<P> The discussion of market structure in free economies as described by Adam Smith is often qualified or discussed in terms of patterns of market organization which serve the buyers and sellers in any particular form of the marketplace . Some types of market structure may be described using several recurrent types of descriptive organizational mechanism which may or may not dominate any particular market over time or at particular points in time, such as; </P> <P> 1 . Monopolistic competition, a type of imperfect competition such that many producers sell products or services that are differentiated from one another (e.g. by branding or quality) and hence are not perfect substitutes . In monopolistic competition, a firm takes the prices charged by its rivals as given and ignores the impact of its own prices on the prices of other . This market structure exists when there are multiple sellers who are attempting to seem different than each other . </P> <P> 2 . Oligopoly, in which a market is run by a small number of firms that together control the majority of the market share . </P> <Ul> <Li> Duopoly, a special case of an oligopoly with two firms . </Li> <Li> Monopsony, when there is only a single buyer in a market . </Li> <Li> Oligopsony, a market where many sellers can be present but meet only a few buyers . </Li> </Ul>

Economists define as a market structure with a few large firms