When I see a large pickup truck or tractor trailer driving 65 mph, I often wonder, “how often do they fill up”? A standard tractor’s diesel engine hauling a trailer will manage 5 to 7 mpg, where the gasoline burning tractor can get about 3 mpg. I just recently purchased a Kia Forte Eco which is rated to 37 mpg highway. I can travel 100 miles for under 10 dollars. It would cost a tractor trailer over 60 dollars to make the same trip on diesel ($112 using gas).