It's interesting to note that if you drive the average 15,000 miles per year ... increasing your MPG from say 32 to 35 mpg will only net you about $13 in savings per month. This is about 3 gallons of gas per month, which equates to about $156 per year in savings. This will obviously go down if you drive less, which is why this excel sheet works well to track your costs.
Increasing your mileage by changing from a huge SUV from 10mpg to a mid size car that gets 20mpg, will save you a lot more than going from a gas car that gets say 25mpg to a hybrid that gets even 50mpg. The cost savings aren't usually there unless you do huge miles.
I figured that I would have to drive over 40,000 miles a year to make it even compared to a Vibe (using average combined EPA mileage estimates ... and that's if I bought new). I would have to drive over 60,000 miles per year to justify a new Prius over my used 2007 Vibe that cost $11,800.
I'm also using this to determine if mods I make will be economical or not and to determine the ROI (return on investment) while figuring the impact of using less gas for the environment of course.
