| 1 | UP | Bahamasair | ICAO: BHS, Callsign: Bahamas, IATA Prefix: 111, Designator UP recall by IATA | BS | AVCODES |
| 2 | UP | Bahamasair | ICAO: BHS, Callsign: Bahamas, IATA Prefix: 111, Name changed to Bahamasair Holdings Limited. Designator UP reinstated by IATA | BS | AVCODES |
| 3 | UP | Air Foyle Limited | ICAO: UPA, Callsign: Foyle, IATA designator changed to GS | GB | AVCODES |
| 4 | UP | Bahamasair Holdings Limited | ICAO: BHS, Callsign: Bahamas, IATA Prefix: 111, Name changed from Bahamasair. Designator UP reinstated by IATA | BS | AVCODES |
| 5 | UP | Union Pacific R.R. Co. | 4/1961-7/2005 | | NAKINA |
| 6 | UP | Union Pacific R.R. Co. | 4/61-7/2000 | | NRHS |
| 7 | UP | UNION PACIFIC RAILROAD COMPANY | | | PWRC |
| 8 | UP | Union Pacific Railroad | | | RSRV |
| 9 | UP | UNION PACIFIC RAILROAD COMPANY | | | SCAC4 |
| 10 | UP | Union Pacific | | USA | TRAFFIC |
| 11 | UPA | Air Foyle Limited | IATA: GS, Callsign: Foyle, Designator recalled by IATA | GB | AVCODES |
| 12 | UPA | Air Foyle Limited | IATA: UP, Callsign: Foyle, IATA designator changed to GS | GB | AVCODES |
| 13 | UPA | Air Foyle Limited | Callsign: Foyle, Ceased operations. Designator recalled by IATA | GB | AVCODES |
| 14 | UPA | Air Foyle | IATA: GS | | ICAO1 |
| 15 | UPAC | UNITED PARCEL SERVICE COMPANY INC ( | | | SCAC4 |
| 16 | UPAO | UPDEGRAFF, MARK E | | | SCAC4 |
| 17 | UPAT | UPAT | | | SCAC4 |
| 18 | UPAU | CMC MATERIALS UPC LTD | | GB | BIC |
| 19 | UPAX | Utah Poultry Producers Cooperative Association Refrigerator Line | 7/1932 | | NAKINA |
| 20 | UPAX | Utah Poultry Producers Cooperative Association Refrigerator Line (North American Car Corp.) | 7/1935 | | NAKINA |
| 21 | UPAX | United Power Association | added 4/1982; 1/1994; eliminated 4/2000 | | NAKINA |
| 22 | UPAX | Great River Energy | added 4/2000; 7/2000-7/2005; eliminated 10/2005 | | NAKINA |
| 23 | UPAX | United Power Association | added 4/82; 1/94; eliminated 4/2000 | | NRHS |
| 24 | UPAX | Great River Energy | added 4/2000; 7/2000 | | NRHS |
| 25 | UPAX | *UTAH POULTRY PRODUCERS COOPERATIVE ASSOCIATION REFRIGERATOR LINE | | | PWRC |
| 26 | UPAX | *GREAT RIVER ENERGY [UNITED POWER ASSOCIATION] | | | PWRC |
| 27 | UPAX | United Power Association | | | RSRV |
| 28 | UPB | Air Foyle Charters Ltd. | Callsign: Kris, | GB | AVCODES |
| 29 | UPB | Union Pacific Railroad | | | RSRV |
| 30 | UPBZ | UNION PACIFIC RAILROAD COMPANY | | | PWRC |
| 31 | UPBZ | Union Pacific Railroad | | | RSRV |
| 32 | UPBZ | UNION PACIFIC RAILROAD | | | SCAC4 |
| 33 | UPC | Air Foyle Airways Ltd. | Callsign: Cutlass, | GB | AVCODES |
| 34 | UPCF | UNIQUE FREIGHT TRANSPORT INC | | | SCAC4 |
| 35 | UPCH | UPCHURCH, DEWEY TRUCKING | | | SCAC4 |
| 36 | UPCR | UNITED PETROLEUM CARRIERS | | | SCAC4 |
| 37 | UPCS | UNION PACIFIC CARRIER SERVICES | | | SCAC4 |
| 38 | UPCU | (UPCX) USPCI, INC. | | | PWRC |
| 39 | UPCU | USPCI Inc. | | | RSRV |
| 40 | UPCU | USPCCI | | | SCAC4 |
| 41 | UPCX | Universal Portland Cement Co. | 7/1923 | | NAKINA |
| 42 | UPCX | Universal Portland Cement Co. (Universal Atlas Cement Co.) | 7/1930-7/1935 | | NAKINA |
| 43 | UPCX | Universal Atlas Cement Co. | 7/1937-4/1938 | | NAKINA |
| 44 | UPCX | Union Petroleum Corp. | added 1/1962; 7/1965-4/1970; eliminated 4/1974 | | NAKINA |
| 45 | UPCX | Home Petroleum Corp. | added 4/1974; 1/1975; eliminated 10/1979; 1/1980 | | NAKINA |
| 46 | UPCX | USPCI c/o Laidlaw Environmental Services, Inc. | added 10/1995; eliminated 4/1996 | | NAKINA |
| 47 | UPCX | Laidlaw Environmental Services, Inc. | added 4/1996; 7/2000; eliminated 4/2002 | | NAKINA |
