At 20 MPG and 12,000 miles per year (limit) that would be 600 gallons per year times 3 for a total of $1,800.00 at 3.99 per gallon. If you got 30 miles per gallon it would be $400.00 per year or $1,200.00. If it went to $4.99 per gallon you would double that amount etc. They are betting it will level off and go down a bit. It is still a lot cheaper than cash incentives. Also over the 3 year period they will be making interest on the money they would have givin you up front as an incentive. Brilliant marketing unless things really go crazy.