The United States 1898 Trans-Mississippi commemoratives have always been popular with collectors. On April 28, 2001, Schuyler Rumsey Philatelic Auctions of San Francisco sold an earliest-known-use (EKU) cover of a $2 Trans-Mississippi stamp for a record breaking $55,000. It was from a collection formed over 50 years by a retired psychiatry professor.

The issued date of the stamp is recorded in catalogues as June 17, 1898. Prior to the discovery of this cover, the other earliest-known-use is a cover bearing the complete set of stamps mailed on July 18, 1898 from New York City to Germany.

Other covers bearing single examples of the rest of the set; 1¢, 2¢, 4¢, 5¢, 8¢, 10¢, 50¢ and $1, all mailed on the same date in Philadelphia on the same afternoon have been discovered much earlier.