| 48 | UPCX | Clean Harbors Environmental Sciences, Inc. | 7/2005 (not listed) | | NAKINA |
| 49 | UPCX | Universal Portland Cement Co. (Universal Atlas Cement Co.) | Apr-38 | | NRHS |
| 50 | UPCX | Union Petroleum Corp. | added 1/62; 7/65-4/70 | | NRHS |
| 51 | UPCX | Home Petroleum Corp. | 1/75-1/80 | | NRHS |
| 52 | UPCX | USPCI c/o Laidlaw Environmental Services, Inc. | added 10/95; eliminated 4/96 | | NRHS |
| 53 | UPCX | Laidlaw Environmental Services, Inc. | added 4/96; 7/2000 | | NRHS |
| 54 | UPCX | *UNIVERSAL ATLAS CEMENT CO. [UNIVERSAL PORTLAND CEMENT CO.] | | | PWRC |
| 55 | UPCX | *HOME PETROLEUM CORP. [UNION PETROLEUM CORP.] | | | PWRC |
| 56 | UPCX | +CLEAN HARBORS ENVIRONMENTAL SCIENCES, INC [LAIDLAW ENVIRONMENTAL SERVICES INC.; USPCI, INC.] | | | PWRC |
| 57 | UPCX | Laidlaw Environmental Services | | | RSRV |
| 58 | UPCX | CLEAN HARBORS ENVIRONMENTAL SERVICE | | | SCAC4 |
| 59 | UPD | Air Foyle Charter Airlines Ltd. | IATA: G2, Callsign: Broadsword, Name changed to Air Foyle Passenger Airlines Limited | GB | AVCODES |
| 60 | UPD | Air Foyle Passenger Airlines Limited | IATA: G2, Callsign: Broadsword, Designator G2 recalled by IATA. Name changed from Air Foyle Charter Airlines Ltd. | GB | AVCODES |
| 61 | UPDC | UNION PACIFIC CARRIER SERVICES (DIV | | | SCAC4 |
| 62 | UPDL | U-PAK DISPOSALS (1989) LIMITED | | | SCAC4 |
| 63 | UPDM | UNION PACIFIC DE MEXICO | | | SCAC1 |
| 64 | UPDT | UPPER DECK TRANSPORT INC | | | SCAC4 |
| 65 | UPET | UNIFIED PETROLEUM | | | SCAC4 |
| 66 | UPFE | Union Pacific R.R. Co. | 1/1975-7/2005 | | NAKINA |
| 67 | UPFE | Union Pacific R.R. Co. | 1/75-7/2000 | | NRHS |
| 68 | UPFE | UNION PACIFIC RAILROAD COMPANY [PACIFIC FRUIT EXPRESS] | | | PWRC |
| 69 | UPFE | Pacific Fruit Express (Union Pacific Railroad) | | | RSRV |
| 70 | UPFS | UNION PACIFIC FREIGHT SERVICE | | | SCAC1 |
| 71 | UPFS | UNION PACIFIC DISTRIBUTION SERVICES | | | SCAC4 |
| 72 | UPFU | (UPUU) UNION PACIFIC BULKTAINER SERVICE | | | PWRC |
| 73 | UPFU | Union Pacific Bulktainer Service | | | RSRV |
| 74 | UPFU | UNION PACIFIC MOTOR FREIGHT CO. | | | SCAC4 |
| 75 | UPFX | United States Pipe and Foundry Co. | 7/1935-1/1943 | | NAKINA |
| 76 | UPFX | United States Pipe and Foundry Co. | Apr-38 | | NRHS |
| 77 | UPFX | UNITED STATES PIPE & FOUNDRY CO. | | | PWRC |
| 78 | UPGA | UPS FREIGHT (GROUND) | | | SCAC4 |
| 79 | UPGF | UPS FREIGHT | | | SCAC4 |
| 80 | UPGS | UNITED BEST TRANSPORT CORP | | | SCAC4 |
| 81 | UPGZ | UPS FREIGHT | | | SCAC4 |
| 82 | UPHY | UPLANDS PHEASANTRY | | | SCAC4 |
| 83 | UPHZ | Union Pacific Railroad | | | RSRV |
| 84 | UPHZ | UNION PACIFIC RAILROAD COMPANY | | | SCAC4 |
| 85 | UPIA | UNITED PRODUCTS INTERNATIONAL INC | | | SCAC4 |
| 86 | UPIX | USS-POSCO INDUSTRIES | | | PWRC |
| 87 | UPL | Ukrainian Pilot School | Callsign: Pilot School, | UA | AVCODES |
| 88 | UPL | Ukrainian Pilot School | | | ICAO1 |
| 89 | UPLD | UNITED PERISHABLE LOGISTICS LLC | | | SCAC4 |
| 90 | UPLG | U P LOGISTICS | | | SCAC4 |
| 91 | UPLH | UNION POWER LOGISTIC LLC | | | SCAC4 |
| 92 | UPLL | UPLAND LOGISTIC INC | | | SCAC4 |
| 93 | UPLT | UPLAND TRANSPORTATION INC | | | SCAC4 |
| 94 | UPLU | UPLINE CZ, S.R.O. | | CZ | BIC |
| 95 | UPM | Union Pacific R.R. Co. | 1/1980 | | NAKINA |
| 96 | UPM | Union Pacific R.R. Co. | Jan-80 | | NRHS |
| 97 | UPM | UNION PACIFIC RAILROAD, MILWAUKEE ROAD OPERATIONS | | | PWRC |
| 98 | UPM | Union Pacific Railroad | | | RSRV |
| 99 | UPMF | ULTRA-POLY MANUFACTURING INC | | | SCAC4 |
| 100 | UPMS | UNITED PETROLEUM SERVICES INC | | | SCAC4 |
