I have only had mine a few weeks and I'm very interested because our delta here on Reg vs. Prem is $.50/gal. I have run 1 tank of each with no noticeable diff but going to go back and and test more because they were not apples-to-apples. I'm average 21.2 MPG with mix of city/highway but more city than highway. Either way it's a better option than my previous 2005 car that was doing 15 MPG (so still saving at least $450/yr on gas at a minimum.)