The purpose of this paper is to study the effects of entry into the market for a single commodity in which both sellers …’ payoffs may increase. The conditions under which entry by new sellers raises the equilibrium payoffs of existing sellers are … sellers, and encompass entirely standard economic environments. Similar results are derived relating to the entry of …

consumers we establish see-saws between consumers and advertisers. Entry of a lower-quality platform increases consumer surplus …, but decreases advertiser surplus if industry platform profits decrease with entry. Merger decreases consumer surplus, but …