International Petroleum encyclopedia 1990
editor, John C. McCaslin
PennWell Publishing , 1990
 Buku Referensi
Stokes, Adrian V.
Concise encyclopedia of information technology / Adrian V. Stokes
Wildwood House, 1986
 Buku Referensi
Pandey, A.K., author
Encyclopedia of fishes and fisheries of India : volume-V
Anmol Publications, 1992
 Buku Referensi
The World book encyclopedia : volume 18, U-V
Field Enterprises Educational Corporation, 1963
 Buku Referensi
Rhodes, V. James
The agricultural marketing system / V. James Rhodes
Grid Publishing, Inc, 1978
 Buku Teks
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