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.