When you pull up to a gas pump or see a sign for a gas station advertising its prices, it is impossible not to notice that there are usually three different gasoline grades for sale, each at a different cost per gallon. Typically you will see these different gasoline grades called Regular, Plus, and Premium or Super. These are not just clever names used for marketing purposes. While they might sound like more appropriate names for sandwich or pizza sizes rather than fuel types, there are a couple of distinctions among them that result in the different prices per gallon you see.
Premium Gas vs Regular Gas
So what is the difference between the various gasoline grades besides cost per gallon? The most obvious difference is the octane rating. The octane rating is a number which represents the level of octane in the gasoline you are buying. For example, at your local gas station you might see the number 93 on a sticker near the nozzle that dispenses Premium while the Regular product might display an octane rating of 87.
Premium Gas vs Regular Gas - Premium has a Higher Octane Rating
The Octane Rating
The octane rating also reflects the relative amount of protection offered against engine knock. Engine knock results when the unburned air and fuel mixture does not burn cleanly and detonates instead. This causes a distinct, metallic pinging sound that comes from underneath your hood. You may have heard it before or you might be all too familiar with.
Gasoline Grades, Premium Gas and Engine Knock
One possible cause of engine knock is filling up with gas that has a lower octane rating than your car manufacturer recommends. While premium gas can sometimes be a solution for engine knock, that does not necessarily mean that the premium gas vs regular gas decision is settled. Most modern engines have sensors that detect knocking and adjust the timing of the spark on the fly to eliminate engine knocking. Engine knocking can also mean defective knock sensors, improper engine timing, or faulty oxygen sensors. So premium fuel might not solve your problem if you are hearing engine knock, but it can be worth a try.
Another Difference Between Premium Gas and Regular
One additional difference between premium and regular gas is the amount of detergent used as an additive. In 1995, the US Environmental Protection Agency established a standard for detergent in gasoline. So all grades of gasoline now contain some amount of detergent.
These detergents can help to keep your engine clean and more fuel efficient by reducing carbon deposits. Detergents can reduce emissions to help protect the environment as well. Premium gas often contains significantly higher levels of detergent additives than Regular. Some companies even advertise that their high octane gas contains more detergent than the EPA requires which is certainly true. For example, according to one recent study, the Regular offering from Shell with an octane rating of 87 contained 16.2 milligrams of detergent per 100 milliliters while their Premium gasoline contained 31 milligrams.
Sounds almost good enough to pay an extra 20 cents per gallon, but does the higher concentration of detergent in premium gasoline result in a significant performance improvement or less buildup? The US Federal Trade Commission does not think so. In one of the consumer notices you can find on the FTC website here, in response to the question of whether higher octane gasoline will clean your engine better or not, the FTC in part that as a rule high octane gasoline does not perform better than regular octane in preventing deposits, removing deposits, or in cleaning the engine.
Which Grade of Gasoline Should I Buy?
If you are not sure which gasoline grade is best for your car or if you have been buying one or the other without giving it much thought, you should check your car owner’s manual. The owner’s manual will have a recommended octane level. The simple answer is that if your manual recommends Premium, use Premium. If Regular is recommended, use Regular.
Most modern cars are designed to run on Regular gasoline, but depending on the make and model of your vehicle, your car maker may recommend gas with a higher octane level than you will usually find in Regular. Luxury cars and high performance sports cars for example may recommend filling your tank with nothing but Premium gas.
If your manual does recommend Regular, in certain specific circumstances you still may want to fill up with Premium instead. Understand that the suggestion here is not that you ignore your manual, but if your engine is knocking or pinging despite your using gasoline with the car maker’s suggested octane level then you might want to try switching up to the next highest grade to eliminate the engine knock. If the knocking persists after you make the change, an engine tune up or other repair may be required. Once you have your engine serviced, you can switch back to Regular or mid-grade, whichever is the lowest grade that your engine will run on without knocking or pinging.
If your car is newer or has been well maintained and you are not experiencing any performance problems or engine knock, there is nothing wrong with sticking to Regular if that is what your owner’s manual recommends. Premium should not be taken to mean better. It is highly likely you will receive any benefit or value from spending extra on Premium when your car manufacturer recommends Regular.
