Market can be defined in the shortest and the narrowest way as a relation of supply and demand. During the exchange of goods and services, the "benefit" of the same can be measured and is defined as economic welfare. Economic welfare shows how much is the buyer prepared to pay for a product without backing out of the trade as well of how much the seller is willing to lower the price to make the sale. In condition of perfect competition, there are many sellers and buyers and all the information needed is freely available. In that case the market sets the price itself since there are multitudes of sellers for the same product. In these conditions does the best ratio of consumer and seller welfare come to life. On the other end of the spectrum is monopoly which is characterized by having only one seller of a product versus multitude of buyers. In this condition, the amount of the product is restricted and it has no substitute therefore the monopoly owners create their own price policy. This way the consumer is forced to give up on his surplus in order not to lose the product. Between these two extremes, one can find monopolistic competition market and oligopoly market. In monopolistic competition market, the seller produces slightly different products and the enterprises can freely enter and leave the commodity market. In these conditions, the ration of consumer and seller surplus will depend on the price margin above marginal cost or upon outside interference. The movement of this system to either extreme mentioned before depends on which characteristic is the dominant in the system (price margin for absolute competition and outside interference for monopoly). On the other hand, there is oligopoly system which is much closer to monopoly market than it is to perfect competition. Oligopoly market is characterized with few sellers compared to multitude buyers while retaining the ability to set prices. In these conditions, each enterprise attempts to take as bigger market segment as it can in order to supply the same, thereby maximizing their profit while simultaneously blocking their rivals from the same segment. Basic example of oligopoly is duopoly which is comprised of two rivals. Each of the rivals attempts to take the biggest market segment as they can. Once the balance is formed (most likely by each of the competitors having one third of the market) the price will level out on the price that is less than price in monopoly, but greater than in perfect competition.