In which market structure are sellers numerous but not powerful enough to influence prices or supply?

The market structure where sellers are numerous but not powerful enough to influence prices or supply is pure competition. In this structure, there are many buyers and sellers in the market, and each firm sells a homogeneous product. Because of the large number of competitors and the similarity of goods, no single seller has significant control over the market price. Prices are determined by overall market supply and demand, leading to what is termed "price takers" behavior among firms. Each seller must accept the prevailing market price and cannot influence it through their own supply levels.

In pure competition, the ease of entry and exit into the market ensures that firms can only earn normal profits in the long term. This characteristic promotes efficiency, as firms must operate at their lowest possible cost to remain competitive. While other market structures, such as monopoly and oligopoly, feature a limited number of sellers that can significantly influence market conditions, pure competition is defined by many sellers without the power to sway pricing or supply decisions.