| Title | Author |
|---|---|
| Old Faithful Inn, Yellowstone National Park | John Clayton |
| Old West Museum | |
| Opal Hub, The | |
| Oregon Basin Oil Field | Rebecca Hein |
| Oregon Buttes | |
| Oregon Buttes, Oregon Trail landmark | WyoHistory.org |
| Oregon Trail Ruts | |
| Oregon Trail Ruts | Wyoming State Historic Preservation Office |
| Oregon Trail-Ferdinand V. Hayden Monument | |
| Osborne, Gov. John E., and Wyoming politics, 1892-1893 | Lori Van Pelt |