We present a Cournot model that compares the critical threshold of collusion in Duopoly and Oligopoly Markets where the actors are private, mixed or public. We assume that the incentive critical threshold for collusion depends on the interconnection fees. The different threshold values calculated in each Market structure are then estimated, using the OLS method, with variables related to the Tunisian market structures and prices. The Econometric estimation of the different threshold values is consistent with our theoretical results. Our findings can be used by the decision makers to control collusion, by acting on the level of interconnection fees for each market structure and by implementing the suitable market liberalization policies in this sector.