Politics and Business magazines
- Outokumpu Oyj
- Outrigger Enterprises, Inc.
- Overhead Door Corporation
- Overhill Corporation
- Overnite Corporation
- Overnite Transportation Co.
- Overseas Shipholding Group, Inc.
- Overstock.com, Inc.
- Owens Corning Corporation
- Owens-Corning Fiberglas Corporation
- Owosso Corporation
- Oxfam GB
- Oxford Health Plans, Inc.
- O’Melveny & Myers
- O’Sullivan Industries Holdings, Inc.
- P & F Industries, Inc.
- P&C Foods Inc.
- P.C. Richard & Son Corp.
- P.H. Glatfelter Company
- Pacer International, Inc.