When and how do entrepreneurs sell their inventions? To address this issue, we develop an endogenous entry-sale asymmetric information oligopoly model. We show that lowquality inventions are sold directly or used for own entry. Inventors who sell post-entry use entry to credibly reveal information on quality. Incumbents are then willing to pay high prices for high-quality inventions to preempt rivals from obtaining them. Using Swedish data on patents granted to small firms and individuals, we find evidence that high-quality inventions are sold under preemptive bidding competition, post entry.