Implementation of the socially optimal outcome

We show that a welfare maximizing planner in a Cournot oligopoly can easily implement the socially optimal outcome by offering the firms a per unit subsidy in return for upfront fees. The planner announces a subsidy and auctions it off to a limited number of firms. It is shown that if at least one firm is excluded and not subsidized, the socially optimal outcome can be achieved while the planner runs no deficit. The planner does not impose any regulation on the firms. They accept his offer willingly and voluntarily. Yet, every firm makes zero net profit and consumers extract the entire surplus.