| 1 | IOP | Caliop | | F | AVCODES |
| 2 | IOP | Caliop | Callsign: Caliop, | F | AVCODES |
| 3 | IOPU | CANTREYN, LTD | | | SCAC3 |
| 4 | IOPX | MidAmerican Energy Co. | added 4/1996; 7/2000-7/2005 | | NAKINA |
| 5 | IOPX | Midwest Power Systems | added 4/1993; 1/1994; eliminated 4/1996 | | NAKINA |
| 6 | IOPX | Iowa Power & Light Co. | added 4/1977; 1/1980; eliminated 4/1993 | | NAKINA |
| 7 | IOPX | Iowa Power & Light Co. | 1/80; eliminated 4/93 | | NRHS |
| 8 | IOPX | Midwest Power Systems | added 4/93; 1/94; eliminated 4/96 | | NRHS |
| 9 | IOPX | MidAmerican Energy Co. | added 4/96; 7/2000 | | NRHS |
| 10 | IOPX | MIDAMERICAN ENERGY CO [MIDWEST POWER SYSTEMS; IOWA POWER & LIGHT] | | | PWRC |
| 11 | IOPX | Iowa Power and Light (MidAmerican Energy) | | | RSRV |
| 12 | IOPZ | IOWA PUBLIC SERVICE | | | PWRC |
