Resources found in the Smithsonian National Postal Museum Library are:
- Ward, Jr. P.H. “PANAMA – The Issue of 1906 – Part 1.” Collectors Club Philatelist. Vol. XXVII , No. 2, p.23 – 29.
- Ward, Jr. P.H. “PANAMA – The Issue of 1906 – Part 2.” Collectors Club Philatelist. Vol. XXVII, No. 3, p.45 – 50.
Other Resources:
- Brid, F. and Helme, J.B. “The Panama Issue of 1906 -07 Printed by the Hamilton Bank Note Co. of New York: The background of the issue and a listing of the die and plate proof varieties.” Copacarta. (September 1996), p. 8-25.
