What causes monopolies? A legal fiat; e.g. US Postal Service A patent; e.g. a new drug Sole ownership of a resource; e.g. a toll highway Formation of a cartel; e.g. OPEC Large economies of scale; e.g. local utility companies5 What causes monopolies? A legal fiat; e.g. US Postal Service A patent; e.g. a new drug Sole ownership of a resource; e.g. a toll highway Formation of a cartel; e.g. OPEC Large economies of scale; e.g. local utility companies