Can you mix 87 octane and 91 octane?

Yes. Mixing 87 octane and 91 octane gasoline is perfectly safe and acceptable. When you mix two different octane ratings, the resulting octane rating will be somewhere between the two. Mixing a gallon of 87 octane and a gallon of 91 octane will result in two gallons of approximately 89 octane fuel.

There is no harm in mixing different octane ratings as long as you are using unleaded gasoline. In fact, some people believe that mixing different octane ratings can actually improve performance and fuel economy. However, there is no scientific evidence to support this claim.

If you are not sure what octane rating your car requires, you can always check your owner's manual. Most cars require regular 87 octane gasoline, but some high-performance cars may require premium 91 octane gasoline. If you are not sure, it is always best to err on the side of caution and use the higher octane gasoline.