First of all, octane has NO effect on gas mileage. The reason why Acuras all recommend premium gas is that they have high compression engines. That compression ratio usually requires higher octane to not "knock". If you buy a tank of regular, and dont have knocking, then go ahead and use regular. I put regular in my RL. if you have knocking, then upgrade to Plus, and see if that stops the knocking. Sometimes you can fill halfway with regular, and top off with plus.