What is OPEC, and how does it relate to the different market structures such as perfect competition, monopolistic competition, oligopoly, and monopoly?

Do you think OPEC has been equally successful in maintaining high oil prices both in the short run and in the long run? Do you think OPEC's success or failure can be explained using the concepts of price elasticity of demand and supply and how it varies between the short run and the long run?

How does the theory of oligopoly and cartel behavior fit in your analysis of OPEC's role in influencing global oil prices? In recent years have they faced any competition from non-OPEC members?

Don't forget to put the link/sources used to answer these questions.