| ONCOMFORT 2058458 | an individual | 9 Electronics42 Science | Pending | 2020 |
| ONCOONE 2003628 · TMA1127198 | OncoOne Research & Development GmbH | 5 Pharmaceuticals42 Science44 Medical | Registered | 2022 |
| ONCOMINE 1989529 · TMA1098169 | Life Technologies Corporation | 42 Science | Registered | 2021 |
| ONCOMINE 1988537 · TMA1108109 | Life Technologies Corporation | 5 Pharmaceuticals | Registered | 2021 |
| ONCOMINE 1987115 · TMA1108090 | Life Technologies Corporation | 1 Chemicals | Registered | 2021 |
| ONCOMATE 1910693 · TMA1086892 | PROMEGA CORPORATION | 9 Electronics | Registered | 2020 |
| ONEXONE 1357631 · TMA772818 | ONEXONE Foundation | 14 Jewellery25 Clothing | Registered | 2010 |
| ONEXONE 1351887 · TMA717690 · design | ONEXONE Foundation | 35 Advertising | Registered | 2008 |
| ONEXONE 1260745 · TMA664818 | ONEXONE Foundation | 35 Advertising | Registered | 2006 |
| ONCENTRA 1246920 · TMA687609 | an individual | 9 Electronics10 Medical37 Construction+1 | Registered | 2007 |
| ONCENTRA 1106171 · TMA645602 · design | an individual | 9 Electronics | Registered | 2005 |
| ONEZONE 2272756 | SPEC FURNITURE INC. | 6 Metal19 Building20 Furniture+4 | Pending | 2023 |
| ONEZONE 2060213 | Global Resources International, Inc. | 10 Medical | Pending | 2020 |
| OMEGAMORE 1629689 · TMA957564 | Enerex Botanicals Ltd. | 5 Pharmaceuticals | Registered | 2016 |
| ONCIMMUNE 1421632 · TMA883677 | ONCIMMUNE HOLDINGS PLC, a legal entity | 10 Medical44 Medical | Registered | 2014 |
| 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 |
| ONESMART 1906120 · TMA1096234 | Shanghai Jingxuerui Information Science and Technology Co. Ltd. | 41 Education | Registered | 2021 |
| ONESMART 1879747 · TMA1096232 · design | Shanghai Jingxuerui Information Science and Technology Co. Ltd. | 41 Education | Registered | 2021 |
| ONGEMTA 1869294 · TMA1063540 | Owner not shown | 5 Pharmaceuticals | Registered | 2019 |
| ONCEMOREWITHLOVE 1847385 · TMA1076111 | OnceMoreWithLove Designs Inc. | 8 Hand9 Electronics11 Lighting+6 | Registered | 2020 |
| OMEZONE 1456223 · TMA790144 | AKM Services International Limited | 5 Pharmaceuticals | Registered | 2011 |
| ONGAME 1230116 · TMA746753 | Ongame Network Ltd. | 9 Electronics35 Advertising38 Telecommunications+3 | Registered | 2009 |
| ONCMD 0598730 · TMA350101 · design | ON-LINE DATA CORPORATION | 9 Electronics | Registered | 1989 |