| Ocean Beach Amusement Park | Rhyl, Denbighshire, Wales, United Kingdom | - | | - |
| Ocean Playland | Ocean City, Maryland, United States | - | | - |
| Ocean View Amusement Park | Norfolk, Virginia, United States | - | - | - |
| Ocean World | Mueang Chonburi, Chon Buri, Thailand | - | | - |
| Odakyu Mukogaoka Yuen | Kawasaki, Kanagawa, Japan | - | | - |
| O.D. Pavilion Amusement Park | North Myrtle Beach, South Carolina, United States | - | | - |
| Okinawa Island Park | Okinawa, Okinawa, Japan | - | | - |
| Okpo Land | Okpo, Gyeongsangnam-do, South Korea | - | - | - |
| Old Chicago | Bolingbrook, Illinois, United States | - | | - |
| Old Indiana Fun-n-Water Park | Thorntown, Indiana, United States | - | | - |
| Olentangy Park | Columbus, Ohio, United States | - | | - |
| Olimpyc Park | Santo Domingo Este, Santo Domingo, Dominican Republic | - | | - |
| Olivieri Luna Park | Oliveri, Sicily, Italy | - | ≤ | - |
| Olympia Park | McKeesport, Pennsylvania, United States | - | - | - |
| Olympic Park | Irvington, New Jersey, United States | - | | - |
| Olympic Park | Rochester, New York, United States | - | | - |
| Omaezaki Land | Omaezaki, Shizuoka, Japan | - | - | - |
| Opryland USA | Nashville, Tennessee, United States | - | | - |
| Orange County Fairgrounds | Middletown, New York, United States | Operating | - | - |
| Oriental Park | Baiyun, Guangzhou, Guangdong, China | - | | - |
| Oriental Science Fiction Valley | Nanming, Guiyang, Guizhou, China | - | | - |
| Orient Culture Park | Xiaoshan, Hangzhou, Zhejiang, China | - | ≤ | - |
| Orumieh Park | Urmia, West Azerbaijan, Iran | - | ≤ | - |
| Ostdeutsche Austellung 1911 | Poznań, Wielkopolskie, Poland | - | | - |