Não informado. Drilling mud. National Lead, Baroid Sales Division.
Chicago-viite (17. p.)Não informado. Drilling Mud. Houston, Tex: National Lead, Baroid Sales Division.
MLA-viite (8. p.)Não informado. Drilling Mud. National Lead, Baroid Sales Division.
Varoitus: Nämä viitteet eivät aina ole täysin luotettavia.