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  • Writer's picturePinnock Brothers

Ultimate Guide to Red Diesel

Gas oil serves as a commercial fuel, offering an alternative to road diesel. Distinguished by its lower tax duty, this fuel adopts a distinctive red hue, earning it the moniker "red dye diesel." The red colour serves a crucial purpose in aiding HMRC in identifying its designated usage. In cases where there is suspicion of illegal use, particularly in vehicles operating on public roads, the tell-tale sign emerges as the red dye stains the fuel tank, unmistakably revealing its prior utilization within the vehicle.

Other terms such as 35-second oil, tractor diesel, and agricultural diesel are occasionally used to describe this fuel. Nevertheless, gas oil and red diesel stand out as the predominant and widely recognized names for this distinctive fuel.

red diesel being poured

Key Takeaways

  • Red diesel is a cheaper alternative to regular diesel and is commonly used in agricultural work.

  • Red diesel is illegal to use on public roads in the UK due to its high sulphur content, which causes pollution and contributes to acid rain.

  • HMRC has the power to inspect vehicles and impose fines or even imprisonment for illegal use of red diesel.

  • Individuals must sign an RDCO form upon purchase.

Qualifying Applications for Red Diesel Supply:

We are authorized to supply red diesel for the following specific applications:

  • Agriculture, Forestry, Horticulture, and Fish Farming: This includes machinery used in farming, forestry, horticulture, as well as vehicles utilized for cutting hedges, gritting roads, and performing flood and snow clearance.

  • Commercial Boating: Red diesel supply is available for fishing, inland water freight industries, and passenger ferries. (Excludes Northern Ireland)

  • Non-Commercial Heating: This encompasses the heating of non-commercial buildings such as homes, places of worship, town halls, and heating on permanently moored houseboats.

  • Circuses, Travelling Funfairs, and Circuses: Diesel for machinery, including caravans, used in circuses and travelling funfairs is included.

  • Non-Commercial Power Generation: Hospitals and off-the-grid households fall under this category, allowing them to use red diesel for power generation.

  • Passenger, Freight, and Maintenance Vehicles Designed for Rail Tracks: Red diesel can be utilized for vehicles operating on rail tracks.

  • Amateur Sports Clubs and Golf Courses: This includes ground maintenance, clubhouse heating, and lighting. Qualifying amateur sports clubs must be registered as community amateur sports clubs (CASCs).

How is Gas Oil Made?

Gas oil is typically derived from petroleum, constituting a fossil diesel obtained through the fractional distillation of crude oil. During this process, crude oil is introduced into a substantial chamber known as a fractionating column, where distillation occurs. In this column, the lower section experiences a more elevated temperature, which gradually cools as it ascends to the upper part. Various levels within the column feature differing temperatures, contributing to the cooling of the atmosphere towards the upper region. Multiple condensers, strategically positioned at various heights, capture vapours of distinct substances formed under corresponding conditions. Gas oil, being one of the denser substances produced, is gathered in proximity to the lower segment of the column.

Why is Red Diesel Regulated?

One of the major reasons for red diesel being regulated is its impact on air pollution. Red diesel has a higher sulphur content than regular diesel, which leads to the emission of sulphur dioxide. This harmful gas is a major contributor to air pollution and can lead to the formation of acid rain. Additionally, red diesel does not meet the government's environmental standards, making its usage detrimental to the environment.

Another reason for its regulation is the economic implications. Red diesel has a lower amount of tax than regular diesel, which means that it evades road maintenance funding. This has a negative impact on the overall infrastructure and maintenance of public roads.

Therefore, the illegal status of red diesel is justified due to its negative impact on both air pollution and the economy.

Individuals must sign an RDCO form upon purchase.

How Would You Get Caught Using Red Diesel Illegally?

In the UK, the HMRC has the authority to inspect any vehicle and conduct a thorough examination of its fuel tank. If a vehicle is found using red diesel illegally, it can be seized, and a release fee must be paid. The HMRC routinely scrutinizes the documentation of businesses involved in the sale of this commercial fuel.

Being caught using red diesel on public roads results in fines, the severity of which depends on the nature of the offence. Many individuals working on construction sites opt for red diesel to refuel their vans due to its lower cost compared to regular diesel. However, the distinctive red dye in red diesel can leave stains on the ground and equipment, making it easier for authorities to detect unauthorized use.

What Happens if You Get Caught?

Offenders can face fines, with repeat offenders and serious cases potentially facing imprisonment.


Eligible users, such as farmers can still use red diesel for their vehicles not intended for public road use. However, the emission of sulphur dioxide and the evasion of road maintenance funding have led to stricter regulations and penalties imposed by HMRC.


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