Politics and Business magazines
- Ohio Bell Telephone Company
- Ohio Casualty Corp.
- Ohio Edison Company
- Oil and Natural Gas Commission
- Oil and Natural Gas Corporation Ltd.
- Oil States International, Inc.
- OJSC Wimm-Bill-Dann Foods
- Oki Electric Industry Company, Limited
- Oklahoma Gas and Electric Company
- Okuma Holdings Inc.
- Okura & Co., Ltd.
- Olan Mills, Inc
- Old America Stores, Inc.
- Old Dominion Freight Line, Inc.
- Old Kent Financial Corp.
- Old Mutual PLC
- Old National Bancorp
- Old Navy, Inc.
- Old Orchard Brands, LLC
- Old Spaghetti Factory International Inc.