| OND 2168301 · TMA1272519 | Oxford Nanopore Technologies Limited | 1 Chemicals5 Pharmaceuticals9 Electronics+5 | Registered | 2024 |
| OMD 2056648 | TeleSense Canada Inc. | 9 Electronics37 Construction42 Science+1 | Pending | 2020 |
| OMD 0972086 | Owner not shown | 1 Chemicals2 Paints3 Cosmetics+42 | Pending | 2006 |
| ONUDI 0972476 | Owner not shown | 1 Chemicals2 Paints3 Cosmetics+42 | Pending | 2010 |
| ONUDI 0972473 · design | Owner not shown | 1 Chemicals2 Paints3 Cosmetics+42 | Pending | 2010 |
| ONUDI 0972472 · design | Owner not shown | 1 Chemicals2 Paints3 Cosmetics+42 | Pending | 2010 |
| Onmiwod 2301525 · design | DongGuanShi Honglidianzikeji Co. Ltd | 15 Musical | Pending | 2023 |
| Omiodo 2261044 · TMA1279551 | Shenzhen Yuke Electronics Co. Ltd. | 7 Machines9 Electronics | Registered | 2024 |
| ONWOOD 2176732 · TMA1227124 | T2Earth Holdings LLC | 19 Building | Registered | 2024 |
| ONDA 2164726 · TMA1213342 | Apollo Healthcare Corp. | 3 Cosmetics | Registered | 2023 |
| ONTO 2147834 · TMA1257693 | Onto Innovation Inc. | 7 Machines9 Electronics42 Science | Registered | 2024 |
| oentyo 2071189 · TMA1161330 | Yiwu Shengxu Jewelry Co. Ltd. | 24 Textiles | Registered | 2023 |
| ONE8TH 2065472 · TMA1221091 | FAN INK LIMITED | 25 Clothing | Registered | 2024 |
| OMADA 2053505 · TMA1187092 · design | an individual | 21 Housewares | Registered | 2023 |
| ONEIDA 2016126 · TMA1212788 · combined | ONEIDA CONSUMER, LLC | 8 Hand | Registered | 2023 |
| ONEIDA 2016125 · TMA1212787 · combined | ONEIDA CONSUMER, LLC | 8 Hand | Registered | 2023 |
| ONTEEO 2011573 · TMA1191421 | Fresenius Kabi Deutschland GmbH | 5 Pharmaceuticals | Registered | 2023 |
| ONWOTE 1981073 · TMA1134605 · design | Shenzhen Onwote Smart Technology Co.Ltd | 9 Electronics | Registered | 2022 |
| ONNIT 1976328 · TMA1170607 · design | Onnit Labs, Inc. | 5 Pharmaceuticals | Registered | 2023 |
| ONATA 1964923 · TMA1135372 | an individual | 7 Machines9 Electronics11 Lighting+4 | Registered | 2022 |
| ONEDAYAWAY 1916827 · TMA1109118 · design | Shanghai Shenda (America), LLC | 25 Clothing | Registered | 2021 |
| Omneity 1850109 · TMA1018496 | Mad Barn Inc | 5 Pharmaceuticals | Registered | 2019 |
| OWNAT 1815857 · TMA1068371 | an individual | 31 Fresh | Registered | 2020 |
| ONDUO 1786133 · TMA1028119 | Onduo LLC | 9 Electronics10 Medical38 Telecommunications+2 | Registered | 2019 |
| ONMETIO 1723278 · TMA1041110 | OTSUKA PHARMACEUTICAL CO. LTD. | 5 Pharmaceuticals | Registered | 2019 |