Is equilibrium necessary in the oligopoly market structure?

According to economic theory, equilibrium happens in every
market structure (in the long run) so long as the government does not set a price floor
or a price ceiling.  Therefore, equilibrium is necessary in a market that is an
oligopoly as long as the price of the good or service is allowed to move
freely.

When economists speak of market equilibrium, they
are speaking about the situation in which the quantity supplied and the quantity
demanded are the same.  This situation occurs at a particular price level.  At that
price, the amount of the product that the suppliers provide and that consumers demand is
the same and the market is said to be in equilibrium.

As
long as the price is free to move, equilibrium will be reached because suppliers will
change their prices if needed.  If there is a market surplus, they will lower their
prices.  If there is a market shortage, they will raise their prices.  In these ways,
equilibrium will always be reached in an oligopoly where the price is free to
move.