You pull up to a gas pump and you’re confronted with a dilemma: do you pay out for the premium gas or opt for the cheaper regular gas? Is this just a clever gimmick or is premium gas worth those extra dollars?

What is premium gas? And how is it different from regular gas?

Whether gas is considered premium or not boils down to octane levels found in the fuel. The higher the octane rating, the more resistant the gas is to knock. Knocking occurs when fuel burns unevenly in your engine's cylinders. As opposed to the air-fuel mixture burning smoothly in uniform bursts within the cylinder, odd pockets of the air-fuel mixture can burn up in uneven pockets creating mistimed bursts. This will create an unusual pinging sound and can cause damage to your engine's cylinder walls and pistons.  

At most retail gasoline stations, three octane grades are offered: 87 (regular), 89 (mid-grade), and 91-93 (premium). However, this can vary internationally and even from state to state. As the names suggest, you’re going to pay more money for premium compared to regular.

Can you put premium gas in any car?

It should be clearly stated in your vehicles’ manual whether to use premium gas or not. Some cars will also feature this information in the casing around the fuel cap just as a gentle reminder before you fill up the tank.

You should always follow this guidance when you can because some car engines run more efficiently on regular gas, but others run optimally with premium higher octane gas. Engines in performance often have a high compression ratio, the difference in the size of the combustion chamber between the cylinder's lowest and highest points, so fuel with a higher octane level is required to continue to burn smoothly. 

Using regular gas won’t necessarily hurt your premium-guzzling engine, but you’re likely to lose some of its enhanced performance as the engine isn’t running optimally. Likewise, you can put premium gas in a regular car, but you won't feel any real benefit and it will cost you more money. 

In other words, if you accidentally put the wrong octane of gas in your car then it's nothing to worry about it, but it's best to not make a regular habit of it.

Can you mix premium and regular gas?

Sure, if you really want to. Once again, it is not advised to give a car any fuel with the wrong octane level, but there’s no indication that blending premium gas and regular gas would harm your engine. You’d essentially just be cooking up a mid-range octane level gas that’s unlikely to bring any real benefits to your engine.