| 1 | UFI | Umbria Fly | Callsign: Umbria Fly, | I | AVCODES |
| 2 | UFIC | US FREIGHTWAYS INC | | | SCAC4 |
| 3 | UFIX | Utility Fuels, Inc. | added 7/1978; 1/1980-1/1994; eliminated 4/1994 | | NAKINA |
| 4 | UFIX | Houston Lighting & Power Co. | added 4/1994; eliminated 7/2000 | | NAKINA |
| 5 | UFIX | Reliant Energy HL&P | added 7/2000; 7/2000; eliminated 10/2004 | | NAKINA |
| 6 | UFIX | Texas Genco, LP | added 10/2004; eliminated 7/2005 | | NAKINA |
| 7 | UFIX | Texas Genco II, LP | added 7/2005; 7/2005; eliminated 10/2006 | | NAKINA |
| 8 | UFIX | NRG Energy, Inc. | added 10/2006; eliminated 4/2009; eliminated 7/2009 | | NAKINA |
| 9 | UFIX | Utility Fuels, Inc. | added 7/78; 1/80-1/94; eliminated 4/94 | | NRHS |
| 10 | UFIX | Houston Lighting & Power Co. | added 4/94; eliminated 7/2000 | | NRHS |
| 11 | UFIX | Reliant Energy HL&P | added 7/2000; 7/2000 | | NRHS |
| 12 | UFIX | *UTILITY FUELS INC. | | | PWRC |
| 13 | UFIX | +NRG ENERGY, INC. [TEXAS GENCO; [RELIANT ENERGY; HOUSTON LIGHTING & POWER COMPANY] | | | PWRC |
| 14 | UFIX | Utility Fuels | | | RSRV |
| 15 | UFIX | NRG ENERGY INC | | | SCAC4 |
| 16 | UFIZ | U.F.I. CORP | | | PWRC |
