King, F.W
English business letters : commercial correspondence for foreign students/F.W. King, D. Ann Cree.
Longmans , 1979
 Buku Teks SO
Bowman, Joel P.
Effective business correspondence
Harper & Row Publishers, 1979
 Buku Referensi
Aurner, Robert Ray
Manual for effective business correspondence
South-Western Publishing Company, 1939
 Buku Teks SO
Webster's guide to business correspondence
Merriam-Webster, Inc., 1988
 Buku Teks SO
De Vries, Mary Ann
The Elements of correspondence
Macmillan, 1994
 Buku Teks SO