What, in a Oligopolistic Market, is Competitive Behaviour? -When is it most Likely to happen?

-This can be a Long Term Strat where the Firm does not Cooperate but Compete - especially on Price -Can be more Likely if One Firm has Lower Costs than all the other Firms -Or if there are quite a few Big Firms making it hard to Cooperate -Or if the Products made are Similar -Or if the Barrier to Entry is quite Low