Is it the fuel? Not really. Even though giant passenger jets do guzzle down fuel at a ridiculous 0.67 miles per gallon--seriously, they need 1.5 gallons of jet fuel for every mile traveled--there are so many people on an airplane that the fuel cost gets split down to a much more reasonable price: a per-person fuel efficiency of 104.7 miles per gallon. That's good! So why is flying so expensive? It's everything else.