Steward I
For lower MPGs, small differences represent major savings, while at higher MPG the savings diminish quickly. For a 1000 mile drive, 5 MPG is 200 gallons, and 7 MPG is 143 gallons, so that 40% increase of 2 MPG saved you 57 gallons of fuel. 20 MPG is 50 gallons, and 28 MPG is 36 gallons, so that 40% increase of 8 MPG saved you 14 gallons of fuel. 30 MPG is 33 gallons, and 42 MPG is 24 gallons, so that 40% increase of 12 MPG only saved you 9 gallons of fuel.