The standard reference work for Saudi Arabian revenue stamps is A Catalogue of the
Fiscal Stamps of Saudi Arabia 1916-2001 by R. J. Thoden (Rudy). The author was always
aware that the catalogue was incomplete and I include on this site information to
augment the catalogue. A task for the future will be to produce an updated version
of the manual; I am sure that Rudy would not wish interest in the subject to dimish.