The story of the Oregon Trail commemoratives is one of explotation and greed. The coins were struck in large quantities to begin with, i.e. the 1926, 1926-S, and 1928 issues, but after several years of trying to sell all 100,055 1926-S Oregons before the 1928 issue could be released, the dealers involved realized that a lower, obstensibly rarer issue would be easier to sell for a good profit and they convinced the Mint to melt 44,000 of the 50,028 originally minted of the 1928. After that the Oregons had lower mintages and were struck in 1933, 1934, 1936, 1937, 1938, and 1939. In other words, Oregons were struck from 1926 thru 1939. No other silver commemorative issue had an issue period that long
While the actual issue of the Oregon Trails was somewhat contrived, the design of the coins is very beautiful. Some people, myself included, consider them to be among the most beautiful U.S. coins ever made.
The 1926 Philadelphia was the first Oregon Trail commemorative struck. There were 47,955 distributed at an issue price of $1.00. Although both the 1926 and 1926-S Oregons had original mintages that were way higher (by many multiples) than later issues, they are just a little bit more common in MS65 condition and about as common in MS66 condition. Actually, the most common Oregons in MS66 condition are the three much lower mintage 1938 issues. But in MS63 and MS64 condition, the 1926 and 1926-S are much more common than the the later issues.
The 1926 is just slightly scarcer than the 1926-S in all grades. The typical 1926 Oregon has very frosty luster and most examples are relatively mark free. Strike is not usually a problem with the 1926, but it can be a problem with the 1926-S.