What petrol, What car?
Modern cars with knock sensors; lower octane means less mileage. No damage.
Higher means no effect t or good mileage. Again, OK.
Older car, low octane, pings. Put in some hi test as soon as you can.
Hi octane in a car designed for regular., nothing, just waste of money.
If you put E85 in a car not designed for flex, will run like s***,. No damage, again put in proper octane 10% alky or less, ASAP.
Cars made at least as far back a 1980 run Fine on 10% Alky. Don't listen to Non-Owners of same that post to the contrary
I won't debate" Diesel" here, as you Indicated Petrol; Which is Gasoline..