I hate posts like this. I will not go into a rant, but let’s say you save $0.10 per gallon so that’s what, X 15 $1.50 per tank, or double it to .20 and that’s $3.00 per tank!! Also I laugh when people do it for another reason, the car will retard spark and performance, with a high compression ratio engine like ours, your MPG will suffer when the engine cuts back, so to go 60mph will take more energy with lower octane gas, than with higher octane gas, so you might actually pay MORE by having to fill up more often by using cheaper lower octane fuel.