140 joueurs et joueuses, classés par nom de famille. Chaque fiche donne le bilan depuis 2021, le détail par surface et l'historique des matchs.
| Joueur | Pays | Classement | Matchs depuis 2021 |
|---|---|---|---|
| Christopher O'Connell | Australia | — | 325 |
| Benjamin O'Connell | Australia | — | 100 |
| Osgar O'Hoisin | Ireland | — | 172 |
| Anamaria Federica Oana | Romania | — | 102 |
| Lucas Obeid | Brazil | — | 53 |
| Mia E'Halli Obeid | Argentina | — | 27 |
| Neil Oberleitner | Austria | — | 338 |
| Dusan Obradovic | Serbia | — | 319 |
| Andrea Obradovic | Serbia | — | 136 |
| Lun Obrul | Slovenia | — | 32 |
| Makoto Ochi | Japan | — | 250 |
| Svenja Ochsner | Switzerland | — | 34 |
| Julian Ocleppo | Italy | — | 101 |
| Caterina Odorizzi | Italy | — | 158 |
| Adrian Oetzbach | Germany | — | 401 |
| Maximilian Oezcelik | Germany | — | 51 |
| Sebastian Ofner | Austria | — | 311 |
| Haine Ogata | Japan | — | 96 |
| Simona Ogescu | Romania | — | 205 |
| Claudia Ogescu | Romania | — | 34 |
| Oluwaseun Peter Ogunsakin | Nigeria | — | 31 |
| Jaquelyn Ogunwale | Great Britain | — | 36 |
| Kosuke Ogura | Japan | — | 311 |
| Chan-Yeong Oh | Korea | — | 120 |
| Yugyeong Oh | Korea | — | 36 |
| Eunji Oh | Korea | — | 44 |
| Jiyun Oh | Korea | — | 27 |
| Yuna Ohashi | Japan | — | 77 |
| Remika Ohashi | Japan | — | 66 |
| Yui Ohwaki | Japan | — | 93 |
| Suzuna Oigawa | Japan | — | 34 |
| Oliver Ojakaar | Estonia | — | 74 |
| Martina Okalova | Slovakia | — | 191 |
| Kyoka Okamura | Japan | — | 332 |
| Issei Okamura | Japan | — | 162 |
| Yuto Oki | Japan | — | 98 |
| Oliver Okonkwo | Great Britain | — | 91 |
| Ramazan Kaan Oktay | Turkey | — | 25 |
| Alisa Oktiabreva | Czech Republic | — | 114 |
| Ayaka Okuno | Japan | — | 26 |
| Dilara Okur | Netherlands | — | 62 |
| Angella Okutoyi | Kenya | — | 136 |
| Rinon Okuwaki | Japan | — | 149 |
| Inigo Garmendia Olasagasti | Spain | — | 23 |
| Yshai Oliel | Israel | — | 263 |
| Sabrina Olimjanova | Uzbekistan | — | 62 |
| Maria Navarro Oliva | Mexico | — | 195 |
| Eric Jr. Olivarez | Philippines | — | 37 |
| Goncalo Oliveira | Portugal | — | 298 |
| Christian Oliveira | Brazil | — | 40 |
| Francisco Oliveira | Portugal | — | 41 |
| Emily De Oliveira | United States | — | 24 |
| Maria Luisa Oliveira | Brazil | — | 35 |
| Nicolas Oliveira | Brazil | — | 46 |
| Liam Oliver | United States | — | 37 |
| Albano Olivetti | France | — | 22 |
| Genaro Alberto Olivieri | Argentina | — | 343 |
| Renzo Olivo | Argentina | — | 280 |
| Nazar Oliynykov | Croatia | — | 78 |
| Oleksandra Oliynykova | Ukraine | — | 301 |
| Ane Mintegi Del Olmo | Spain | — | 174 |
| Giuliana Olmos | Mexico | — | 20 |
| Astrid Wanja Brune Olsen | Norway | — | 143 |
| Hephzibah Oluwadare | Great Britain | — | 49 |
| Valeriya Olyanovskaya | Russia | — | 148 |
| Akiko Omae | Japan | — | 133 |
| Amir Omarkhanov | Kazakhstan | — | 108 |
| Gauthier Onclin | Belgium | — | 402 |
