In economics and general equilibrium theory, a perfect market is defined by several conditions, collectively called perfect competition. Perfect information – All consumers and producers know all prices of products, homogeneous products – The products are perfect substitutes for each other. Well defined Property rights – These determine what may be sold, profit maximization of sellers – Firms sell where the most profit is generated, where marginal costs meet marginal revenue. Rational buyers, Buyers make all trades that increase their economic utility, No externalities – Costs or benefits of an activity do not affect third parties. This criteria also excludes any government intervention, zero transaction costs – Buyers and sellers do not incur costs in making an exchange of goods in a perfectly competitive market. Non-increasing returns to scale and no network effects – The lack of economies of scale or network effects ensures that there always be a sufficient number of firms in the industry. This equilibrium will be a Pareto optimum, meaning that nobody can be better off by exchange without making someone else worse off. Such markets are efficient, as output will always occur where marginal cost is equal to marginal revenue. But perfectly competitive markets are not necessarily productively efficient as output will not always occur where marginal cost is equal to average cost, in perfect competition, any profit-maximizing producer faces a market price equal to its marginal cost. This implies that a factors price equals the marginal revenue product. It allows for derivation of the curve on which the neoclassical approach is based. This is also the reason why a monopoly does not have a supply curve, the abandonment of price taking creates considerable difficulties for the demonstration of a general equilibrium except under other, very specific conditions such as that of monopolistic competition. Real markets are never perfect, but range from close-to-perfect to very imperfect, share and foreign exchange markets are commonly said to be the most similar to the perfect market. The real estate market is an example of an imperfect market. In a perfect market the sellers operate at zero economic surplus, normal profit is a component of costs and not a component of business profit at all. It represents the opportunity cost, as the time that the owner spends running the firm could be spent on running a different firm. In other words, the cost of normal profit varies both within and across industries, it is commensurate with the associated with each type of investment. Only normal profits arise in circumstances of perfect competition when long run equilibrium is reached
Only in the short run can a firm in a perfectly competitive market make an economic profit.
A monopolist can set a price in excess of costs, making an economic profit (shaded). The above Picture shows a Monopolist (only 1 Firm in the Industry/Market) that obtains a (Monopoly) Economic Profit. An Oligopoly usually has "Economic Profit" also, but usually faces an Industry/Market with more than just 1 Firm (they must share available Demand at the Market Price).
In the short run, it is possible for an individual firm to make an economic profit. This situation is shown in this diagram, as the price or average revenue, denoted by P, is above the average cost denoted by C .
However, in the long run, economic profit cannot be sustained. The arrival of new firms or expansion of existing firms (if returns to scale are constant) in the market causes the (horizontal) demand curve of each individual firm to shift downward, bringing down at the same time the price, the average revenue and marginal revenue curve. The final outcome is that, in the long run, the firm will make only normal profit (zero economic profit). Its horizontal demand curve will touch its average total cost curve at its lowest point. (See cost curve.)