If you mix 87- and 91-octane gas in your vehicle, your engine won't fall out into the street. But will it damage your vehicle? Here's what happens.

"My advice would be to run one octane or the other," says Stephen Leroux, professor in the school of transportation at Centennial College in Toronto. "I see no benefit in mixing." ...

If you’re mixing and want to err on one side, go heavier on the higher octane just to be sure. When the cost hit $75.00, the pump shut off automatically with 14.4 gallons dispensed.

If higher-octane fuel isn’t available, a one-time mix of 91 and 95 RON might not cause immediate harm, but it’s essential to refill with the correct grade at the earliest opportunity.

The truth is that mixing regular and premium gas shouldn't be a problem. In most engines, it won't hurt anything except your gas budget. But you shouldn't be doing it, either.

Mixing unleaded and super unleaded petrol is safe for you and your car. Unleaded has an octane rating of 95 while super unleaded is 98 and designed to be more fuel efficient with a smoother engine ...