Which market structure is characterized by firms that have no market power and create no barriers to market entry?

A monopoly exists when a single firm dominates the market, possessing significant market power and the ability to set prices above equilibrium levels. This structure inherently creates high barriers to entry, preventing other firms from entering the market and competing, which is the opposite of the characteristics described in the question.

Monopolistic competition features many firms that sell similar but differentiated products, allowing some degree of market power to influence pricing. While there are relatively low barriers to entry, firms still exert market power due to product differentiation, meaning they do not strictly fit the criteria of having no market power.

An oligopoly is characterized by a few firms that dominate the market, leading to significant market power among those firms. This market structure often results in barriers to entry due to the strategic interactions and potential collusion between firms, which directly contradicts the conditions of no market power and no barriers.