I have a Scion FRS that I use to commute 125 miles every day (round trip). My average mpg is 30.5. But I started hypermileaging a couple months ago. I now get between 36 and 38 mpg depending on the weather (wind and rain ding it).
I have a 13 gallon tank. This works out to an additional 72 miles per tank, using the 36 mpg number or 100 miles using the 38 mpg. Using the 30.5 number, that’s like getting either 2+ extra gallons or 3.35 extra gallons. At $3.70 per gallon that means between $7.50 and $11 per tank savings. That is huge.
And that doesn’t take into account that I don’t make as many trips to the gas station.
It’s how I do my part to not feed the oil companies any more than I have to.
I telecommute and walk or ride my bike for any errand < 5 miles and doesn’t require the cargo capacity of a vehicle. A tank of gas lasts a month. :-)