A note on indeterminacy of unemployment equilibrium

According to Mortensen (1989), increasing returns to scale in matching may cause multiple equilibria if collective bargaining or efficiency wage is applied. I show that a unique equilibrium exists, also if the Nash bargaining solution is used, if productivity is constant. • A result about uniqueness of equilibrium in Mortensen (1989) is corrected. • Equilibrium is unique if productivity is independent of aggregate employment. • The corrected result holds also when the Nash bargaining solution is used.