  We study Cournot competition among firms in a networked marketplace that is
centrally managed by a market maker. In particular, we study a situation in
which a market maker facilitates trade between geographically separate markets
via a constrained transport network. Our focus is on understanding the
consequences of the design of the market maker and on providing tools for
optimal design. To that end we provide a characterization of the equilibrium
outcomes of the game between the firms and the market maker. Our results
highlight that the equilibrium structure is impacted dramatically by the market
maker's objective - depending on the objective there may be a unique
equilibrium, multiple equilibria, or no equilibria. Further, the game may be a
potential game (as in the case of classical Cournot competition) or not. Beyond
characterizing the equilibria of the game, we provide an approach for designing
the market maker in order to optimize a design objective (e.g., social welfare)
at the equilibrium of the game. Additionally, we use our results to explore the
value of transport (trade) and the efficiency of the market maker (as compared
to a single, aggregate market).
