Unleaded vs. premium gas: What’s the difference?
With the exception of diesel fuel, all gasoline sold at gas stations is some form of unleaded gas. The different unleaded fuel options you see at a gas station include regular, midgrade, and premium gas, all of which have different octane levels.
Octane levels explained
The octane rating of different fuel types measures fuel stability, and fuel grades with higher octane ratings have greater fuel stability. Both spontaneous and controlled explosions occur in an engine. However, spontaneous combustion creates pressure that can disrupt and damage engines. Octane ratings measure the fuel’s ability to resist or reduce this spontaneous combustion damage, which is often referred to as “engine knocking.” Although newer-model cars have features to prevent engine knocking, higher octane fuel may also improve engine performance, fuel efficiency, and reduce CO2 emissions.
When selecting fuel options at a gas station, you’ll generally see three separate numbers between 87 and 94 listed on the pumps. This number refers to the octane rating of the gasoline. All three of these options are unleaded gasoline, though each falls into one of the following specific categories:
Regular: The lowest octane fuel that’s generally labeled as 87
Midgrade: The middle range of octane fuel that’s generally labeled as 89 or 90
Premium: The highest range of octane fuel that’s generally labeled between 91 and 94
You may also see a pump labeled with the number 88, so you should know how unleaded 88 differs from unleaded 87 and 89. Unleaded 88 simply contains more ethanol than unleaded 87 gasoline. Unleaded 87 typically has 10% ethanol, while unleaded 88 has 15% ethanol. Unleaded 88 can be used in many modern vehicles, but it shouldn’t be used elsewhere.
Which gas should you choose for your engine?
All vehicle manufacturers either recommend or require the use of an unleaded gasoline with a specific octane level. Most manufacturers list this information in the owner’s manual. Many vehicle engines are designed to run on regular gasoline, but some manufacturers recommend midgrade or premium gasoline. Choosing the correct gas for your vehicle helps your engine run optimally.
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