Which of the following types of competition is most common in oligopolistic markets?

In oligopolistic markets, non-price competition is most common because firms often find that engaging in price competition can lead to price wars, which can be detrimental to all players involved. Since a few firms dominate the market, each firm's pricing strategy is highly interdependent on the actions of its rivals. As a result, instead of lowering prices to attract customers, firms in an oligopoly frequently focus on non-price strategies such as advertising, product differentiation, and improving customer service.

These non-price methods allow firms to maintain their market share and profitability without engaging in destructive price competition. For instance, companies might compete on the basis of quality, branding, or innovation, which can create a more stable business environment and enable firms to capture a larger consumer base without cutting prices.

The other types of competition mentioned don't typically characterize oligopolistic markets. Perfect competition involves many firms and price-taking behavior, while monopolistic competition, though resembling oligopoly in that firms differentiate their products, still lacks the same interdependence and concentration typically seen in oligopoly. Therefore, non-price competition is the defining feature of competition in oligopolistic markets.