Let’s be honest. When was the last time you fueled your car with diesel and noticed its color? If you’re like most people, the answer is probably never.
Most people do not check the fuel color as it goes directly into their car through a nozzle. After all, as long as the car starts and gets them to their destination, what does the color matter?
Well, it does, as diesel fuel can actually come in a variety of different colors, depending on its intended purpose. And you don’t want to fill your car with the wrong kind.
What Color Is Diesel Fuel?
In the US, diesel fuel is available in three different colors – clear, blue-dyed, and red-dyed – each with its own designated purpose.
Regular diesel that’s found in every gas station is clear or amber in color hence the name, clear diesel. Clear diesel is meant for use by the everyday vehicles we see on the road, including cars, trucks, SUVs, and marine vehicles. It has a low sulfur content and is taxed accordingly.
Red-dyed diesel is fuel meant for off-road use only, such as tractors and construction equipment. Because it contains a higher sulfur content, it is not to be used in on-road vehicles and it’s not taxed.
Blue-dyed diesel is similar to red-dyed diesel in contents but it can only be used by U.S. Government vehicles.
Types of Diesel Fuel and Colors
With that said, you might still have a few questions about diesel fuel colors so let’s discuss each of the aforementioned diesel color variants in detail as well as some other diesel colors you might come across.
Cleared-colored or on-road diesel
Clear-colored diesel is what you’ll want to use for your on-road vehicles and it is readily available for sale at all gas stations.
It is also known as Ultra-Low Sulfur Diesel (ULSD) since it has a low sulfur content – no more than 15 parts per million (ppm).
In fact, the Environmental Protection Agency (EPA) enacted a rule in 2006 that all diesel fuels must have a sulfur content below 15 ppm. This was done in an effort to reduce emissions of nitrogen oxides and particulate matter.
Since clear-color diesel fuel is meant for on-road use, it is taxed similarly to gasoline. As of today, federal taxes on diesel include an excise tax of 24.3 cents per gallon and a Leaking Underground Storage Tank fee of 0.1 cents per gallon.
Red-dyed or off-road diesel
Most of the diesel fuel that is dyed in the U.S. comes with red coloring. It is not usually available for purchase by the public, but you may see it at a fuel station sometimes.
By law, red diesel fuel can only be sold for use in off-road vehicles like tractors, construction equipment, and generators.
Usually, industries like farming and construction, as well as commercial marine vessels use red fuels for off-road equipment.
The primary difference between clear and red-dyed diesel is sulfur content and density. Based on sulfur content, there are two classes of red diesel:
- Class A2: Sulfur content up to 0.001% (10ppm) and meant for all off-road vehicles such as trains or tractors, limiting
- Class D: Sulfuur content up to 0.1% (1,000 ppm) and suitable for seagoing marine vessels, stationary engines, static generators, and heating boilers.
In terms of density, dyed diesel has a significantly lower density of 0.81 grams per milliliter as compared to 0.85 grams per milliliter in clear diesel.
Red-dyed diesel fuel is not taxed within the United States because it is not supposed to be used for on-road purposes which makes it significantly cheaper than clear diesel.
Can red diesel damage my car?
No, not at all, using red diesel won’t damage your engine or any other part of the car. Red diesel is exactly the same as clear diesel, but with a red dye.
Technically, all diesel engines can run on red diesel, but it is illegal to be used by on-road vehicles and if caught you will be fined or prosecuted.
Can red diesel be made clear again?
Yes, it is possible to remove dye from red diesel and make it look like regular diesel but it’s a complicated process and leaves minute traces that lab testing can identify so it won’t be effective.
Moreover, removing dye from diesel fuel (aka fuel laundering) is a criminal offense at both the state and federal levels and you can receive hefty penalties if caught.
Blue-dyed diesel fuel is another type of non-taxed dyed diesel that is similar to red-dyed diesel, except it can only be used by U.S. government vehicles.
The main difference between red diesel vs blue diesel is that red diesel is for off-road vehicles while blue diesel is meant exclusively for U.S. government vehicles.
Green-dyed diesel fuel is available in some states for agricultural use only. It is dyed green to indicate that it’s meant for agricultural use and cannot be used for any other purpose.
Purple-dyed diesel fuel isn’t used officially but is obtained when red and blue diesel fuels are mixed together. Since it’s not an approved color, using purple-dyed diesel can result in a fine.
