En quête d'un indice de l'intensité de la concurrence réflexions sur l'indétermination de l'équilibre oligopolistique

The intensity of competition is viewed here in the specific form of the competitive toughness exhibited by a firm towards its competitors, as reflected in its market stra- tegies (prices and quantities). The competitive environment, resulting in particular from former choices, concerning entry, location in the characteristics space or tech- nology, is taken as given. A concept of equilibrium in a homogeneous or differentia- ted oligopoly is used, where simultaneous price and quantity choices must satisfy two constraints : an individual constraint on the market share and a collective cons- traint on market size. The relative weight of the multiplier which is associated with the former constraint may be taken as an index of the competitive toughness of any active competitor at a given equilibrium. We thus obtain a parametrisation of the equilibria, leading to a unified approach of the static theory of oligopolistic competi- tion. The very number of active competitors within a population of potential produ- cers is a supplementary index of competitive toughness characterizing an equili- brium. Some considerations on the macroeconomic use of such indices of competitive toughness conclude the paper.