Oligopoly is a market structure where there are only a few firms in the market due to barriers to entry. For example, the GSM market in Turkey is composed of a few firms such as Turkcell, Avea and Türk Telekom.. This industry is characterized with large economies of scale due to fixed costs and small and constant marginal costs. Hence large firms have an advantage over small firms and the industry is characterized with few large firms rather than many small firms.