Let's keep the concepts clear on "textbook oligpoly." Economic theories of oligopoly show that ANY outcome, from perfectly competitive to monopoly to in-between, can happen in oligopoly. The outcome depends on a lot of specific facts and circumstances. (Sorry, no link, but consult that old microeconomics textbook on your shelf, in the chapters that discusses market structures.) So the mere fact that something is an "oligopoly" (relatively small number of sellers) says absolutely nothing about what type of conduct or results inevitably follow.