| Abbreviation | Definition |
|---|---|
| OIDC | Omnibus Industrial Development Corporation |
| OIEC | Obaidly ISCO Engineering Company |
| OIFC | Ocean Isle Fish Company |
| OIFL | Owen Industrial Filtration, Ltd |
| OIG | Orbital Information Group |
| OII | Oceaneering International Inc |
| OII | Ohio's Insurance Industry |
| OII | Ophthalmic Innovations International |
| OIK | Oppenheim Immobilien-Kapitalanlagegesellschaft GmbH (German: Oppenheim Real Estate Investment Company; Oppenheim, Germany) |
| OIK | Ornamental Iron of Kalamazoo (Kalamazoo, Michigan) |
| OIL | Oil India Ltd |
| OILC | Ontario Infrastructure and Lands Corporation |
| OILC | Ontario Infrastructure Lands Corporation |
| OIN | Online Investor Network |
| OINS | Oriental Intelligentsia Nurturing Services |
| OIPI | Ouray Ice Park Inc |
| OIR | Optima Investment Research |
| OIRLLC | Okaloosa Island Restoration Limited Liability Company |
| OIS | O'Brien Investment Services |
| OIS | OMNI Information Services |