As coach travel gets more cramped, airlines have added “premium economy” sections that promise more space and comfort — often at a substantially higher price.

Air carriers have discovered many travelers are willing to pay two or even three times the prevailing economy fare to escape the crowded confines of coach. The extra money is mostly profit for the airlines, which is why so many now offer this class of service.

But what you get can vary dramatically by airline. In my latest for the Associated Press, how to avoid a wasting money on an upgrade that just isn’t worth it.