Market purists consider oligopolies - not to mention cartels - to be as villainous as monopolies. Oligopolies, they intone, restrict competition unfairly, retard innovation, charge rent and price their products higher than they could have in a perfect competition free market with multiple participants. Worse still, oligopolies are going global. But how does one determine market concentration to start with? The Herfindahl-Hirschmann index squares the market shares of firms in the industry and adds up the total. But the number of firms in a market does not necessarily impart how low - or high - are barriers to entry. These are determined by the structure of the market, legal and bureaucratic hurdles, the existence, or lack thereof of functioning institutions, and by the possibility to turn an excess profit. The index suffers from other shortcomings. Often the market is difficult to define. Mergers do not always drive prices higher. University of Chicago economists studying Industrial Organization - the branch of economics that deals with competition - have long advocated a shift of emphasis from market share to - usually temporary - market power. Influential antitrust thinkers, such as Robert Bork, recommended to revise the law to focus solely on consumer welfare. These - and other insights - were incorporated in a theory of market contestability. Contrary to classical economic thinking, monopolies and oligopolies rarely raise prices for fear of attracting new competitors, went the new school. This is especially true in a "contestable" market - where entry is easy and cheap. An Oligopolistic firm also fears the price-cutting reaction of its rivals if it reduces prices, goes the Hall, Hitch, and Sweezy theory of the Kinked Demand Curve. If it were to raise prices, its rivals may not follow suit, thus undermining its market share. Stackleberg's amendments to Cournot's Competition model, on the other hand, demonstrate the advantages to a price setter of being a first mover. In "Economic assessment of oligopolies under the Community Merger Control Regulation, in European Competition law Review (Vol 4, Issue 3), Juan Briones Alonso writes: "At first sight, it seems that ... oligopolists will sooner or later find a way of avoiding competition among themselves, since they are aware that their overall profits are maximized with this strategy. However, the question is much more complex. First of all, collusion without explicit agreements is not easy to achieve. Each supplier might have different views on the level of prices which the demand would sustain, or might have different price preferences according to its cost conditions and market share. A company might think it has certain advantages which its competitors do not have, and would perhaps perceive a conflict between maximising its own profits and maximizing industry profits.