What octane actually means
Octane isn't a measure of energy or quality. fueleconomy.gov defines it as "the measure of a fuel's ability to resist 'knocking' or 'pinging' during combustion." In the U.S., regular is usually 87, midgrade 88 to 90, and premium 91 to 94.
Engines with high compression or turbochargers squeeze the fuel and air harder, which makes knock more likely, so their makers call for higher octane. Most cars don't have that problem. fueleconomy.gov notes that most vehicles use 87 octane.
Required, recommended or regular?
Your owner's manual, and often a label inside the fuel door, says which of these three your car is. It changes the answer completely.
Premium required
Use premium. fueleconomy.gov says you should use the octane rating your manufacturer requires. Modern engines can adjust their spark timing to avoid knock on lower-octane fuel, but fueleconomy.gov says they still lose power and fuel economy when they do.
Premium recommended
This is the gray area. The engine is tuned to make its best power on premium but is built to run on regular. Consumer Reports found a "negligible performance difference when using regular fuel in a car for which premium was recommended." Check your manual for what it says about using regular, and use the calculator to see what the choice is worth in dollars.
Regular
Premium is wasted money for everyday driving. AAA's 2016 study found that "16.5 million U.S. drivers unnecessarily used premium-grade gasoline" at least once in a year, costing more than $2.1 billion, and its lab testing on regular-fuel cars "found no significant increases in any tested category" across horsepower, fuel economy and emissions. fueleconomy.gov notes one exception: during severe duty such as towing, higher octane may improve performance and gas mileage "by a few percent," though the extra cost usually outweighs it.
What premium costs: a worked example
- Gallons a year: 11,500 miles ÷ 22.2 MPG = 518.0 gallons
- Extra cost a year: 518.0 × an example $0.75 gap = $388.51
- Per month: $388.51 ÷ 12 = $32.38
- Per 14-gallon fill-up: 14 × $0.75 = $10.50
The 11,500 miles and 22.2 MPG are the EPA's figures for a typical passenger vehicle, the same defaults the gas budget calculator uses. If prices at the pump move, the gas price change calculator shows what any rise or drop does to your monthly bill.
If you want better gas, pick Top Tier, not higher octane
Some drivers buy premium because they think it's "cleaner." AAA's advice is that drivers who want a higher quality fuel "should save their money and select a TOP TIER™ gasoline, not a higher-octane one." Top Tier is a detergent standard, and it's sold in regular grade too. Consumer Reports also says Top Tier gas "is worth the investment" for keeping the engine clean.
What drivers are saying
- High prices have people asking the question. A MINI owners' group on Facebook has a post titled "With gas as high as it is, who has backed off of premium." We could only confirm the title, not the replies.
Most of what drivers argue about is whether premium helps a car built for regular. AAA's lab study says it doesn't, but it states it "did not evaluate the effects of using regular fuel in an engine that requires premium gasoline." That question is settled by your owner's manual, not by forum opinion. We couldn't read driver discussions in full for this page, so no replies are quoted.
Cedrick Reese put this page together because the premium question usually gets answered with opinions, when the cost side is simple math you can do with your own miles and the price gap at your station. The octane definitions and required-versus-recommended guidance come from the Department of Energy's fueleconomy.gov, the waste figures and lab results from AAA's published research, and the recommended-fuel finding from Consumer Reports. The only driver post cited is identified by its title, because the replies could not be read. The page is reviewed when those sources publish new testing, and the price gap shown is only an example.
Premium gas questions
Is premium gas worth it?
Only if your car requires it. fueleconomy.gov says to use the octane rating your manufacturer requires, and that cars built for regular get little to no benefit from premium in normal driving. AAA's lab tests found no significant gain in horsepower, fuel economy or emissions in regular-fuel cars.
Will putting 93 in an 87 car cause problems?
No, but it won't help either. AAA's testing of cars designed for regular found no significant increase in horsepower, fuel economy or emissions on premium. You'd be paying more per gallon for nothing in return.
Can I put regular gas in a car that recommends premium?
If premium is only recommended, check your owner's manual for what it says about using regular. Consumer Reports found a negligible performance difference when using regular in a car for which premium was recommended. If premium is required, use premium.
Is it okay to switch back and forth between regular and premium gas?
In a car built for regular, there's no reason to switch to premium at all, since AAA's tests found no benefit. In a premium-recommended car, follow what the owner's manual says about using regular. In a premium-required car, stay with premium.
Does premium gas clean your engine?
Not because of its octane. AAA advises drivers who want a higher quality fuel to choose a Top Tier gasoline rather than a higher-octane one. Top Tier is a detergent standard that is sold in regular grade too.
More fuel tools
See your whole fuel bill for the year with the gas budget calculator, or check what a price jump does to it with the gas price change calculator.
Premium is one of several ways drivers overspend on fuel. How to save money on gas puts a dollar figure on the rest.