Well, I've gone through two tanks of gas and show an increase of 1 MPG. i know that don't seem that good but this is all short trip stop an go driving. it's only a 2 minute drive to work so it took a wile to get through 2 tanks. and i say every bit helps, when i first got my VX i was getting 11 MPG and now( after much work) I'm get 16 MPG. it looks like my first highway test will be my trip to MOAB next year.