When you fill your car up, you have options. There are several different fuel grades to pick from, and you usually just pick the cheapest one. But what do all of those numbers mean? And what’s the difference between the cheapest and most expensive options? Read on to learn about octane ratings, the difference between unleaded and premium, and how to decide which fuel is best for your vehicle!

FUEL GRADES EXPLAINED

In the United States, unleaded fuel grades are defined by the “octane” rating. The octane rating, the number on the yellow sticker on the gas pump, is listed as the anti-knock index (AKI). The AKI is a measurement of how well the fuel resists detonation.

Your engine compresses fuel to a high degree, which can sometimes cause it to ignite – instead of how it’s intended to, by a spark from the spark plug. This causes what’s known as an engine knock. Engine knock can damage your engine, so this information is important! The higher the octane, the higher the AKI, and the better the fuel resists detonating too early.

WHAT ARE THE DIFFERENT FUEL GRADES?

Fuel grades can depend on where you’re filling up and the local regulations. At almost every gas station, fuel grades will include regular, mid-grade, and premium. The only difference is that, depending on the location, those gas station fuel grades will have different octane ratings.

  • Regular gas is the lowest octane level. In most places, this is 87 octane.
  • Mid-grade gas is usually an octane level of 89.
  • Premium gas has the highest octane, often 91-93.

MAY CONTAIN UP TO 10% ETHANOL

Now that you’ve identified the yellow octane sticker, you’ll most likely see another sticker that reads “May Contain Up to 10% Ethanol”. Ethanol is a renewable fuel made from various plant materials collectively known as biomass.

More than 98% of U.S. gasoline contains ethanol to oxygenate the fuel. Because of its high octane rating (between 109 and 113), ethanol can boost gasoline’s octane with as little as 10% added to it.

FLEX FUELS AND A NEW BLEND

While the pumps at a majority of the gas stations around the country will have either regular, midgrade, or premium fuel, some offer Flex Fuel, also known as E85. This specific blend of gas and ethanol can consist of up to 85% ethanol and as little as 15% gasoline. E85 is intended for flex-fuel vehicles only, which often have a yellow fuel cap to remind owners of the dangers of using regular gasoline in that model.

A relatively new fuel marketed as Unleaded 88 is 88 octane but contains 15% ethanol instead of the standard 10%. All gasoline and flex-fuel vehicles can use E15, but Federal law prohibits its use in older vehicles, boats, or power equipment because of the damage it may cause.

WHEN TO USE DIFFERENT FUEL GRADES

REGULAR UNLEADED

It’s worth noting that in some high-altitude states, such as Colorado, regular can be as low as 85. In places where the air is less dense, the octane can be lower and still produce the same level of performance in older naturally aspirated vehicles. Most modern cars, however, do not have carburetors and do not perform well with gas this low octane.

For everywhere else, 87 is usually “regular” gasoline. Regular is suitable for most standard vehicles and is available almost everywhere. Regular is the cheapest and the most commonly used for daily drivers.

MID-GRADE

Called “plus” by some gas brands, mid-grade is usually 89 octane. This grade is used in vehicles that require a slightly higher octane rating but not premium. Keep reading to learn about cars that require premium fuel – and how to tell which is best for your vehicle!

PREMIUM UNLEADED

Premium is typically 91-93 octane, depending on your location. Premium is designed for higher-performance vehicles or those with high compression ratios. Many manufacturers of high-performance cars require the use of premium-only fuel to honor their manufacturer’s warranty. Consult your vehicle’s manual to determine if you need to use premium or if regular and mid-grade will work fine. If you’re looking for a premium gasoline without ethanol, look specifically for 91 octane with the sticker reading “contains no ethanol”.

FLEX FUELS

Again, make sure your vehicle is intended to run on Flex Fuel before adding it to your tank.

CAN YOU MIX GAS GRADES?

When you went to fill up last week, the station was out of everything except premium – oops! Now you’re down to half a tank, and your wallet is begging you to top off with regular.

Can you switch gas grades? Yes! Switching from premium to regular is safe if your owner’s manual does not indicate that your vehicle requires premium fuel.

Mixing gas grades is fine, but if your vehicle is built explicitly for premium fuel, you could experience performance issues or damaging engine knock if you use a lower octane fuel.

WHAT ABOUT FUEL TYPES?

Note that you cannot switch between fuel types – in other words, a gasoline vehicle cannot take diesel, and vice versa! Accidentally fueling your vehicle with the wrong type, not grade, of fuel can result in catastrophic damage to your engine.

If you realize you’ve accidentally used the wrong fuel type and are still at the pump, do not start your engine and call a tow truck to bring your vehicle to a repair shop. If you start your car, the fuel could enter your engine and ruin it permanently. If you’ve already started your vehicle, come to a safe stop immediately, turn it off, and then have your car towed.

TURN TO VENTURE FUELS FOR ALL OF YOUR COMMERCIAL FUEL NEEDS

No two fuel grades are the same, just like no two fuel suppliers are the same. When you need a quality fuel supplier you can depend on, turn to Venture Fuels. Contact us to learn about how we can meet your commercial fuel needs.