what determines the level of market power a monopolist can exercise
Market power A firm usually has market power by virtue of controlling a large portion of the market. In extreme cases—monopoly and monopsony—the firm controls the entire market. However, market size alone is not the only indicator of market power. Highly concentrated markets may be contestable if there are no barriers to entry or exit, limiting the incumbent firm's ability to raise its price above competitive levels.
Market (economics) In mainstream economics, the concept of a market is any structure that allows buyers and sellers to exchange any type of goods, services and information. The exchange of goods or services, with or without money, is a transaction.[1] Market participants consist of all the buyers and sellers of a good who influence its price, which is a major topic of study of economics and has given rise to several theories and models concerning the basic market forces of supply and demand. A major topic of debate is how much a given market can be considered to be a "free market", that is free from government intervention. Microeconomics traditionally focuses on the study of market structure and the efficiency of market equilibrium; when the latter (if it exists) is not efficient, then economists say that a market failure has occurred. However it is not always clear how the allocation of resources can be improved since there is always the possibility of government failure.