Now here's a fee that airline fliers might actually like. On some flights, you can pay to ensure the seat next to you is empty.

No U.S. airline is offering this option, but three international airlines seem to be finding success with the idea. Air New Zealand, AirAsia X in Malaysia and Spain's Vueling all sell the empty seat next door for fees ranging from $6 to $60, The New York Times reports.

But there's one caveat: If the flight is full and the airline needs that seat for someone else, you'll get your money back.

AirAsia X is advertising the offer with a photo of a woman sleeping across three airline seats. That airline lets people buy out the whole row if they want to stretch out.

This fee works on so many levels. Airlines hate having empty seats. One consulting firm recently found that network carriers like Alaska Air (ALK) and Delta Air (DAL) had to fill 87% of the seats on their domestic flights just to break even, The Wall Street Journal reports.

The so-called "empty seat option" allows airlines to recoup some of that lost revenue while keeping passengers happy. And, as Jetblue Airways (JBLU) Southwest Airlines (LUV) can tell you, doing things to earn customer goodwill pays off in the long run.

For passengers, the benefit is obvious.

So why aren't more airlines doing this? Some are focused on a different approach to seating: letting passengers choose their seatmates on Facebook or LinkedIn (LNKD). When people make reservations with KLM or Malaysia Airlines, for example, they also can choose to make their Facebook profile visible to other passengers. If enough people do this, you might get a general idea of whom you're sitting next to.

And there may be some times when fliers are happy to make conversation with their neighbors. Other times, they might be loaded down with work or just plain tired -- making an empty seat the best traveling companion of all.