It's a simple! Pump your tyres to the proper pressure. Your car will roll better, and if we all did it we'd save 7% of our daily fuel bill.
So next time you fill up, scoot over to the tyre pump. It costs nothing, plus you will get better tyre life too - all straight into your hip pocket.
Now, compare this to one option, floated by "Big Oil" - Lets get another 5% of oil the hard way - by drilling in sub zero temperatures and in the process destroying Antarctica.
Think about this for just 2 seconds - less benefit at a higher cost - not smart energy.
Now, for even better mileage, ride your bike.