(FORTUNE Magazine) – When you buy a ticket for just about anything--from a Motley Crue concert to a seat on a Greyhound bus--you're free to use it yourself or give it away to anyone you choose. That's the way tickets work, right? Why is it, then, that when you can't make the meeting in Dallas and want to give that ticket to a colleague, the airline won't let you? Why, in other words, are airline tickets nontransferable?

If you think the answer is security, you're wrong. According to the FAA, carriers must request passenger identification, but there is no requirement that tickets be nontransferable. And the Air Transport Association says it's a choice made by individual airlines. So why don't most airlines allow it?

According to United spokesperson Tony Molinaro, the policy is designed to prevent fraud and reduce the airline overhead that ticket swapping would entail. It also protects the airlines' bottom lines: Because of the peculiar nature of airline tickets' pricing structure, whereby fares typically skyrocket as the travel date nears, Molinaro notes that they could fall prey to speculators, who would snap up blocks of tickets at the reduced prices and then resell them later, undercutting the airlines' last-minute fares. Nontransferability prevents such shenanigans, which have the potential to completely undo the airlines' fragile economics.

Doesn't this simply mean, in the end, that tickets are nontransferable so the airlines can make money? "Yeah," says Molinaro, "that's probably true."

--Erin Davies

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