Top 10 cities in the usa for This can be the case if only a single firm possesses the particular expertise on how to produce something at low enough costs to supply the market. A third factor that may prevent firms from entering a market is that they do not have access to critical resources. Thus, as an example, the aluminum company Alcoa managed to purchase the mining rights to most readily available bauxite. As bauxite is a principal mineral in the production of aluminum, potential competitors in the aluminum market were denied access to a key scarce resource. A fourth reason that additional firms may not enter a market has to do with the particular technology used to produce the good or service in conjunction with the market size that is being supplied. For instance, a small municipality may not have enough residents to cover the large overhead costs associated with the provision of a sewer system for more than one company. Such instances are referred to as natural monopolies (see below), because it may be the case that no second firm would ever want to enter the market to begin with (since if they did enter, they would make a loss). Top 10 cities in the usa 2016.