| 1 | PSO | Aerotaxis Pegaso, S.A. De C.V. | Callsign: Aeropegaso, | MEX | AVCODES |
| 2 | PSO | REPUBLIC STEEL (OHIO) | | | PWRC |
| 3 | PSOA | PAS OF ALABAMA INC | | | SCAC3 |
| 4 | PSOC | PURSER OIL CO INC | | | SCAC4 |
| 5 | PSOE | PORTABLE STORAGE OFFICE & EQUIPMENT | | | SCAC3 |
| 6 | PSOH | PETTYJOHN & SONS | | | SCAC4 |
| 7 | PSOI | PASCO INC | | | SCAC3 |
| 8 | PSOI | PASCO INC | | | SCAC4 |
| 9 | PSOL | PRESTO LINEA INC. | | | SCAC3 |
| 10 | PSOM | PANSOLAR SPECIAL MARITIME ENTERPRIS | | | SCAC4 |
| 11 | PSON | PRODIGALSON VENTURES INC | | | SCAC4 |
| 12 | PSOQ | PASO ROBLE VAN & STORAGE | | | SCAC3 |
| 13 | PSOS | PATTERSON, MISHELLE SMITH | | | SCAC4 |
| 14 | PSOT | PRECISION TRANSPORT | | | SCAC3 |
| 15 | PSOU | PENTALVER TRANSPORT LIMITED | | GB | BIC |
| 16 | PSOX | Puget Sound Power & Light Co. | added 1/1970; 4/1970-7/2000; eliminated 7/2002; 7/2005 (not listed) | | NAKINA |
| 17 | PSOX | Peerless Oil & Refining Co. | 7/1930 | | NAKINA |
| 18 | PSOX | Puget Sound Power & Light Co. | added 1/70; 4/70-7/2000 | | NRHS |
| 19 | PSOX | *PEERLESS OIL & REFINING CO. | | | PWRC |
| 20 | PSOX | *PUGET SOUND POWER & LIGHT CO. | | | PWRC |
| 21 | PSOX | Puget Sound Power and Light | | | RSRV |
| 22 | PSOZ | PUBLIC SERVICE OF OKLAHOMA | | | PWRC |
