What two generalizations can be made about the pricing behavior of oligopolists?

Two interrelated characteristics of oligopolistic pricing have been observed. First, if the macroeconomy is generally stable, oligopolistic prices are typically inflexible (or "rigid" or "sticky"). Prices change less frequently under oligopoly than under pure competition, monopolistic competition, and, in some instances, pure monopoly. Second, when oligopolistic prices do change, firms are likely to change their prices together, suggesting that there is a tendency to act in concert, or collusively, in setting and changing prices.