In a perfectly competitive market an individual firm (seller) faces a perfectly elastic (horizontal) demand curve, set at the market price. With a horizontal demand curve, is there any consumer surplus? Why or why not? What does this indicate about the impact on consumers should a single firm shut down?
In any of the other market structures (oligopoly, monopolistic competition, or monopoly), the sellers face downward sloping demand curves. Is there any consumer surplus generated? Why or why not?