Environmental Taxes in Duopoly with Soft Capacity Constraints

This paper examines an environmental tax when duopolistic firms engage in capacity-price competition. Under soft capacity constraints, the equilibrium ranges from Bertrand competition to Cournot competition, depending upon parameters. It is shown that a unit tax potentially changes the qualitative nature of equilibrium. That is, the type of tax affects the mode of competition between firms. This effect gives rise to the result that a unit tax is sometimes an inefficient instrument. The explanation is that the tax that leads to the first-best under Cournot competition will in fact sustain Bertrand competition, and vice versa.