| Oakland Arena | Oakland | 19,596 seats | November 9, 1966 |
| Oakland Ballpark | San Jose, Oakland | 32,000 seats | — |
| Odde Ice Center | — | 1,600 seats | 1980 |
| Ohio Stadium | Columbus | 104,944 seats | October 7, 1922 |
| Oklahoma State Fair Arena | Oklahoma City | 10,944 seats | 1965 |
| Omaha Civic Auditorium | Nebraska, Omaha, Douglas County | 10,960 seats | 1954 |
| Omni Coliseum | Atlanta | 16,181 seats | October 14, 1972 |
| Oncenter War Memorial Arena | Syracuse | 8,000 seats | September 12, 1951 |
| Oracle Park | San Francisco | 41,915 seats | April 11, 2000 |
| Oriole Park at Camden Yards | Baltimore | 48,876 seats | April 6, 1992 |
| OU Softball Complex | Norman | 1,378 seats | 1998 |
| Oval Lingotto | Turin | 8,500 seats | 2005 |