Não informado. (1968). Annual Bulletin of General Energy Statistics for Europe. United Nations, Economic Commission for Europe.
Παραπομπή σε μορφή Chicago (17η εκδ.)Não informado. Annual Bulletin of General Energy Statistics for Europe. New York: United Nations, Economic Commission for Europe, 1968.
Παραπομπή σε μορφή MLA (8th εκδ.)Não informado. Annual Bulletin of General Energy Statistics for Europe. United Nations, Economic Commission for Europe, 1968.
Πρόσοχή: Οι παραπομπές μπορεί να μην είναι 100% ακριβείς.