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What Are the Grades of Gasoline? The Differences Between Premium Gas & Regular Gas

Young woman refueling car at self service gas station

Most retail gasoline stations in the United States these days have a choice of three types of gasoline available today for those of us who drive a regular auto or pickup or a high performance vehicle. Depending on what you drive, you have a choice between:

  • Regular Gas (the lowest octane fuel – generally 87)
  • Midgrade Gas (the middle range octane fuel – generally 89-90)
  • Premium Gas (the highest octane fuel – generally 91-94)

Some stations have different words for these grades of unleaded gasoline, such as unleaded, super, or super-premium, but they all refer to the octane rating. It all boils down to the fuel-air mixture that causes spontaneous combustion and starts your auto.

Owners of diesel fuel vehicles generally know they need to choose that selection, but what about the rest of us? What’s better?

How do you know which kind to use? People want their car to last as long as possible but want to save as much money and get the best fuel economy as they can, too. Also, using the wrong type of gas could also affect your auto insurance coverage in case of an accident. To understand the main differences and how they affect modern engines, the following information about grades may clear things up.

Different Grades of Fuel

If you’ve ever pumped gas, you’ve seen the big yellow square on the gas pump with large numbers on it. That yellow sticker is a label with information showing that pump’s minimum octane rating — but what does that mean?

Scientifically speaking, it’s a hydrocarbon derived from processing petroleum. However, in terms of fuel, an octane rating measures a fuel’s ability to resist “knocking” or “pinging” during combustion, caused by the fuel-air mixture detonating prematurely in the engine.

The “(R+M)/2 Method” on the label refers to the testing method used, where R is Research Octane Number (RON) and M is Motor Octane Number (MON).

What is RON and MON and How Does it Affect the Grade of Gasoline?

The RON rating falls somewhere between around 91 and up to 100. An average RON of 95 generally provides you with better fuel economy than a RON of 91. It simply means the higher the RON the more resistance to burn, which provides a higher level of mechanical energy, engine power and fuel efficiency to your engine.

Keep in mind that unless you have an engine designed to take advantage of a high RON (anything above 95) you won’t see a huge difference in performance and mileage.

Drivers won’t see the MON number at the service station. The number describes how fuel behaves in your engine at high temperature and higher engine speeds. The MON number is somewhere between 85.0 and 88.0, depending on the grade.

In the United States, an average of RON and MON, called the anti-knock unit, is used. In Europe, the RON alone is used. The United States considers 93 to be premium gas, while in the UK, premium is 98.

Gas pumps showing grades of gasoline and octane ratings

Which Grade of Gasoline Should I Use?

It’s a good idea to use the octane rating required for your vehicle by the car manufacturer. You can find that information in your vehicle owner’s manual. Most vehicles that run on gasoline, as opposed to diesel fuel, are designed to run on 87 octane (regular or unleaded), but others use higher octane fuel (like midgrade gas or premium gas).

Specific cars, such as high-compression engines in high performance vehicles, need at least a rating of 91. Owners of diesel engines and some specific models may find they run best on this level. Most automobiles run on lower octane fuel just fine.

How Does Each Grade Affect My Car?

Using a grade of gasoline that is too low for your car can damage the engine and emissions control system over time and your fuel efficiency will suffer. Using the right chemical mixture will help you get better gas mileage and provide other benefits.

Repetitive tapping or a pinging sound from your engine that becomes louder and faster as you accelerate is a classic sign of engine knock. This usually happens in older vehicles, while many newer vehicles can adjust the spark plug timing to reduce knock. Either way, knocking is an indication that the engine may be running poorly due to using the wrong grade of gasoline. You can try filling up with a few tanks of a higher grade to see if that eliminates the issue.

Using a higher octane fuel than your car requires may improve performance and gas mileage on some cars. It could also reduce carbon dioxide (CO2) emissions from your tank by a few percentage points during heavy-duty operations (e.g., towing a trailer or carrying heavy loads), especially in hot weather. However, under average driving conditions, drivers are likely to get little to no benefit. Therefore, it’s rarely worth the extra cost at the pump.

What About Other Types of Fuel?

You may see even more options at certain gas stations when looking at the pump. One of those is usually the addition of ethanol. It has a much higher octane rating (about 109) than gasoline and is usually blended with gasoline to help boost its octane rating. In fact, most gasoline in the U.S. contains up to 10% ethanol, but some stations offer blends of up to 15%. Most vehicle manufacturers approve this ethanol blend in recent-model vehicles, but it’s up to you to decide if you want to spend the extra few cents per gallon or not.

In areas with high elevation, gasoline with  the lowest octane rating of 85 may be available. In these areas, the barometric pressure is lower, so most older carbureted engines tolerate it fairly well, and it is cheaper – an extra advantage. Generally, it is not advised to use this grade for newer vehicles and even some older ones.

What is the Best for 2-Stroke Engines?

Most 4-stroke engines don’t need a mixture of gas and oil and, in fact, may have their power output harmed by the combination. However, a 2-stroke engine does use an oil and gas combo for its fuel mixture. Be sure and use only two-cycle oil, since regular motor oil will mess up your spark plugs. If you have questions, always refer to the vehicle owner’s manual since a particular manufacturer might recommend something different.

Each 2-stroke engine will need specific treatment to mix properly. Common uses include weed whackers, ATVs and some motorcycles.

Should I Use a Detergent Additive?

Unlike your laundry, a detergent additive in your tank (whether gasoline or diesel) prevents harmful deposits in your engine combustion system. The EPA has established standards for the minimum amount today’s gasoline can contain and those standards are much lower than before due to harmful emissions. However, you can add these chemical compounds if you want.

Detergent gasoline helps prevent the loss of power, fuel economy, poor idling and higher emissions that come from a dirty combustion system. Many specific car manufacturers, such as General Motors and BMW, recommend using it for peak performance.

Find Affordable Auto Insurance Online Today

Whether you use regular gas or premium  gas in your tank, you can be sure you’re getting the best grade on car insurance with a free car insurance quote online from Freeway Insurance. You can also call (800) 777-5620 today to speak to a live agent.

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