A really useful link relating to Oligopoly for Economics Students, see the relevant section in the specification below:-
http://www.bbc.co.uk/news/business-41384179
Edexcel spec reference  3.4.4 Oligopoly         
AQA spec reference 4.1.5.5 Oligopoly
OCR spec reference Page 12 Oligopoly
All Economics can be found on our website https://www.apt-initiatives.com/