Index Universe tiene un post muy bien explicado sobre el costo de los ETFs (de energia) y como el mismo aumenta cuando hay Contango.
Let’s suppose that you (or the fund you own, such as USO) is holding the March oil contract (the “front month,” in futures terminology). As the expiration date approaches, you have to sell that contract. If you don’t, you’ll have to take delivery of physical oil in Cushing, Okla.—and let’s be honest, no one wants to do that.
So you sell the March contract and buy the April contract. This is called “rolling” the position, and it’s what most traditional commodity ETFs, including USO, do.
Now suppose that “spot” oil is trading for $75/barrel. As the March contract approaches expiration, its price will converge with the spot price. That’s the way the commodities market works. But if the markets are in contango, the April contract will cost more; say, $80/barrel.
You don’t lose any money when you sell the March contract and buy the April contract; you simply own fewer contracts at a higher price. The trouble happens over the next month. If the spot price of oil stays flat at $75/barrel, the value of that April contract will slowly decay from $80/barrel to $75/barrel.
That’s where you lose money; (…)