| Ocean Spray | Lakeville | 1930 |
| Office Depot | Boca Raton | 1986 |
| Olin Corporation | Clayton | 1892 |
| Open Invention Network | Durham, Nueva York | 10 de noviembre de 2005 |
| OpenTable | San Francisco | 1998 |
| Orion Pictures | Los Ángeles | enero 1978 |
| Osborne Computer Corporation | Hayward | 27 de septiembre de 1979 |
| Oscar Mayer | Chicago | 1883 |
| Oshkosh Corporation | Oshkosh | 1917 |
| OTC Bulletin Board | Washington D. C. | — |
| Ovation Guitar Company | New Hartford | 1966 |
| Overland Automobile Company | Indianápolis | 1903 |
| Overstock.com | Midvale | 2023 |
| Owen illinois | Toledo, Perrysburg | 1903 |
| Palantir Technologies | Miami | 2003 |
| PalmSource | Reston | — |
| Panavision | Woodland Hills | 1953 |
| Parallels | Renton | 1999 |
| Paramount Animation | Los Ángeles | 2011 |
| Paramount Global | Nueva York, One Astor Plaza | 4 de diciembre de 2019 |
| Paramount Global Content Distribution | Santa Mónica, Nueva York | 1962 |
| Parker Pen Company | Newhaven, Londres | 1888 |
| Peavey | Meridian | 1965 |
| Peerless | Cleveland | 1900 |
| Pegasystems | Cambridge | 1983 |
| Penguin Random House | Nueva York | 1 de julio de 2013 |
| PeopleSoft | Pleasanton, California | 1987 |
| Perforce Zend | Minneapolis | 1999 |
| Petco | San Diego | 1965 |
| Phillips 66 | Westchase | 1 de mayo de 2012 |
| Phillips Petroleum Company | Bartlesville | 1917 |
| PhoenixEV | Ontario | 2002 |
| Pillsbury Company | Minneapolis | 1872 |
| PING | Phoenix | 1959 |
| Pinkberry | Los Ángeles | 2005 |
| Pioneer Hi-Bred | Johnston | 1926 |
| Plaxo | Sunnyvale | julio 2001 |
| Playboy Enterprises | Los Ángeles | 1953 |
| PNC Financial Services | One PNC Plaza | 1982 |
| Polycom | San José | 1990 |
| Powell Peralta | — | 1978 |
| Powell's Books | Portland | 1971 |
| PR Newswire | Manhattan | 8 de marzo de 1954 |
| Pratt & Whitney | East Hartford | 1925 |
| Pratt & Whitney Rocketdyne | Canoga Park | 2005 |
| Praxair | Danbury | 1907 |
| Prime Computer | Natick | 1972 |
| Prince Sports | Bordentown | 1970 |