Gaya APA
a.o, M, E, K. (1957).
The Coal Deposit From Ombilin. "Wedexro" 1957, Vol. 3, Fasc. 3. .
Bandung:
Pusat Sumber Daya Geologi.
Gaya MLA
a.o, Mining., Eng., Kless.
"The Coal Deposit From Ombilin. "Wedexro" 1957, Vol. 3, Fasc. 3.".
Bandung:
Pusat Sumber Daya Geologi,
1957.
Batubara.