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The value of patent rents is an important quantity for policy analysis. However, estimates in the literature based on patent renewals might be understated. Market value regressions could provide validation, but they have not had clear theoretical foundations for estimating patent rents. I develop a simple model to make upper-bound estimates of patent rents using regressions on Tobin's Q. I test this on a sample of US firms and find it robust to a variety of considerations. Estimates from market value regressions correspond well with estimates based on patentee behavior generally, but renewal estimates might be understated for pharmaceuticals.

Patents are intended to provide an economic incentive for invention by granting the patent holder an exclusive right for a limited period. This right to exclude allows a patent-holding firm to become a monopolist or, perhaps more often, to achieve some lesser degree of market power, either in product markets or in the market for technology licenses. This market power, in turn, is supposed to permit the firm to earn supra-normal profits, “rents,” that are an economic incentive to invent.

The model developed in this paper shows that clear but limited inferences can be drawn about the magnitude of patent rents from market value regressions. Coefficient estimates from carefully specified equations can be interpreted as upper-bound estimates of the discounted value of future rents earned by patents. Moreover, I show that that these estimates are robust to a variety of considerations including the possibility that a “fat” upper tail in the distribution of patent values may make finite sample estimates unreliable.