What information is needed for welfare-enhancing policies under international oligopoly

In the framework of international Cournot oligopoly, we analyze welfare-enhancing policies when policymakers have only limited information on demand and cost struc-tures. We show that even if policymakers have no idea about costs and demand, they can raise welfare by introducing a small production subsidy. If the government knows that demand is not very convex, a small tariff can be used to enhance welfare. With strategic complements, a small import reduction by an import quota deteriorates wel-fare while a small increase in the number of domestic firms improves welfare. In other cases, some more information is required to determine right policies