organization of the petroleum exporting countries. (2017). annual report 2017. grasl druck & neue medien gmbh.
Citazione stile Chigago Style (17a edizione)organization of the petroleum exporting countries. Annual Report 2017. austria: grasl druck & neue medien gmbh, 2017.
Citatione MLA (9a ed.)organization of the petroleum exporting countries. Annual Report 2017. grasl druck & neue medien gmbh, 2017.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.