| 1 | IPSX | General American Marks Co. | added 1/2003; 7/2005 | | NAKINA |
| 2 | IPSX | GATX Financial Corp. | added 1/2002; eliminated 1/2003 | | NAKINA |
| 3 | IPSX | GATX Capital Corp. | added 4/1999; 7/2000; eliminated 1/2002 | | NAKINA |
| 4 | IPSX | MidAmerican Energy Co. | added 4/1996; eliminated 4/1999 | | NAKINA |
| 5 | IPSX | Midwest Power Systems | added 1/1994; eliminated 4/1996 | | NAKINA |
| 6 | IPSX | Midwest Energy Services Co. | added 7/1983 | | NAKINA |
| 7 | IPSX | Midwest Energy Service Co. | added 5/1983; eliminated 7/1983 | | NAKINA |
| 8 | IPSX | Energy Development Co. | added 7/1972; 1/1975-1/1980; eliminated 5/1983 | | NAKINA |
| 9 | IPSX | Energy Development Co. | 1/75-1/80; eliminated 5/83 | | NRHS |
| 10 | IPSX | Midwest Energy Service Co. | added 5/83 | | NRHS |
| 11 | IPSX | Midwest Power Systems | added 1/94; eliminated 4/96 | | NRHS |
| 12 | IPSX | MidAmerican Energy Co. | added 4/96; eliminated 4/99 | | NRHS |
| 13 | IPSX | GATX Capital Corp. | added 4/99; 7/2000 | | NRHS |
| 14 | IPSX | GENERAL AMERICAN MARKS CO., MIDAMERICAN ENERGY CO (IOPX) LESSEE [MIDWEST POWER SYSTEMS] | | | PWRC |
| 15 | IPSX | Midwest Energy Services (GATX) | | | RSRV |
| 16 | IPSX | GENERAL AMERICAN MARKS COMPANY | | | SCAC4 |
