What's the difference between types of gasoline?

A guide to different types of gas

September 6th, 2016 by

What's the difference between types of gasoline?

You've seen it every time you visit the a gas station for a fill-up: Each fueling station has at least two different types of gas, if not more. But what are the differences between regular, mid-grade premium and diesel gas? Is one kind of gas better than the others? The following is a guide to the different types of gasoline available:

Regular is the most commonly used form of gasoline and typically the least expensive per gallon outside of diesel, which we will discuss shortly. Gasoline – sometimes called "petrol" – is a fossil fuel derived from oil, made up of hydrocarbons (mainly paraffins, naphthenes and olefins). Various additives are brought into the mix to help keep engines clean and improve combustion, including ethanol, a form of alcohol.

Ethanol raises the combustion point of gasoline, making cars perform better and boosting a car's "octane" rating. Higher octane roughly translates to better performance, though modern engines can offer high performance even with lower octane rated gasoline. Regular unleaded fuel typically comes in at an octane rating of around 87. This is, considering its low price and recent improvements in formula, what has made regular unleaded fuel the gold standard for the majority of motorists.

"I myself feel that the auto industry has evolved to a point where regular octane fuel is fine, due to better quality and integrity of the fuel systems today," Bill Griffin, owner of Griffin's Neighborhood Auto Clinic, told Angie's List. "I only run regular fuel and never have had an issue."

Mid-grade and Premium
Both mid-grade and premium fuel options offer higher octane levels – about 89 for mid-grade and 91 to 93 for premium. While some claim this leads to higher performance, some experts like Griffin are not so sure the boost in price from regular is justified.

"Premium is, yes, a few octane points higher, which provides a more efficient burn in the combustion chamber," Griffin said. "But it is a choice. Slightly better fuel economy is there, but it's not worth the huge price gap from regular to premium."

Premium gas can be significantly more expensive than regular, upwards of 10 to 15 percent more per gallon. While luxury brand cars often advise a higher-grade gas, most experts agree with Griffin that modern engines are designed to work nearly as well with regular gas.

"Today, engine control systems can compensate for low octane by monitoring knock activity and adjusting ignition advance to avoid knocking," Phillip Reed, a senior consumer advice editor for Edmunds.com, wrote on the site. "This sophisticated electronic capability effectively tunes the engine on the fly and gives drivers more flexibility in the grade of fuels that they can safely use."

Diesel fuel is a whole different story. Diesel is a distillate fuel, made from distilling crude oil, and is used exclusively in engines made to handle the fuel. Diesel has a much higher boiling point than commercial gasoline, meaning that if you put diesel fuel in a normal car engine (or visa versa) it could cause catastrophic engine failure and serious damage – not least of which would be a car shooting out thick, acrid exhaust similar to commercial trucks. 

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