capacity and strategic bundling. A firm usually has market power by having a high market share although this alone is not sufficient to establish the possession of significant market power. This is because highly concentrated markets may be contestable if there are no barriers to entry or exit. Invariably, this limits the incumbent firm's ability to raise its price above competitive levels. If no individual participant in the market has significant market power, anti-competitive conduct can only take place through collusion, or the exercise of a group of participants' collective market power. An example of which was seen in 2007, when British Airways was found to have colluded with Virgin Atlantic between 2004 and 2006, increasing their surcharges per ticket from £5 to £60. Regulators are able to assess the level of market power and dominance a firm has and measure competition through the use of several tools and indicators. Although market power is extremely difficult to measure, through the use of widely used analytical techniques such as concentration ratios, the Herfindahl-Hirschman index and the Lerner index, regulators are able to oversee and attempt to restore market competitiveness. Market structure In economics, market structure depicts how different industries are characterized and differentiated based upon the types of goods the firms sell (homogenous/heterogenous) and the nature of competition within the industry. The degree of market power firms assert in different markets are relative to the market structure that the firms operate in. There are four main forms of market structures that are observed: perfect competition, monopolistic competition, oligopoly, and monopoly. Perfect competition power The concept of perfect competition represents a theoretical market structure where the market reaches an equilibrium that is Pareto optimal. This occurs when the quantity supplied by sellers in the market equals the quantity demanded by buyers in the market at the current price. Firms competing in a perfectly competitive market faces a market price that is equal to their marginal cost, therefore, no economic profits are present. The following criteria need to be satisfied in a perfectly competitive market: Producers sell homogenous goods All firms are price takers Perfect information No barriers to enter and exit All firms have relatively small market share and cannot influence price As all firms in the market are price takers, they essentially hold zero market power and must accept the price given by the market. A perfectly competitive market is logically