Perfect Competition	Monopolistic Competition	Oligopoly	Monopoly
Number & Size  of Firms	unlimited number; very small; none has market power	many; various sizes; each seeks mkt. power over a market segment	very few; extremely large; each able to influence industry Q & P	one; various sizes; total market power; sole dominance over industry
Pricing Behavior	price-takers. firm takes Prices, costs decides Q to maximize profit. P =MR = MC = ATC	each firm tries to gain monopoly pricing power over a market segment via location, advertising, brand name recognition, consumer loyalty. P maybe greater than or equal to ATC.	oligopolistic firms have unlimited strategies; can collude, go-it-alone, or damage each other. P maybe greater than, equal to, or less than ATC.	price-maker; monopolist reduces Q to raise P > ATC.
Economic Profit	zero economic profit.	zero or positive economic profit	positive, zero, or negative economic profit.	positive economic profit.
Barriers	None	Low	High	Highest
Product	Identical	Differentiated	Substitutes	Unique