We observe different behavior patterns by producers across markets to a great degree. In some markets, producers are highly competitive; in others, they seem in some ways to coordinate their actions to avoid competing with one another; and, in some markets, there is no competition at all. For understanding markets and explaining the behaviors in them, economists have developed four principal models of market structure which are based on four dimensions:20 21 (1) the number of producers in the market, (2) the companies’ degree of pricing power, (3) whether the products offered are undifferentiated or differentiated (products that are different but viewed substitutable by customers), and (4) the market is consolidated or fragmented (market share for the leading four firms is equal to or less than 40% of total industry sales).