In addition to only being a few firms, there are other defining characteristics in an oligopoly.

1. Strong barriers to entry. Unlike a monopoly, however, these barriers prevent most, but not all potential entrants from coming into the market.
2. Long run profits are possible. These are not guaranteed, but unlike perfect competition and monopolistic competition, a firm can make profits in the long run in an oligopoly.
3. Homogeneous or heterogeneous product. The firm's products can be either identical or slightly differentiated compared with its competitors.