Note: Always fuel your car in keeping with the instructions in its manual to stay protected under the powertrain warranty.
Premium vs. regular gas
Back in the day, high-octane premium gasoline had more detergents in it than regular gas, so drivers would burn through a tank of premium once in a while to clean their engines.
The higher octane number on premium gas represents its ability to resist auto-ignition or “knocking,” which can damage car engines. But the quality difference between regular and premium is shrinking fast.
Newer emissions guidelines have forced refiners to introduce additives into all types of gasoline to reduce pollution and protect engines. At the same time, engine control systems are better at adjusting for low-octane fuels.
The difference between regular and premium gas
For cars that require premium gas, then using a lower-octane fuel might cause engine knocking. But in practice, modern cars have a knock sensor in the engine’s control unit that helps prevent damage from happening.
If premium is merely recommended for your model, the manufacturer may say you'll see “decreased performance” when using regular. But this may not be noticeable.
Consumer Reports tested this out on the Acura TLX and Nissan Maxima V6, two cars that recommend premium gas.
CR found they accelerated from 0 to 60 mph in the same amount of time using regular or premium — and there was no engine pinging or knocking in either car when it ran on regular fuel.
In short, unless the carmaker requires it or you're driving a race car, you probably don't need premium gas.
Is premium gas better?
Even when premium isn't required or recommended, some motorists choose the most expensive fuel — maybe because they think they're giving their car a special treat.
But engines don’t always make the most efficient use of premium gasoline.
In a study, auto club AAA found that cars that don't ask for premium do see a benefit from the higher-octane fuel, but only when they're driven long distances at high speeds, or if they're hauling heavy cargo or towing.
If you hear an unusual knocking or clunking sound from your engine while doing one of these activities, it could be a sign your car is thirsty for premium. Otherwise, you're probably just wasting your money.