Politics and Business magazines
- Old Town Canoe Company
- Olga's Kitchen, Inc.
- Olivetti S.p.A.
- Omaha Steaks International Inc
- OMI Corporation
- Omni Hotels Corp.
- Omnicare, Inc.
- Omnicell, Inc.
- OmniSource Corporation
- OMNOVA Solutions Inc.
- Omron Corporation
- Omron Tateisi Electronics Company
- ÖMV Aktiengesellschaft
- On Assignment, Inc.
- One Price Clothing Stores, Inc.
- ONEOK Inc.
- Onion, Inc.
- Onoda Cement Co., Ltd.
- Ontario Hydro
- Ontario Hydro Services Company