| O'Fallon John | U.S. Department of Energy | USA |
| Oakes Robert | Northwestern University | USA |
| Oh Choo-Hiap | National University of Singapore | Singapore |
| Oh Sun Kun | Konkuk University | Korea |
| Ohska Tokio | KEK | Japan |
| Olness Fredrick | Southern Methodist University | USA |
| Olsen James | Princeton University | USA |
| Ootani Wataru | ICEPP, University of Tokyo | Japan |
| Orava Risto | University of Helsinki & Helsinki Institute of Physics | Finland |
| Orejudos William Gilbert | Lawrence Berkeley National Laboratory | USA |
| Oshima Nobu | Fermi National Accelerator Laboratory | USA |
| Owens Jeff | Florida State University | USA |