We have the saying in economics that "All industry gravitates towards Oligopoly

At a time all industries move towards oligopoly. When a firm enters a market at the initial stage it remains as a small firm with time it gradually grows and move towards being a large firm in the economy and gravitates towards oligopoly. It is because at a time the firms depend on each other for their different decisions such as total output production and its price, advertising cost and others which is the characteristics of oligopoly market structure.

Yes, Oligopoly have the potential to act like monopoly. From the definition of oligopoly, we have seen that it consists of small number of large firms, these firms can come together to form a cartel and can control price and quantity in the economy like a monopoly for their individual profit. Such an example is OPEC.