It seems to be the simple question to ask, but sometimes it is difficult to understand what all these words and numbers mean.
Most gas stations in the US offers at least 3 types of gas: Regular, Middle and Premium. The other things may help you understand the concept of choosing gasoline is octane number.
How octane number refer to type of fuel
Regular fuel refers to 87 octane number, Mid-range is frequently a 89, and premium/top range is 91 or 93.
What is difference between octane numbers
Generally, the higher octane rating the more it resistant to pre-ignition. This resistance required when your car’s engine has high air compression ratio – it primary refers to premium or sport cars.
If you use a higher octane number than prescribed by owner manual in your car – it’s more likely a waste of money. If you use lower octane number gasoline – it may cause harm consequences.
Car requirement interpretation
If your car owner manual recommends 87-89 or Regular – you are lucky, so you could use cheaper fuel without any consequences.
In case your car manual or gas cap label claim premium fuel required – it means that you must use only premium fuel. Using regular or mid instead – leads to possible engine damage and low fuel economy.
You find phrase premium fuel recommended – it means that you could use mid-range fuel without any harm to your car, but with higher fuel consumption.
For EU-spec cars
Cars imported from Europe has different ratings – 95 or 98 RON. It is equivalent to Mid-Premium, or 91 octane number for 95 RON and 93 octane number to 98 RON.
What means E85
E85 is a special gasoline made mostly of ethanol (85% ethanol 15% gasoline), it also known as flex fuel.
Ethanol is bio-fuel derivative from corn; it is less expensive and less harm for environment. However, E85 usage leads to higher fuel consumption. You could also use Regular gasoline instead.
For diesel car owners there is no such diversity. Most gas stations in US and Canada has only one grade of diesel fuel – ULSD which stands for Ultra Low Sulfer Diesel.
However, there are E85-like variant for diesel and it’s called BD5 or BD20. The number after letters shows the percentage of methanol. Most of new cars are limited to 5% ethanol diesel.