| OMNIJET 1195913 · TMA678675 | Ilford Imaging Europe GmbH | 16 Paper | Registered | 2006 |
| ONESAT 2170045 · TMA1204341 | Owner not shown | 9 Electronics | Registered | 2023 |
| ONSET 1924133 · TMA1102441 | Tulsar Canada Ltd. | 9 Electronics | Registered | 2021 |
| ONSET 1763840 · TMA999063 | 1623774 Ontario Inc. dba Titan Distribution | 5 Pharmaceuticals | Registered | 2018 |
| ONSET 1519061 · TMA870434 · design | an individual | 9 Electronics | Registered | 2014 |
| ONSET 1418709 · TMA772750 | an individual | 9 Electronics | Registered | 2010 |
| ONEKIT 2130454 | O'Neil Digital Solutions, LLC (a California limited liability company) | 42 Science | Pending | 2021 |
| ONEKIT 2130452 · design | O'Neil Digital Solutions, LLC (a California limited liability company) | 42 Science | Pending | 2021 |
| ONESTEM 1942613 · TMA1123998 | Mark L. Anderson and BioDivide Limited, a partnership | 5 Pharmaceuticals | Registered | 2022 |
| ONESTEP 1905392 · TMA1086943 · design | Interplastic Corporation | 1 Chemicals | Registered | 2020 |
| ONESTEP 1723049 · TMA944946 | TOPS Products LLC | 16 Paper | Registered | 2016 |
| OMNISET 1680917 · TMA1063253 | an individual | 10 Medical | Registered | 2019 |
| ONESTER 1663653 · TMA901337 | Munchkin, Inc. | 25 Clothing | Registered | 2015 |
| ONYXWET 1647069 · TMA892849 | Blackstone Drilling Fluids Limited | 1 Chemicals | Registered | 2014 |
| ONESUIT 1273706 · TMA715975 | Saint-Gobain Performance Plastics Corporation | 9 Electronics | Registered | 2008 |
| ONESTEP 0494188 · TMA297482 · design | TOPS Products LLC | 16 Paper | Registered | 1984 |
| ONESTEP 0410383 · TMA234294 | POLAROID CORPORATION | 9 Electronics | Registered | 1979 |
| ONCOTERRA 2217074 · TMA1235265 | Phase Genomics, Inc. | 42 Science | Registered | 2024 |
| OMGTMD 2177941 · TMA1227273 | an individual | 6 Metal | Registered | 2024 |
| OneStock 2177427 · TMA1278840 | OneStock | 42 Science | Registered | 2024 |
| ONSTIN 2137448 · TMA1220442 | NUTRA STANDARD INC | 5 Pharmaceuticals | Registered | 2024 |
| ownest 2133469 · TMA1196912 | Guangzhou Yunhan Xiangfeng Network Technology Co. Ltd. | 9 Electronics | Registered | 2023 |
| OnkoDisruptor 2129418 · TMA1195788 | an individual | 10 Medical | Registered | 2023 |
| ONESTREAM 2114513 · TMA1228780 | OneStream Software LLC | 9 Electronics35 Advertising41 Education+1 | Registered | 2024 |
| OMIGHTY 2108361 · TMA1139904 · design | FOKDA POPO PTE LTD | 18 Leather25 Clothing35 Advertising | Registered | 2022 |