Não informado. (1957). Annual Bulletin of Gas Statistics for Europe. United Nations, Economic Commission for Europe.
শিকাগো স্টাইল (17 তম সংস্করণ) উদ্ধৃতিNão informado. Annual Bulletin of Gas Statistics for Europe. Geneva, Suíça: United Nations, Economic Commission for Europe, 1957.
M.L.A (8 ম সংস্করণ) উদ্ধৃতিNão informado. Annual Bulletin of Gas Statistics for Europe. United Nations, Economic Commission for Europe, 1957.
সতর্কবাণী: সাইটেশন সবসময় 100% নির্ভুল হতে পারে না.