Question

Why does an oligopoly only work if there are high barriers to entry in a market?

Answer 1

An oligopoly is the limitation of competition. If you can keep competitors out of the marketplace, you have more of a chance to make a profit. If you are in a business with a very high capital outlay or you have an extremely well trained labor force that your competitors can't match then you have effectively created or have created for you a very high barrier. Hence an oligopoly.