Long Run Equilibrium of Oligopolies The long run equilibrium of a perfectly competitive market is well established. My question is - are the concepts of a long run equilibrium in a perfect competition extendable (analogous or otherwise) to an oligopoly, specifically considering the the Cournot model and the Bertrand model. 

Suppose I want to find the equilibrium number of firms $ N $ in a Cournot model, for example - will the approach be similar to that of a perfect competition?
The 'long run' assumption is not about whether the firms already on the market are price takers (perfect competition) or oligopolists but whether entry to the market is free. If entry to the market is free then in the long run profits tends toward zero, as a profitable market makes it tempting for more firms to enter.

If you have special asymmetric conditions where some entrants have different cost functions than the new ones the zero profit condition may not hold even in the perfect competition case.