Diesel Fuel Color Chart
In a recent study, a group of experts tested the color of fossil diesel in its pure form and samples of fossil diesel containing biodiesel at 1 to 6% v/v.
As you can notice, pure fossil diesel is clear in color, and as the volume of biodiesel increases, the concentration intensities and leads to a color change.
Red Diesel vs Regular Diesel
There is no difference between red diesel and regular diesel in terms of quality or performance.
The main difference is that red diesel is meant for off-road use only, while regular diesel can be used for both on and off-road vehicles.
In terms of cost, red diesel is usually cheaper than regular diesel because it’s not subject to the federal excise tax.
There’s a misconception that using red diesel results in a loss of performance but that’s not the case and there’s no data to prove it.
However, since red diesel has higher sulfur content, it produces more emissions than regular diesel, which is why it’s not meant for on-road vehicles.
Why Does The US Government Regulate Diesel?
Diesel fuel is regulated by the US government because it’s a petroleum product and classified as a hazardous material. The government regulates diesel to ensure that it meets certain quality standards and is safe to use.
Diesel is also taxed by the government, which helps to fund transportation infrastructure and other programs. As a result, clear diesel meant for on-road vehicles has an excise tax,
Diesel fuel is subject to the federal excise tax, which is a tax imposed on certain products made from petroleum. The excise tax on diesel fuel is 24.4 cents per gallon, which is higher than the 18.4 cents per gallon excise tax on gasoline.
On top of that, each state has its own local taxes and fees as well. Every US state levies its own taxes in addition to the federal gasoline tax.
On average, US car owners pay 52.64 cents per gallon in gas taxes and 60.29 cents per gallon in diesel taxation. You can check the entire list of state motor fuel tax rates here.
The excise tax on diesel fuel is used to fund the Highway Trust Fund, which pays for transportation infrastructure projects such as road construction and maintenance.
Since off-road vehicles and other types of machinery used by farmers often do not use roads, governments regulate dyed diesel fuel as a way to ensure that it’s not used for on-road vehicles.
How is Diesel Fuel Made?
Diesel fuel is made from crude oil, which is a mixture of hydrocarbons. The process of making diesel fuel from crude oil is called refining.
During the refining process, crude oil is heated and turned into a mixture of gases and liquids. This mixture is then cooled and turned into different types of fuels, including diesel.
Diesel fuel typically contains about 15% more energy than gasoline. That means that it takes less diesel fuel to power a machine than it does gasoline.
Frequently Asked Questions
What color is normal diesel fuel?
Normal diesel fuel is typically clear or very pale in color. However, some types of dyed diesel fuel can be green, red, or purple.
What is the difference between red diesel and blue diesel?
The main difference between red diesel and blue diesel is that red diesel is for off-road vehicles while blue diesel is for only US government vehicles.
Can I use off-road diesel in my truck?
No, you cannot use off-road diesel in your truck. Off-road diesel is a type of dyed diesel that is meant to be poured into tractors, construction equipment, or even a generator and it’s not meant for on-road vehicles. Using off-road diesel in your truck is illegal and can result in a fine.
Is diesel fuel red or green?
Diesel fuel can be either red or green, depending on its intended use. Red diesel fuel should be used for off-road vehicles while green diesel fuel is used for agriculture vehicles in some states.
Can diesel fuel be different colors?
Yes, diesel fuel can be in different colors such as clear, red, blue, or green. However, for your regular vehicle, you can only use clear-colored diesel available at all gas stations.
Why is my state’s diesel tax so high?
Every state has its own gas tax rate in addition to the federal gasoline tax. Some states, like California, have a higher diesel tax because they use the revenue to fund their public transportation systems.
So, what color is diesel fuel? The answer is that it can be either clear, red, or blue, depending on its intended use.
Clear diesel is meant for on-road vehicles, while red diesel is only for off-road vehicles. Blue-dyed diesel is another type of non-taxed diesel that can only be used by U.S. government vehicles. Finally, green-dyed diesel is available in some states for agricultural use only.
I hope this article has helped clear things up for you. If you have any further questions, feel free to leave them in the comments below.
Robert Bacon is a car nerd and automotive lover who has dedicated his life to understanding the inner workings of vehicles. He holds a degree in mechanical engineering and has spent years working as a mechanic and engineer for some of the world’s top car companies. In his spare time, he enjoys writing about cars on this blog and tinkering with his 2016 Toyota Mirai in his garage.