Try ideas.uqam.ca/ideas/data/Articles/ ucpjpolecv:100:y:1992:i:6:p:1153-1207.html or do a Google search using OLIGOPOLISTIC .. there is plenty of info available
I seem to remember from my economics that an oligopoly is just like a monopoly, but with 2-10 competing firms accounting for the market, instead of the one in a monopoly.