Equilibrium position of a firm under oligopoly

The firm under   oligopoly   earns abnormal   profits   both in the short and long run.     Equilibrium    is attained  at a point  where  marginal  cost  (MC)  curve  is equal  to the marginal  revenue   (MR) curve  and MC  curve  should  cut the MR  curve  from  below.

• From the graph, DKD is a kinked demand curve and K is the kink. Because of the kink, the MR curve is separated   by the discontinuous    gap, EF   into two MR curves.   The marginal   revenue curve above the gap is inelastic and the one below the gap is elastic.
• The discontinuity in the marginal   revenue   curve   implies   constant   revenue   as price and output remain fixed at the kink.
• Equilibrium is attained   at the  kink  where  MC is equal  to MR   in the  discontinuous  portion,   At equilibrium, output  OQ is produced   at the cost  price  OC  and  sold  at an administered price,  OP determined   at the kink.

The shaded area AKPC represents   the super normal profits.