The government has granted the U$.$S$.$ Postal Service the exclusive right to deliver mail.

There are several dozen crust makers that distribute their frozen products to hundreds of pizza shops nationwide. The shop owners source crusts from the cheapest available producer.

A few major airline companies represent a great majority of total air travel. Consumers consider all different flights to be essentially the same, and comparison shop for the lowest price.

In a large city, one chain of coffee shops controls a large market share because locals believe its coffee tastes better than that of its competitors.