| OMNISCAN 1163808 · TMA629574 | Olympus NDT Canada inc. | 9 Electronics | Registered | 2005 |
| OMNISCAN 0694296 · TMA421687 | an individual | 5 Pharmaceuticals | Registered | 1993 |
| OMZIN 1907224 · TMA1100645 · design | an individual | 25 Clothing | Registered | 2021 |
| OMNICAM 1590659 · TMA900754 | Sirona Dental Systems GmbH | 10 Medical42 Science44 Medical | Registered | 2015 |
| Onchain 2362261 | an individual | 36 Finance | Pending | 2024 |
| OMNISAN 2194122 · design | OmniLyte Enviro Inc. | 1 Chemicals3 Cosmetics5 Pharmaceuticals+2 | Pending | 2022 |
| OMNISAN 2113493 | OmniLyte Enviro Inc. | 1 Chemicals5 Pharmaceuticals11 Lighting+3 | 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 |
| 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 |
| 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 |
| ONEAGENT 2141675 · TMA1250808 | Dynatrace LLC | 9 Electronics | Registered | 2024 |
| OneCem 2134167 · TMA1240962 | Holcim Technology Ltd | 19 Building | Registered | 2024 |
| 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 |
| ONSON 2032896 · TMA1139663 | Shenzhen Weizhisheng E-Commerce Co.Ltd. | 7 Machines | Registered | 2022 |
| ONESING 2020998 · TMA1157956 | Shenzhen Suruiketa Technology Co. Ltd | 25 Clothing | Registered | 2022 |
| ONSON 2003667 · TMA1143464 · design | Shenzhen Weizhisheng E-Commerce Co.Ltd. | 7 Machines | 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 |