Não informado. (1968). Annual Bulletin of Coal Statistics for Europe. United Nations, Economic Commission for Europe.
Chicago-referens (17:e uppl.)Não informado. Annual Bulletin of Coal Statistics for Europe. New York: United Nations, Economic Commission for Europe, 1968.
MLA-referens (8:e uppl.)Não informado. Annual Bulletin of Coal Statistics for Europe. United Nations, Economic Commission for Europe, 1968.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.