| OWNSCENTS 2247545 | Owner not listed | 3 Cosmetics4 Oils | Pending | 2023 |
| ONSEN 1954250 · TMA1192262 · design | NuEnergy Distribution Inc. | 11 Lighting | Registered | 2023 |
| ONEAGENT 2141675 · TMA1250808 | Dynatrace LLC | 9 Electronics | Registered | 2024 |
| ONCENTRA 1246920 · TMA687609 | an individual | 9 Electronics10 Medical37 Construction+1 | Registered | 2007 |
| ONCENTRA 1106171 · TMA645602 · design | an individual | 9 Electronics | Registered | 2005 |
| ONECONTENT 1955730 · TMA1267664 | HYLAND SOFTWARE, INC. | 9 Electronics42 Science | Registered | 2024 |
| ONSEMI 2163807 · TMA1197147 · design | SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC | 9 Electronics40 Treatment42 Science | Registered | 2023 |
| ONSEMI 2162326 · TMA1196045 | SEMICONDUCTOR COMPONENTS INDUSTRIES, LLC | 9 Electronics40 Treatment42 Science | Registered | 2023 |
| OneCem 2134167 · TMA1240962 | Holcim Technology Ltd | 19 Building | Registered | 2024 |
| ONSON 2032896 · TMA1139663 | Shenzhen Weizhisheng E-Commerce Co.Ltd. | 7 Machines | Registered | 2022 |
| ONSON 2003667 · TMA1143464 · design | Shenzhen Weizhisheng E-Commerce Co.Ltd. | 7 Machines | Registered | 2022 |
| ONYXEN 1714004 · TMA950207 | an individual | 1 Chemicals | Registered | 2016 |
| ONOCON 2095727 · design | Onocon Developments Ltd. | 36 Finance37 Construction39 Transport+1 | Pending | 2021 |
| OMEGAMAZING 2212477 · TMA1243116 | Vibrant Health Products Inc. dba Silver Hills Bakery | 30 Coffee35 Advertising43 Restaurants | Registered | 2024 |
| Omzanclo 2188197 · TMA1282711 | CELLTRION, INC. | 5 Pharmaceuticals | Registered | 2025 |
| OMNISMART 2146610 · TMA1187769 | HONEYWELL INTERNATIONAL INC. | 9 Electronics | Registered | 2023 |
| OMEGANOMIX 2142609 · TMA1200382 | an individual | 20 Furniture | Registered | 2023 |
| OMEGANOMIC 2142608 · TMA1200381 | an individual | 20 Furniture | Registered | 2023 |
| OWANQIANG 2131450 · TMA1194321 | Shenzhen Heliliang Electronic Commerce Co. Ltd. | 11 Lighting | Registered | 2023 |
| ONSUMCO 2116225 · TMA1183023 | an individual | 5 Pharmaceuticals | Registered | 2023 |
| OMWEEKEND 2101656 · TMA1155469 · design | FOKDA POPO PTE LTD | 35 Advertising | Registered | 2022 |
| OMOZEN 2050879 · TMA1167986 · design | an individual | 21 Housewares | Registered | 2023 |
| ONESING 2020998 · TMA1157956 | Shenzhen Suruiketa Technology Co. Ltd | 25 Clothing | Registered | 2022 |
| ONCOONE 2003628 · TMA1127198 | OncoOne Research & Development GmbH | 5 Pharmaceuticals42 Science44 Medical | Registered | 2022 |
| ONCOMINE 1989529 · TMA1098169 | Life Technologies Corporation | 42 Science | Registered | 2021 |