An odds-on favorite is one that's less than even money. Going back to 1890, the first year the Preakness race charts list each horse's odds, here are the odds-on favorites and how they fared.
Year Horse Odds to dollar Fin. Winner
1989 Easy Goer .60 2nd Sunday Silence
1984 Swale .80 7th Gate Dancer
1982 Linkage .50 2nd Aloma's Ruler
1979 Spectacular
Bid. .10 1st Spectacular Bid
1978 Affirmed .50 1st Affirmed
1977 Seattle Slew .40 1st Seattle Slew
1976 Honest
Pleasure .90 5th Elocutionist
1973 Secretariat .30 1st Secretariat
1972 Riva Ridge .30 4th Bee Bee Bee
1969 Majestic Prince.60 1st Majestic Prince
1964 Hill Rise .80 3rd Northern Dancer
1956 Needles .60 2nd Fabius
1955 Nashua .30 1st Nashua
1954 Correlation .90 2nd Hasty Road
1953 Native Dancer .20 1st Native Dancer
1950 Hill Prince .70 1st Hill Prince
1948 Citation .10 1st Citation
1943 Count Fleet .15 1st Count Fleet
1940 Bimelech .90 1st Bimelech
1939 Gilded Knight .45 2nd Challedon
1937 War Admiral .35 1st War Admiral
1935 Omaha .95 1st Omaha
1934 High Quest .45 1st High Quest
1920 Man o' War .80 1st Man o' War
1918 Jack Hare Jr. .90 1st Jack Hare Jr.
Note: In 1918 Jack Hare Jr. and War Cloud finished in a dead heat.