A note on the excess entry theorem in spatial markets

Vickrey [Vickrey, W.S., 1964. Microstatics, Harcourt, Brace and World, New York] shows that the number of firms entering is excessive in his circle model of product differentiation. We broaden his result to a large class of transport and production cost functions; in particular, convex transport and production costs always entail excessive entry as long as a price equilibrium exists. We also provide an example of insufficient entry in equilibrium.