Oligopoly is a fairly common market organization. In the United States, both the steel and automobile industries (with three or so large firms) provide good examples of oligopolistic market structures. Probably the most important characteristic of an oligopolistic market structure is the interdependence of firms in the industry. The interdependence, actual or perceived, arises from the small number of firms in the industry. Unlike under monopolistic competition, however, if an oligopolistic firm changes its price or output, it has perceptible effects on the sales and profits of its competitors in the industry. Thus, an oligopolist always considers the reactions of its rivals in formulating its pricing or output decisions. There are huge, though not insurmountable, barriers to entry to an oligopolistic market. These barriers can exist because of large financial requirements, availability of raw materials, access to the relevant technology, or simply existence of patent rights with the firms currently in the industry. Several industries in the United States provide good examples of oligopolistic market structures with obvious barriers to entry, such as the automobile industry, where significant financial barriers to entry exist. An oligopolistic industry is also typically characterized by economies of scale. Economies of scale in production implies that as the level of production rises, the cost per unit of product falls from the use of any plant (generally, up to a point). Thus, economies of scale lead to an obvious advantage for a large producer. There is no single theoretical framework that provides answers to output and pricing decisions under an oligopolistic market structure. Analyses exist only for special sets of circumstances. One of these circumstances refers to an oligopoly in which there are asymmetric reactions of its rivals when a particular oligopolist formulates policies. If an oligopolistic firm cuts its price, it is met with price reductions by competing firms; if it raises the price of its product, however, rivals do not match the price increase. For this reason, prices may remain stable in an oligopolistic industry for a prolonged period.