel
- Gas oil, commonly called red diesel
- HVO fuel meeting the EN 15940 standard
Although these fuels may be used in similar types of diesel engine, they are not automatically suitable or legally permitted for every application.
EN 590: The standard for road diesel
EN 590 is the recognised fuel standard for automotive diesel used in UK road vehicles. It sets requirements for factors including fuel quality, sulphur content, ignition quality and cold-weather performance.
Diesel supplied for use in road-going vehicles is commonly known as DERV, which stands for Diesel Engine Road Vehicle. It is used across a wide range of commercial fleets, including:
- HGVs
- Vans
- Cars
- Coaches
- Road going agricultural vehicles
EN 590 helps ensure that the fuel performs consistently and is suitable for modern diesel engines and emissions-control systems.
For fleet operators, DERV is the standard choice for vehicles used on public roads unless the vehicle manufacturer has approved another fuel, such as HVO.
B7 diesel and biofuel content
B7 is not a completely separate diesel grade from EN 590. It is the label used to show that diesel can contain up to 7% biodiesel, normally in the form of Fatty Acid Methyl Ester, or FAME.
The remaining content is standard diesel derived from crude oil.
B7 labels are displayed inside a square on fuel pumps and vehicle filler caps, helping drivers identify compatible fuel. The Department for Transport introduced the label to make the biofuel content of road diesel clearer.
Most diesel vehicles operating in the UK are designed to run on B7, but operators should always follow the vehicle or equipment manufacturer’s fuel requirements.
Gas oil and red diesel for eligible applications
Gas oil is a diesel fuel that has traditionally been used in off-road machinery, heating and power generation. When supplied at a reduced rate of fuel duty, it contains a red marker and is commonly called red diesel.
The colour does not determine its engine performance. It identifies the fuel as rebated and allows HMRC to detect where it has been used.
Red diesel can only be used in eligible vehicles, machinery and applications. These include certain uses connected with agriculture, horticulture, forestry, rail transport and non-commercial heating and electricity generation.
Eligibility depends on both the type of machine and how it is being used. A vehicle’s classification alone does not necessarily make it eligible.
The rules changed significantly in April 2022, removing entitlement from several sectors and applications. Businesses should therefore check the latest HMRC guidance on rebated fuels rather than relying on how red diesel was used in the past.
Using red diesel for an ineligible purpose can result in the fuel or equipment being seized and financial penalties being applied.
HVO as an alternative to conventional diesel
Hydrotreated Vegetable Oil, better known as HVO, is a paraffinic diesel fuel made from renewable raw materials. Unlike conventional road diesel, which meets EN 590, HVO is generally produced to the EN 15940 specification.
HVO can be used in many diesel engines without mechanical modification, but only where it has been approved by the original equipment manufacturer. Compatibility should always be confirmed before changing fuel.
For suitable vehicles and machinery, HVO can provide businesses with a way to reduce lifecycle greenhouse gas emissions while continuing to use existing diesel-powered assets.
Potential applications include:
- Commercial vehicles
- Agricultural machinery
- Construction equipment
- Generators
- Industrial machinery
HVO can also offer good storage stability and cold weather performance. However, businesses should consider availability, cost and manufacturer approval when deciding whether it is suitable for their operations.
Why diesel grades change with the seasons
Diesel performance can be affected by low temperatures. As the temperature falls, wax crystals can begin to form in the fuel, potentially restricting filters and interrupting the flow of fuel to the engine.
Fuel specifications are adjusted seasonally to improve performance in the expected temperatures. Winter grade diesel is formulated to remain usable at lower temperatures than summer-grade fuel.
This transition is normally managed through the fuel supply chain, so businesses do not need to request a different grade for each season. However, fuel stored for long periods can remain in a tank after the season changes.
Businesses with lower fuel turnover should monitor stored fuel, keep tanks properly maintained and plan ahead before winter. This is particularly important for machinery or generators that must remain available during cold weather.
Can different diesel grades be used interchangeably?
Not every fuel described as diesel is interchangeable.
EN 590 road diesel is suitable for standard diesel road vehicles, while red diesel is restricted by fuel duty rules. HVO is a drop in alternative meaning it works in many of the same engines, but its use remains subject to manufacturer approval.
Before changing fuel, businesses should consider:
- The manufacturer’s specifications
- Vehicle and machinery warranties
- The fuel standard required
- Red diesel eligibility
- Storage arrangements
- Seasonal operating conditions
- Any emissions or sustainability objectives
Price should not be the only consideration. Using an unsuitable fuel could affect performance, damage equipment, invalidate a warranty or place the business in breach of fuel duty rules.
Choosing the correct diesel for your business
The right diesel grade depends on what you are fuelling and how that equipment is used.
Road fleets will generally require EN 590 DERV. Eligible agricultural and specialist applications may be permitted to use red diesel, while HVO may provide an alternative for businesses looking to reduce lifecycle emissions without immediately replacing diesel powered equipment.
If you operate a mixture of vehicles and machinery, it is especially important to keep fuels clearly identified and stored separately. This helps prevent misfuelling and reduces the risk of rebated fuel entering equipment that is not entitled to use it.
Oilfast supplies commercial fuels to businesses across a wide range of sectors, including transport, agriculture and construction. Our team can help you identify an appropriate fuel for your application and arrange a reliable delivery around your operational requirements.
Get in touch with our team to discuss your commercial diesel, gas oil or HVO requirements.
