Inferior factor in Cournot oligopoly

The condition for factor inferiority has been well known for a competitive firm facing perfect competition in both product and factor markets. Whether the factor inferiority is observable or not has been unknown for oligopoly facing perfect competition in factor market. We derive a general condition for the factor inferiority in Cournot oligopoly without product differentiation. We derive it on the basis of a novel technique for proving the existence of a unique Cournot equilibrium industry output.