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It’s a dilemma we’ve all faced: You pull up to the pump and can’t decide between premium or regular gas. For some, defaulting to the cheapest option may be standard. But for others who want to know if the lowest-priced option is truly best for their vehicle, the answer can seem a little hazy.
So, what is the difference between premium and regular gas. Let’s start with some gasoline basics and breakdown the variations between octanes. We’ll also address the questions between fuel choices and give you the information you need to know. Learn whether regular vs premium will help or hurt when it comes to vehicle performance, efficiency and longevity.
Aside from price, the key difference between premium and regular gas is octane rating—the measure of fuel’s stability. Broadly speaking, higher-level octane does a better job at resisting engine knock (i.e., the early combustion of the fuel-air mixture that causes your car’s cylinder pressure to spike, resulting in damage over time). In other words, the higher the octane, the lower the chance the fuel will detonate at the wrong time and harm your vehicle’s pistons and cylinder linings. But do you need higher octane gas? That answer all depends on the type of car you drive, and the requirements set by your vehicle’s manufacturer.
As a good rule of thumb, if your owner’s manual states that your car requires premium gasoline, you should use only premium. If your vehicle’s manufacturer recommends premium, however, use discretion; while regular gas may not harm your vehicle, it may deny you the performance and efficiency that premium gasoline would provide.
In the case of “recommended premium,” it may be worth it to do a little performance testing of your own. Start by getting your tank as close to empty as possible and fill up with premium gasoline. Track your gas mileage and make mental notes of your car’s performance for at least two tanks of premium fuel. Next, repeat these steps using regular gasoline and see if you notice any significant change. No change? No problem! You’re safe to use regular fuel and spend the extra savings elsewhere.
It's not uncommon to think of premium gas as a nice treat for a regular gas engine. But the truth is that premium gas doesn’t provide any extra power, fuel economy or acceleration over regular gas. If your engine runs well on regular gas, there’s no real benefit to spending more for premium fuel. Remain cautious about claims that premium fuel does more to clean deposits from your fuel injectors and various parts of the fuel system. The same detergent additives that are in premium fuel are also in regular.
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You’ve seen the numbers on the fuel pumps—87, 89, 91 and 93. What do these numbers mean? In most states, 87 octane is considered regular fuel, 89 is mid-grade and 91 and above would qualify as premium. In some places, 93 octane gasoline is referred to as “super-premium” or “ultra,” where 87 or 89 may be referred to as “silver” or “unleaded.” Try not to let these labels confuse you since they’re merely names given to octane ratings.
Unless your car requires premium gasoline or has a turbocharged engine, there’s really no harm in mixing regular and premium gasoline. In older vehicles, this kind of combination could’ve caused significant engine knock, but most modern engines are adaptable to variety. If your vehicle requires premium, however, and you mix regular gas into the tank, you could experience a noticeable decrease in power and fuel efficiency, if not a high repair bill later down the road.
You probably share the road with a fair number of diesel-powered vehicles each day, including semi-trucks, pickup trucks, busses and even passenger cars. These vehicles have engines that produce superior power and torque compared to the regular gasoline engines that are made for lighter cars and faster speeds.
Diesel and gasoline are both used in combustion engines, but the difference is in how each fuel ignites. Diesel engines have a compression-ignited injection system rather than the spark-ignited system used by gasoline cars. And unlike regular gas, diesel fuel is thick in density and slow to evaporate. Because of these unique operability qualities, you never want to use diesel to fuel a non-diesel engine. If a mistake is made, and diesel is added to a gasoline engine, the vehicle will stop running after a very short time. Will it ruin the engine? Probably not. But it’s likely to cost you a pretty penny in replacement parts. Unfortunately, if the reverse happens and regular fuel is added to a diesel engine, the results could be far worse. Diesel engines that accidentally take in regular fuel will need to be towed to a shop immediately where the gas tank can be professionally drained and cleared of contamination.
Ethanol is mixed in to more than 98% of U.S. based gasolines. This alternative fuel is made from various plant materials and is used as a cost-effective way to raise the octane rating of gas while meeting the requirements of the Renewable Fuel Standard.
You may occasionally notice non-ethanol gas available at some service stations. This clear gas has a longer shelf-life than ordinary gas and contains no corrosion reside. For this reason, many people choose to put non-ethanol gasoline in outdoor power equipment that may not get used daily (e.g., mowers, chainsaws, hedgers and leaf blowers). It’s less common to see ethanol-free gas used as the primary choice in cars, but there are times when fuel scarcity may make it necessary. Don’t panic if you must mix ethanol-free gas with regular gasoline in the short term. While frequent mixture can eventually contribute to corrosion, your car’s functionality will not be compromised in the short term.
All gasoline sold in the U.S. must meet a minimum level of fuel-system cleaning additives, as mandated by the EPA. But every fuel brand uses its own formula of more than 150 components, meaning that a car that runs well on one brand, might perform less efficiently on another. It’s up to the individual to do a little trial and error with their vehicle and note any differences in performance between brands.
For more gasoline facts and tips, visit AAA. And remember, AAA Members save at least 5¢ per gallon at Shell when signing up for the Fuel Rewards program (terms apply).
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