"I want a car with good fuel economy."

We hear that a lot, but what exactly constitutes good fuel economy? It would be easy to simply look at the EPA mpg ratings on a new car's window sticker, but what sort of mpg numbers can you expect in the real world? And what happens when you factor in the cost of fuel — gasoline, diesel and now electricity? This test seeks to answer those questions.Thankfully, there are not only a lot more fuel-efficient cars these days but also more fuel-efficient cars you wouldn't mind driving. When we did the first Fuel-Sipper Smackdown four years ago, there were no diesel-powered cars on sale, the wretched Smart Fortwo was the only gas-powered car with hypermiling capability and the Prius was the only serious hybrid. Back then, it seemed as if the only vehicles capable of 40 mpg were more like science experiments than real cars.

Then we tested a variety of new, more desirable cars in Fuel-Sipper Smackdown 2, and after dabbling last year in SUVs, we're back for another installment with a new set of appealing fuel sippers, and this time 40 mpg seems to be promised by every carmaker.