Não informado. (1957). Annual Bulletin of Gas Statistics for Europe. United Nations, Economic Commission for Europe.
Chicago-Zitierstil (17. Ausg.)Não informado. Annual Bulletin of Gas Statistics for Europe. Geneva, Suíça: United Nations, Economic Commission for Europe, 1957.
MLA-Zitierstil (8. Ausg.)Não informado. Annual Bulletin of Gas Statistics for Europe. United Nations, Economic Commission for Europe, 1957.
Achtung: Diese Zitate sind unter Umständen nicht zu 100% korrekt.