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If you’ve ever found yourself standing at a gas pump, trying to decide between 87- and 93-octane fuels, you’re not alone. The world is full of people wondering why their seemingly average cars require premium fuel. On the flipside, there are just as many folks wanting to know if premium fuel would pump up the performance of their sagging econo-box’s engine.

Car Bibles’ editors have made nearly every mistake in the book when it comes to fuels and octane ratings, and we’re here to help you avoid the same trouble. In many cases, the worst that will happen is that you’ll end up wasting a few bucks at the pump, but there can be some real consequences to using the wrong types of fuel over extended periods of time.

Let’s get rolling.

Octane in fuel can be affected by the crude oil it came from.

Octane Is the Name of the Game

Octane measures the level of compression that fuel can handle before igniting. Higher-octane fuels are less likely to ignite at the wrong times, sometimes called pre-ignition or engine knock, which can damage engine internals. Higher-octane fuels are good for high-compression, high-powered engines.

What Makes Regular Fuel Regular?

Regular gasoline is a byproduct of crude oil and may contain up to 10-percent ethanol. Where premium fuels carry octane ratings of 90 or above, in most cases, regular fuels are generally in the 87- to 90-octane range. At the pump, you will usually see regular and mid-grade versions of the fuel, each with a different octane rating. Not many vehicles require mid-grade gas; they can be run on less-expensive regular fuel. If you notice engine knock with regular gas, however, an upgrade might be the solution — but not always.

What Is Premium Gas, and Why Is It More Expensive?

Depending on the type of crude being refined, premium fuel can contain alkylate or other octane-boosting chemicals. Premium gas carries a higher octane rating than regular gas. In most premium gas blends, the octane rating is somewhere between 90 and 94 octane. Premium fuels were designed to help engines resist knock, which can make the engine wear more quickly than it should if repeatedly encountered over an extended period of time. 

Newer vehicles’ computers are designed to sense and prevent knock by changing timing, but many manufacturers still recommend premium fuels, especially for high-performance and turbocharged engines. Its higher octane rating, combined with the fact that it’s typically more expensive to produce, makes premium fuel more expensive.

Why Has the Gap in Price between Gas Grades Changed in Recent Years?

To better understand how gas prices are determined, we spoke with Patrick De Haan, head of petroleum analysis at Gas Buddy. De Haan explains that, up until about 10 years ago, the price gap between grades of fuel was usually about 10 cents. So, the gap from regular to mid-grade was a dime, and the gap between regular and premium was about 20 cents. That’s no longer true. In many cases, gas with a higher octane rating is significantly more expensive. De Haan attributes the growing price gap to a shift in the types of crude oil that were coming to market in the early 2010s. He says that crude from Canadian oil became more prevalent and many refineries across the United States shifted to work with the product. The crude oil coming from Canada is what is known as heavy sour, which De Haan says tends to yield a lower octane rating when compared to light sweet crude from other regions. 

The refineries’ adoption of heavy sour crude meant that the input materials were cheaper, so their use became more common. De Haan says the current discount for heavy sour crude over light sweet crude is around $13 per barrel. If you can imagine a refinery that runs through hundreds of thousands of barrels each day, that discount adds up to a significant sum. The problem, he explains, is that the use of the less expensive, low-octane-yield crude led to a sort of octane shortage in the gas market. Alkylate, which is a chemical used to boost octane in gasoline, became a high-demand product, driving the price higher by a considerable amount. This, in turn, drove prices of premium fuels higher. 

The good news, if there is any, is that refineries in some areas of the country still import and run light sweet crude oil, so it’s still possible to find premium fuels for 20 cents or more than regular. This is true in states such as California, but that doesn’t mean the overall price of gas is more affordable in those areas. (It’s usually not.) 

Most gas stations offer at least three octane ratings.

What Happens if I Use Regular Fuel in a Vehicle that Requires Premium?

Years ago, running lower-octane fuel in a vehicle that requires premium could result in engine knock, but the times and technologies have changed. Today, vehicles that require premium fuel are generally able to adjust the engine’s timing and performance to accommodate the reduction in octane. This is OK when you’re at a gas station that doesn’t have premium available, but regular shouldn’t be your go-to fuel if your vehicle’s manufacturer recommends otherwise. You could end up voiding the warranty if damage occurs, so be sure to understand your vehicle’s requirements. 

What’s the Relationship Between Premium Gas and Turbocharged Engines? 

Not all turbocharged vehicles require premium fuel, but in most cases they will run best with it. This is because the turbo increases engine compression and may cause lower-octane fuels to pre-ignite. Many newer vehicles have sensors and onboard software that can alter engine operation to accommodate lower octane fuels, but their best performance is only available when using premium.

Car Bible’s Glossary for Premium Gas

Welcome to Bibles school! 

Engine Knock

Knock refers to combustion of the air-fuel mixture that ignites and burns unevenly and at the wrong times. The mixture should only be ignited by the spark plug at a specific time, and knocking occurs when the ignition takes place when it’s not supposed to. 

Diesel Fuel

Diesel fuel is designed for diesel engines and is less volatile than gasoline. Diesel engines do not ignite fuel with a spark. Instead, they use a combination of extreme pressure and high heat to burn the fuel. Diesel fuels generally release more energy when burned than gas, giving diesel engines better fuel efficiency. 

Race Gas

Race gas takes high-octane fuels to another level through the use of additives that increase the 93-or-higher octane rating even more. Ethanol and methanol are examples of those additives. 

Biofuels

Biofuels are fuels made from an organic material, which can include plant matter. They are typically blended with gasoline or related fuels but can sometimes be used alone. 

The Car Bibles Questionnaire

Q: Do all premium and luxury cars require premium fuel?

A: There was a time when high-performance engines in many luxury vehicles required premium fuels, but today’s automotive market is much different. In recent years, the growing popularity of hybrids and more fuel-efficient powertrains has meant that several models run just fine on regular gas. 

Q: Can I mix regular and premium fuels?

A: You can, but there is no tangible benefit to doing so. Mixing regular and premium gas will yield an octane rating somewhere between the two, depending on the amount of each. 

Q: Can I use premium fuel in a car that does not require it?

A: Of course, but running premium gas in an economy car with a buzzy four-banger engine isn’t the best use of your money. Follow the manufacturer’s guidelines here, and you’ll be just fine.

Q: Which Cars Require Premium Gas?

A: Several “everyday” vehicles come with a manufacturer’s recommendation for premium fuels. A few examples include:

  • Volkswagen Arteon
  • Honda Civic (models with a 1.5-liter turbo engine)
  • BMW i3 (with gas-powered range extender)
  • Polestar 1
  • Mercedes-Benz S560e
  • Audi A4

Video on Premium Fuels

If you’re confused about what to buy to improve your vehicle’s fuel-system performance, you’re not alone. Car Bibles’ editors have grabbed a few of their favorite products to get your project started right. They include STP Octane Booster, Gumout High Mileage Fuel Injector Cleaner, and Mechanix Gloves.

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