Efficient trading on a network with incomplete information

This paper considers a trading problem on a network with incomplete information. We consider a simple water trading problem in which three agents are located in a linear order along a river. Upper stream agents can sell some amount of the water to their downstream but not the other way around. The middle agent can be both a seller and a buyer. Agents have private information on their utility of water, which we assume is non- linear. We ask if there is an efficient trading mechanism for the allocation of water. We show that if agents have highly asymmetric initial endowments of water, incentive-compatible, individually rational, budget-balanced mechanisms exist that are also ex-post efficient.