Marine Fuel Vs Auto Fuel

You just got a used boat with a two-stroke motor. This boat is your very first experience with watercraft. You learned in boating school that marine fuel is the only kind you should use. While others prefer regular or auto fuel, some only use Premium. 

So, marine fuel vs auto fuel- which one is the best? 

Fuel used on ships typically does not include Ethanol but auto fuel has. The octanes of marine fuel are comparable to those of auto fuel. Also, marine fuel is much more expensive than auto fuel. The viscosity grade of marine fuel is also higher than that of auto fuel.

Further nuance is invested in the two fuels. Everything you need to know is in this article.

Marine Fuel Vs Auto Fuel

General Overview

The table below compares marine fuel to automobile fuel and lays out the key differences between the two-

FeaturesMarine FuelAuto Fuel
BaseHydrocarbon, API gravity, Sulphur contentEthanol, Petroleum
Viscosity gradeHigherComparatively lower
Octane rate HigherLower

In-depth Comparison

Let’s compare the two types of fuel head-to-head now that we have all the facts.


Marine fuel is thought to have formed from sea plants and animals over millions of years. After passing away, they sank to the seafloor, where they were covered by sand and mud to form an organic-rich layer. 

These layers accumulated over time, until they were several tens of meters in height. Dust and slime solidified into sedimentary rock, while decomposing matter congealed into oil and gas droplets. 

Gas and oil moved through the porous rock, eventually becoming trapped by an impermeable layer of rock. And accumulating at the highest point.

Various hydrocarbons and trace amounts of impurities make up crude oil. According to its origin, crude oil’s chemical makeup can be very different. 

Fuels that aren’t refined from the same region can vary greatly. Because of the variations in the petroleum format in layers.

Auto fuel systems must safely deliver combustible liquids from the water reservoir to the engine and back. Elastomeric parts such as O-rings, eyelets, valves, tubing and ducting, tank parts, filling systems, and the fuel pump are all present. 

Automobile fuel system compounds must have good sealing and fuel resistance.

Mainly ethanol is the foundation for this biofuel blend.

While regular gasoline may contain up to 10% ethanol, marine gas typically does not. To put it another way, the octane rating of marine gas is 90. (can be said mid-grade auto fuel). 

It’s worth noting that the additive bundles aren’t exactly the same (auto fuel has more cleaners). 

In a comparison of marine fuel to auto fuel, we found that marine fuel contains far fewer of the latter’s common ingredients.

However, there is no harm in using auto fuel in your boat occasionally or marine fuel in your car. If you don’t take your boat out very often, you might see a big change.


Big ships and commercial vessels use fuels like IFO, HFO, MGO, as well as MDO (Marine diesel oil). The densest commercial fuel refined from crude oil is denser than both gasoline and naphtha.


If auto gas sits on the water between uses, the ethanol in the gas can separate from the ethanol. The seals can deteriorate faster. 

Unlike regular gasoline, marine gas is not subject to sales tax. Its price is comparable to that of auto fuel. Being that marine gas can only be accessed by water.

So it lacks a competitive market. It allows the price to be set (typically higher) to take advantage of the captive audience.

Filling up at a gas station, rather than marine fuel, can save you anywhere from $0.2 to $0.5 per litre of fuel for a small boat. 

You can save money on boat fuel by getting it from a filling station instead of the marina. Moreover, unlike large vessels, boats can run on regular auto fuel.

Viscosity Grade

At 50 degrees Celsius (122 degrees Fahrenheit), the viscosity of marine fuels varies from below one centistoke) to around 700CSTt (1 CST = 1 mm2/s). 

Furthermore, higher viscosity grades require preheating during operation. It reduces their viscosity to a fuel injection-acceptable range (8 to 27 CST).

Alternatively, marine fuel has a higher viscosity grade than auto fuel. Due to the thinner consistency of auto fuel compared to marine fuel. Sometimes your boat may not go neutral because of the viscosity grade of the fuel.


The ease with which engine oil began pouring at a given temperature is referred to as the oil’s viscosity. At low temperatures, thinner oils are easier to pour than their thicker counterparts because of their lower viscosity. 

Engines benefit from thinner oils in cold weather because the reduced friction makes them easier to start. So, we can declare auto fuel as the winner. Because the boat submerges into the water and the temperature tends to lower there.

Octane Rate

In the United States of America, the octane rating of the fuel used in most boat engines must be at least 87.   However, if you use fuel that contains ethanol and don’t have a fuel gimbal or water spacer filter. 

Upgrade to premium fuel with a rating of 90 or higher if you are boating 2-3 foot waves. Here the octane rate of marine fuel is a bit higher than that of auto fuel. 



The winner is crystal clear: marine fuel. Because regular gasoline contains ethanol, marine fuel either doesn’t contain any or contains much less.

Which One to Go for

Both are wonderful choices; you won’t go wrong with either.

Fuel used on ships typically does not include Ethanol. Watered-down fuel is the result of ethanol’s ability to absorb atmospheric moisture. 

This is a horrible thing if you happen to be sailing the ocean solo. The octanes of marine fuel are comparable to those of auto fuel. 

In order to prevent cylinder detonation at higher engine compression ratios, higher octane fuels must be used. This also occurs in turbo-aspirated, high-compression ratio, sea-level automobile engines.

It’s important to have adequate insurance coverage in case of water contamination. It comes with its own set of costs, as does adequate water storage facilities. 

Costs associated with installing and maintaining space and pumping systems for marine use are higher. If you want to save money, you can use regular automobile gas in your boat’s motor.


Is there a variant of marine fuel used on boats?

As with your car, it requires fueling. Gasoline grades from unleaded (87 octanes) to premium (93 octanes) and diesel can all be used in private boats.

In what way does marine fuel differ from other fuels?

Bunker fuel is used to power the motors on ships, but it may not be standard white diesel. It’s true that diesel is used as bunker fuel by some ships. While marine gas oil (also known as LSFO, or low sulfur fuel oil) is used by larger vessels.

May I fill my boat with regular gas?

Your boat’s engines can run on regular gasoline, but they must be either E10 or ethanol-free. Using E15 or regular gas with a higher ethanol content is discouraged.


We now have a much better understanding of marine fuel vs auto fuel. Though marine fuel is a bit expensive, both boats are top-notch, so either choice is fine.

If you read our article, you should be able to find the perfect boat for your needs. Keep in mind why you want to use the boat in making your choice.

Wishing you the best of luck!

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