| Oregon State T.B. Hospital | Salem | OR |
| Oregon Steel Foundry | Portland | OR |
| Oregon Steel Mills | Portland | OR |
| Oregon Sugar | La Grande | OR |
| Oregon Technical Institute | Klamath Falls | OR |
| Oregon Trail | Portland | OR |
| Oregon Utah Sugar | Grants Pass | OR |
| Oregon-Washington Railroad & Navigation | Huntington | OR |
| Oriental Ace | Portland | OR |
| Oriental Arrow | Portland | OR |
| Otto Castrow | Portland | OR |
| Overseas Progress | Portland | OR |
| Owens Corning | Portland | OR |
| Owens Illinois | Portland | OR |
| Owen Summers | Portland | OR |
| Owyhee | Portland | OR |
| Paceagle | Portland | OR |
| Pacific Carbide & Alloys | Portland | OR |
| Pacific Coast Biscuit | Portland | OR |
| Pacific Hdw & Steel | Portland | OR |
| Pacific Northwest Bell | Independence | OR |
| Pacific Power & Light | Portland | OR |
| Pacific Power & Light | Astoria | OR |
| Pacific University | Forest Grove | OR |
| Pacrobin | Portland | OR |
| Pactrader | Portland | OR |
| Panaman | Portland | OR |
| Parkrose Water District | Portland | OR |
| Patricia D. | Portland | OR |
| Pauline | Portland | OR |
| Paulus Brothers Packing | Salem | OR |
| Payless Drug Store | Portland | OR |
| Pecos | Portland | OR |
| Pelican State Lime | Portland | OR |
| Pendleton | Portland | OR |
| Pendleton Woolen Mills | Pendleton | OR |
| Pendleton Woolen Mills | Portland | OR |
| Pennisula Lumber | Portland | OR |
| Penn Sailor | Portland | OR |
| Pennsylvania | Portland | OR |
| Pennsylvania Salt Manufacturing | Portland | OR |
| Pennsylvania Salt Manufacturing | Salem | OR |
| Pennwalt | Portland | OR |
| Penn Walt Chemicals | Portland | OR |
| Pequot Hill | Portland | OR |
| Permanente Silverbow | Portland | OR |
| Petmeteo | Portland | OR |
| Petrakis Nomikos Iii | Portland | OR |
| Petronorte | Portland | OR |
| Petros | Portland | OR |
