Axiomatic Cost and Surplus-Sharing

The equitable division of a joint cost (or a jointly produced output) among agents with different shares or types of output (or input) commodities, is a central theme of the theory of cooperative games with transferable utility. Ever since Shapley’s seminal contribution in 1953, this question has generated some of the deepest axiomatic results of modern microeconomic theory. More recently, the simpler problem of rationing a single commodity according to a profile of claims (reflecting individual needs, or demands, or liabilities) has been another fertile ground for axiomatic analysis. This rationing model is often called the bankruptcy problem in the literature. This Chapter reviews the normative literature on these two models, and emphasizes their deep structural link via the Additivity axiom for cost sharing: individual cost shares depend additively upon the cost function. Loosely speaking, an additive cost sharing method can be written as the integral of a rationing method, and this representation defines a linear isomorphism between additive cost sharing methods and rationing methods. The simple proportionality rule in rationing thus corresponds to average cost pricing and to the Aumann-Shapley pricing method (respectively in the case of homogeneous or heterogeneous output commodities). The uniform rationing rule, equalizing individual shares subject to the claim being an upperbound, corresponds to serial cost sharing. And random priority rationing corresponds to the Shapley-Shubik method, applying the Shapley formula to the Stand Alone costs. Several open problems are included. The axiomatic discussion of non-additive methods to share joint costs appears to be a promising direction for future research.