organization of the petroleum exporting countries. (2017). annual report 2017. grasl druck & neue medien gmbh.
Chicago-čujuhus (17. p.)organization of the petroleum exporting countries. Annual Report 2017. austria: grasl druck & neue medien gmbh, 2017.
MLA-čujuhus (9. p.)organization of the petroleum exporting countries. Annual Report 2017. grasl druck & neue medien gmbh, 2017.
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