https://www.google.de/search?q=A+New+Look+at+Oligopoly%3A+Implicit+Collusion+Through+Portfolio+Diversification&ie=utf-8&oe=utf-8&client=firefox-b&gfe_rd=cr&ei=zZ00V6H9Ns-GOpmpg5AJ
Go to speaker website. View seminar paper.