Fixed Costs, Sunk Costs, Entry Barriers, and Sustainability of Monopoly
区分固定成本与沉没成本，指出足够大的固定成本能保证自然垄断者设定可持续价格，但固定成本本身不构成进入壁垒；沉没成本才是进入壁垒，并描述其福利后果。
This paper shows that (i) fixed costs of sufficient magnitude assure the existence of a vector of sustainable prices for the products of a natural monopolist—prices making him invulnerable against entry; (ii) nevertheless, fixed costs do not constitute barriers to entry; that is, they need not have undesirable welfare consequences; (iii) indeed, in market forms that we call perfectly contestable large fixed costs are completely compatible with many desirable attributes of competitive equilibrium; (iv) sunk costs do, however, constitute barriers to entry; and (v) finally, the profit and welfare consequences of entry barriers are described formally.