"If you have only one company -- and we call that a monopoly, of course -- you do have an issue. Most monopolies in the U.S. are going to be regulated by the government," Dr. Walden explains.

"Now another area, though, is where you have a few number of firms, maybe a handful. We call that an oligopoly, he adds. "Here you have to worry about those companies cooperating rather than competing -- that is, in being engaged in things like price-fixing.

"If that happens we call them collusive oligopolies, and they are actually illegal here in the U.S. They are not necessarily illegal everywhere in the world: OPEC is an example of a collusive oligopoly.

"There are two exceptions in the U.S. where collusive oligopolies are legal," he adds, "agricultural cooperatives and -- this will be very interesting to most people -- professional sports leagues."