| Klara Ondrejcekova | Slovakia | — | 32 |
| Paula Mihaela Onita | Romania | — | 20 |
| Luka Bojicic Ono | Brazil | — | 92 |
| Matei Cristian Onofrei | Romania | — | 108 |
| Yujiro Onuma | Great Britain | — | 80 |
| Erica Oosterhout | United States | — | 47 |
| Aleksa Oparnica | Serbia | — | 25 |
| Reilly Opelka | United States | — | 175 |
| Jannik Opitz | Germany | — | 115 |
| Patrik Oplustil | Czech Republic | — | 107 |
| Giovanni Oradini | Italy | — | 378 |
| Drew Van Orderlain | United States | — | 163 |
| Aleksander Orlikowski | Poland | — | 61 |
| Daniel Orlita | Czech Republic | — | 25 |
| Vladyslav Orlov | Ukraine | — | 391 |
| Alexander Orlov | Switzerland | — | 102 |
| Natalia Orlova | Russia | — | 77 |
| Paula Ormaechea | Argentina | — | 186 |
| Xavi Matas Ortega | Spain | — | 213 |
| Roberto Ortega-Olmedo | Spain | — | 44 |
| Jazmin Ortenzi | Argentina | — | 293 |
| Gian Marco Ortenzi | Italy | — | 212 |
| Benedetta Ortenzi | Italy | — | 132 |
| Oscar Gabriel Ortiz | Argentina | — | 20 |
| Islam Orynbasar | Kazakhstan | — | 35 |
| Adesuwa Osabuohien | United States | — | 30 |
| Kanako Osafune | Japan | — | 89 |
| Naomi Osaka | Japan | — | 182 |
| Zac Osborne | Australia | — | 24 |
| Alexandra Osborne | Australia | — | 164 |
| Suzuho Oshino | Japan | — | 27 |
| Vladimir Osminkin | Russia | — | 37 |
| Gillian Osmont | France | — | 40 |
| Aydan Gomez Osorio | Netherlands Antilles | — | 58 |
| Juan Sebastian Osorio | Colombia | — | 227 |
| Jakub Ostajewski | United States | — | 40 |
| Jelena Ostapenko | Latvia | — | 283 |
| Daniil Ostapenkov | Belarus | — | 247 |
| Sam Oster | Australia | — | 71 |
| Mavie Osterreicher | Austria | — | 148 |
| Fanny Ostlund | Sweden | — | 148 |
| Martyna Ostrzygalo | Canada | — | 21 |
| Whitney Osuigwe | United States | — | 302 |
| Victoria Osuigwe | United States | — | 108 |
| Jan Osusky | Slovakia | — | 28 |
| Ignacio Antonio Becerra Otarola | Chile | — | 123 |
| Juan Bautista Otegui | Argentina | — | 254 |
| Kentaro Otsuka | Japan | — | 29 |
| Oscar Otte | Germany | — | 185 |
| Jade Otway | New Zealand | — | 44 |
| Jana Otzipka | Belgium | — | 162 |
| Lamine Ouahab | Morocco | — | 21 |
| Aziz Ouakaa | Tunisia | — | 358 |
| Zineb El Ouazzani | Morocco | — | 26 |
| Guy Den Ouden | Netherlands | — | 300 |
| Mohamed Amin Oueslati | Tunisia | — | 50 |
| Rayane Oumaouche | France | — | 82 |
| Salakthip Ounmuang | Thailand | — | 82 |
| Hugo Ouzilou | Switzerland | — | 54 |
| Ekaterina Ovcharenko | Russia | — | 256 |
| Oleksandr Ovcharenko | Ukraine | — | 352 |
| Daniil Ovcharenko | Russia | — | 26 |
| Viacheslav Ovchinnikov | Russia | — | 91 |
| Carl Emil Overbeck | Denmark | — | 129 |
| Kyle Overmyer | United States | — | 134 |
| Ipek Oz | Turkey | — | 352 |
| S Mert Ozdemir | Turkey | — | 156 |
| Michika Ozeki | Japan | — | 249 |
| Ayaka Ozeki | Japan | — | 70 |
| Anna Ozerova | Latvia | — | 149 |
| Pemra Ozgen | Turkey | — | 194 |
| Karlis Ozolins | Latvia | — | 137 |