Many key industries (e.g., biomedical, pharmaceuticals, telecommunications, and information technologies) are characterized by cumulative innovations, where the introduction of a new product or service often requires many complementary technologies. When these technologies are protected by intellectual property rights owned by many firms, patent thickets exist, which researchers have argued may hinder the development of cumulative innovations. Specifically, patent thickets may lead to excessive royalty burdens for potential licensees, which is called "royalty stacking," and if such costs are passed on to consumers, prices of products based on cumulative technologies will be driven up, dubbed as "double marginalization." The literature, however, does not address these issues under different forms of licensing contracts. This article develops a game-theoretic model where a downstream firm seeks to license N patents that read on its product from upstream firms. It discusses a variety of licensing forms widely used in practice and attempts to discover whether royalty stacking and double marginalization occur under these forms of licenses. It also studies the impact of bargaining power between parties. It is found that when patent ownership becomes more fragmented, neither royalty stacking nor double marginalization occurs under profit-based royalty, fixed fee, and hybrid licenses. Such problems occur only under pure quantity-based or pure revenue-based royalty licenses when the downstream firm's bargaining power is low. It is also shown that no matter how fragmented the ownership structure of patent is, hybrid licenses consisting of a fixed fee and a quantity-or revenue-based royalty rate lead to the same market outcomes as a fully integrated firm that owns all the patents and the downstream market. This article has interesting implications for both research and practice. First, the results show that even under the same patent ownership structure, different forms of licenses lead to quite different market outcomes. Therefore, it is suggested that firms and policy makers pay more attention to contractual forms of licenses when trying to minimize the negative impact of patent thickets. Second, the extant literature has largely assumed that quantity-based royalties are used, where double marginalization is the most severe. In practice, revenue-based royalties are most common, under which double marginalization is much milder. Third, the results show that patent pools can be most effective in mitigating royalty stacking and double marginalization when quantity-based or revenue-based royalties are the sole or primary payment form, especially when downstream firms have low bargaining power.
