Mrs John Robinson- 'Oligopoly is market situation in between monopoly and perfect competition in which the number of sellers is more than one but is not so large that the market price is not influenced by any one of them'.
Prof. George J. Stigler- 'Oligopoly is a market situation in that a firm determines its marketing policies on the foundation of expected behaviour of close competitors'.
Prof. Stoneur and Hague- 'Oligopoly is different from monopoly on one hand in that there is a single seller, conversely, it differs from perfect competition and monopolistic competition also in that there is a large number of sellers. Or we can say that whiledescribing the concept of oligopoly, we comprise the concept of a small group of firms'.
Prof. Left Witch- 'Oligopoly is a market situation in that there are a small number of sellers and activities of each seller are significant for others'.
So oligopoly is a market situation in that a few firms producing an identical product or the products, that are close substitutes to each other as well as compete with each other.