Semi-trucks are incredible vehicles, built to travel long distances and transport all the goods we rely on. But so much about semi-trucks is unknown to the average person. Here we’ll tackle a common question and explain more about the gasoline used to power a semi-truck.

Diesel semi-trucks: A semi-truck uses diesel instead of gasoline in its engine. This is because diesel engines are tougher and better able to tow large loads. Diesel lasts longer and has a better mileage rate than gasoline. The average fuel efficiency for a semi-truck is only 5 miles per gallon, so it is very expensive to run the engine. However, there are newer semi-trucks on the market with an average of 8 to 10 miles per gallon, which will save truck drivers and their companies a considerable amount of money.

Are Semi Trucks Gas or Diesel?

Unlike most cars, which run on gasoline, semi-trucks use diesel. There are many reasons for this but note that almost all heavy transport vehicles use diesel.

While the price of gasoline and diesel has waxed and waned over the years, diesel is usually the cheaper option. Trucks travel a lot of miles, so any time you can save money, the better it is for a company’s bottom line.

Even if diesel is at the same price as gasoline, it is actually more efficient. You can create more units of energy out of diesel than you can with gas, which means you can travel more miles on diesel than on gas.

Diesel also has the advantage of producing a lower speed per torque. This increases the towing capacity of a truck, which is incredibly important as a semi-truck has to tow the massive trailer attached to it.

A diesel engine will also last longer than a gas engine. Due to the many miles that a semi-truck travels, a longer lifespan is imperative; otherwise, you would need to constantly replace the engine.

What are the negatives of using diesel?

As we can see, using diesel in a semi-truck is more about economics. Unfortunately, there are also some downsides to using diesel.

First, if you have ever been near a semi-truck, you will notice a difference in the noise level. Diesel engines are much noisier than gas engines.

This is because diesel engines rely on compression to ignite the fuel. In contrast, gasoline engines have spark plugs located in cylinders which muffle the noise.

Higher vibrations are produced with a diesel engine which results in more violent combustions. While diesel engines are not as loud as they used to be, they are still louder than gas engines, and far more louder than electric vehicles.

What kind of “gas” does a semi-truck use?

What kind of gas does a semi-truck use

A semi-truck uses diesel, not gas. There are different types of diesel and a semi-truck will usually use Diesel #2 (2-D).

The rating of diesel refers to the level of cetane present. Diesel #2 has a lower amount of cetane than Diesel #1, which makes it less volatile.

Semi-trucks carry heavy loads and drive for very long periods of time, so having fuel that is less volatile and less flammable is important.

Finally, Diesel #2 has a better fuel economy, so using it will cost less when compared to how many miles a truck can travel.

Diesel #1 might be used by semi-trucks in the winter, however, as it is more efficient in freezing temperatures. It is less likely to freeze in sub-zero climates and is easier on the engine as it has a faster starting period.

Diesel #1 is often called the winter fuel as it really shines in cold temperatures. If semi-trucks are traveling through very cold areas, they might switch the type of diesel they use.

Are semi-trucks good on “gas”?

Semi-trucks are not very fuel efficient. In fact, they only get about 6.5 miles per gallon, which is much different than cars, which can get an average of 24 miles per gallon.

The main reason for this lack of efficiency is that semi-trucks are so large. It takes a lot more fuel to carry massive weights.

When going uphill, semi-trucks can have a fuel efficiency as low as 3 miles per gallon. If you’ve ever driven behind a semi-truck while going up a hill, this won’t be a surprise.

In contrast, semi-trucks can reach an average of 23 miles per gallon while driving downhill. However, they need to be cautious as too much speed can lead to roll-overs and traffic accidents.

What’s the most fuel-efficient semi-truck?

As technology improves, there is a better awareness of how to create a more fuel-efficient engine for a semi-truck. While we might think that all semi-trucks are the same, there are different models with their own advantages.

Even though there is only a slight difference between the average miles per gallon that a semi-truck can achieve, every bit helps. These vehicles are constantly on the move and when you are traversing the country, a difference of 1 mile per gallon can result in thousands of dollars of savings.

The Freightliner Cascadia Evolution is a newer model with a Detroit DD15 engine. It boasts an average of 10 miles per gallon.

The Kenworth T680 Advantage is also a newer model with impressive fuel efficiency. It can get about 9 miles per gallon.

The Mack Pinnacle is all about traveling long distances and carrying heavy loads. It has a fuel efficiency of 8 miles per gallon.

How much does a semi-truck take in gas (fuel)?

The fuel tank(s) of a semi-truck have a capacity of between 125 and 300 gallons. Some longer-haul semi-trucks will have two gas tanks just in case a driver is traveling in a more remote area.

However, drivers will not completely fill their gas tank up as they need to leave some room for expansion and overfill. Instead, they will only fill up to 95% of their tank, just to be on the safe side.


Semi-trucks use diesel in their engines as they carry such heavy loads. Diesel engines are stronger and more durable, and thus will last longer.