Não informado. (2020). Petroleum Age. Petroleum Age Publishing Company.
Chicago-viite (17. p.)Não informado. Petroleum Age. Chicago, Ill: Petroleum Age Publishing Company, 2020.
MLA-viite (8. p.)Não informado. Petroleum Age. Petroleum Age Publishing Company, 2020.
Varoitus: Nämä viitteet eivät aina ole täysin luotettavia.