| TABLE 1 | SUMMARY OF MARKET STRUCTURES |
| | Perfect Competition | Monopolistic Competition | Oligopoly | Monopoly |
| Number of Firms | Many | Many | Few | One |
| Product | Homogeneous | Differentiated | Homogeneous or differentiated | Unique |
| Barriers to Entry or Exit? | None | Little to none | Substantial | Impenetrable |
| Strategic Interdependence? | No | No | Yes | Not applicable |
| Ability to Set Price (Market Power) | None | Limited | Some | Absolute |
| Long-Run Price Decision | P = ATC | P = ATC | P > ATC | P > ATC |
| Long-Run Profits | Zero | Zero | Usually economic | Economic |
| Key Summary Characteristic | Price taker | Product differentiation | Mutual interdependence | One-firm industry |