For a monopoly to persist, the market must be closed to entry

For a monopoly to persist it is important that there are entry barriers for the new firms. The barriers to entry can be created in the following ways:

1. Exclusive ownership of the resources: The companies enjoying exclusive ownership of the intermediate goods and factor inputs will restrict any other firms entering into the domain. The supply of crude oil in the world can only be done by the countries have exclusive rights of the oil wells. These nations have their cartel and enjoy monopoly power in the world.

2. Government regulations and restrictions: The government may impose a restriction on the entry of new firms in certain sectors of strategic importance like defense supply.

3. Patents and Copyrights: The companies may apply for exclusive rights to produce and supply of certain goods. Google Pagerank is an example of patent rights owned by the company.