| Original Film | film production company | Los Angeles | 1997 |
| Orion Pictures | film production company, business | Los Angeles | January 1978 |
| Osborne Computer Corporation | business | Hayward | September 27, 1979 |
| Oscar Mayer | business | Chicago | 1883 |
| Oshkosh Corporation | business, enterprise, public company | Oshkosh | 1917 |
| Overbrook Entertainment | business | Beverly Hills, Los Angeles | 1998 |
| P. F. Chang's China Bistro | restaurant chain | — | 1993 |
| P.A. Semi | business | Santa Clara | 2003 |
| Pace University | private not-for-profit educational institution, university | New York City | 1906 |
| Pacific Data Images | business | Redwood City | 1980 |
| Pacific Southwest Airlines | airline | San Diego, California | 1949 |
| Packard Bell | technology company, brand, business, enterprise | Chatsworth | 1926 |
| Padlet | business, enterprise | San Francisco | December 1, 2012 |
| Palace Hotel | hotel | — | 1875 |
| Palantir Technologies | defense contractor, business, enterprise, public company | Miami | 2003 |
| Palm, Inc. | business, enterprise | Sunnyvale | 1992 |
| Palms Casino Resort | skyscraper, casino, resort | — | 2001 |
| Palo Alto Research Center | business | Palo Alto | 1970 |
| Pan Am | airline, business | New York City | March 14, 1927 |
| Pan American Health Organization | open-access publisher, international organization | Washington, D.C. | December 2, 1902 |
| Pandora | music streaming service, website, organization, recommender system, online music database, public company | Oakland | January 2000 |
| Panera Bread | restaurant chain, public company | Sunset Hills | 1987 |
| Panic | video game publisher, video game developer, business | Portland, Oregon | — |
| Pantene | brand, business | Switzerland | 1945 |
| Pantone | business, enterprise | Carlstadt | 1962 |
| Parallels | business, enterprise | Renton | 1999 |
| Paramount Global Content Distribution | business | Santa Monica, New York City | 1962 |
| Paramount Home Entertainment | film distributor, subsidiary company | Hollywood | 1975 |
| Paris Las Vegas | casino, hotel | — | September 1, 1999 |
| Parker Brothers | video game publisher, video game developer, board game publishing company, brand, business | Beverly, Salem | 1883 |
| Peabody Energy | business, enterprise, public company | St. Louis | 1883 |
| Peabody Institute | conservatory, school | Baltimore | 1857 |
| Peavey Electronics | business, enterprise | Meridian | 1965 |
| Pegasystems | business, public company | Cambridge | 1983 |
| Pei Wei Asian Diner | restaurant | Scottsdale | 2000 |
| PenAir | airline | Anchorage | 1955 |
| Pennsylvania Hospital | hospital, teaching hospital | — | May 11, 1751 |
| Pennsylvania State University | public research university | Penn State University Park | February 22, 1855 |
| Pennzoil | business, enterprise | Houston | 1963 |
| Penske Media Corporation | media company, business | Los Angeles | 2004 |
| Pentaho | business, software | Orlando | 2004 |
| People Incorporated | holding company, business, enterprise, public company | New York City | July 28, 1986 |
| Perdue Farms | business | Salisbury | 1920 |
| Perforce Zend | brand, business, enterprise | Minneapolis | 1999 |
| Perplexity AI | artificial intelligence website, organization, business | San Francisco | December 7, 2022 |
| Perry–Castañeda Library | academic library | — | 1977 |
| Perseus Digital Library | digital library | — | 1987 |
| Petroglyph Games | video game publisher, video game developer | Las Vegas | April 1, 2003 |