| 1 | UM | Air Zimbabwe (PVT) Ltd. | ICAO: AZW, Callsign: Air Zimbabwe, IATA Prefix: 168, Name changed from Air Zimbabwe Corporation | ZW | AVCODES |
| 2 | UM | Air Zimbabwe Corporation | ICAO: AZW, Callsign: Air Zimbabwe, IATA Prefix: 168, Name changed to Air Zimbabwe (PVT) Ltd. | ZW | AVCODES |
| 3 | UM | Air Manila, Inc. | ICAO: AMI, Callsign: Airman, Founded in 1964. Merged into Philippine Airlines during 1973. | RP | AVCODES |
| 4 | UMA | Lineas Aereas Del Humaya, S.A. de C.V. | Callsign: Humaya, | MEX | AVCODES |
| 5 | UMA | Lineas Aereas del Humaya | | | ICAO1 |
| 6 | UMAI | U AND M TRUCKING | | | SCAC4 |
| 7 | UMAN | UMA TRANSPORTATION INC | | | SCAC4 |
| 8 | UMAU | UNITED MICROELECTRONICS CORPORATION (SINGAPORE BRANCH) | | SGP | BIC |
| 9 | UMB | Air Umbria, Societa | Callsign: Air Umbria, | I | AVCODES |
| 10 | UMB | Air Umbria | | | ICAO1 |
| 11 | UMBI | UMBRA INC | | | SCAC4 |
| 12 | UMCL | UMC LOGISTICS INC | | | SCAC4 |
| 13 | UMCN | UNIOCEAN MARITIME CO LTD | | | SCAC4 |
| 14 | UMCU | MERCHANT & CHAPMAN | | NL | BIC |
| 15 | UMCU | UZBEK MARITIME CORPORATION | | | SCAC4 |
| 16 | UMDW | UPPER MIDWEST SLEEP LLC | | | SCAC4 |
| 17 | UMEI | ULTIMATE MEDIA EXPRESS INC | | | SCAC4 |
| 18 | UMET | U-MING MARINE TRANSPORT (SINGAPORE) | | | SCAC4 |
| 19 | UMFF | UNITED MAYFLOWER CONTAINER SERVICES | | | SCAC4 |
| 20 | UMFI | UNITED MOTOR FREIGHT INC | | | SCAC4 |
| 21 | UMFO | ULLOA MONTANO, FRANCISCO | | | SCAC4 |
| 22 | UMFT | US MIDWEST FREIGHT INCORPORATED | | | SCAC4 |
| 23 | UMHL | UMMAH LLC | | | SCAC4 |
| 24 | UMIL | ULTIMATE INNOVATIONS LLC | | | SCAC4 |
| 25 | UMIN | UMINA BROS INC | | | SCAC4 |
| 26 | UMJU | AS CONTAINERHANDEL & SERVICE GMBH | | D | BIC |
| 27 | UMK | Aviation Transport Company Yuzmashavia | IATA: 2N, Callsign: Yuzmash, | UA | AVCODES |
| 28 | UMK | Yuzhmashavia | IATA: 2N | | ICAO1 |
| 29 | UMLD | UNICORN MOTORS LTD | | | SCAC4 |
| 30 | UMLS | USMEX LOGISTICS SERVICES LLC | | | SCAC4 |
| 31 | UMLT | UNIMARK LOWBOY TRANSPORTATION INC | | | SCAC4 |
| 32 | UMLU | SMART BULK TERMINAL LIMITED LIABILITY COMPANY | | RUS | BIC |
| 33 | UMMN | UNITED MARINE MANAGEMENT | | | SCAC4 |
| 34 | UMMT | U-MING MARINE TRANSPORT CORPORATION | | | SCAC4 |
| 35 | UMNL | UNITED MARINE NAVIGATION LIMITED, M | | | SCAC4 |
| 36 | UMOL | UHI MARCO OCEAN TRANSPORTATION LIMI | | | SCAC4 |
| 37 | UMOVE | Umove a/s | | DK | TRAFFIC |
| 38 | UMP | Upper Merion and Plymouth R.R. Co. | 7/1954-7/2005 | | NAKINA |
| 39 | UMP | Upper Merion and Plymouth R.R. Co. | 10/57-7/2000 | | NRHS |
| 40 | UMP | UPPER MERION & PLYMOUTH RAILROAD COMPANY | | | PWRC |
| 41 | UMP | Upper Merion and Plymouth Railroad | | | RSRV |
| 42 | UMP | Upper Merion and Plymouth R.R. Co. | | USA | TRAFFIC |
| 43 | UMPI | UNIVERSAL METAL PRODUCTS INC | | | SCAC4 |
| 44 | UMPX | Upper Merion & Plymouth Leasing Co. | added 4/1980; eliminated 4/1989 | | NAKINA |
| 45 | UMPX | Upper Merion and Plymouth Leasing Co. | added 4/1989; 1/1994 | | NAKINA |
| 46 | UMPX | Upper Merion and Plymouth Co. | eliminated 4/1996 | | NAKINA |
| 47 | UMPX | First Union Rail | added 4/1996; 7/2000-7/2005 | | NAKINA |
| 48 | UMPX | Upper Merion & Plymouth Leasing Co. | added 4/80; eliminated 4/89 | | NRHS |
| 49 | UMPX | Upper Merion and Plymouth Leasing Co. | added 4/89; 1/94 | | NRHS |
| 50 | UMPX | Upper Merion and Plymouth Co. | eliminated 4/96 | | NRHS |
| 51 | UMPX | First Union Rail | added 4/96; 7/2000 | | NRHS |
| 52 | UMPX | FIRST UNION RAIL [UPPER MERION & PLYMOUTH LEASING COMPANY] | | | PWRC |
| 53 | UMPX | Upper Merion and Plymouth Leasing | | | RSRV |
| 54 | UMPX | FIRST UNION RAIL | | | SCAC4 |
| 55 | UMRI | USA MEX REFRIGERATED TRANSPORT INC | | | SCAC4 |
| 56 | UMS | Unitemp-M, Limited Liability Industrial Company | Callsign: Topaz, | RUS | AVCODES |
| 57 | UMS | Unitemp-M | | | ICAO1 |
| 58 | UMSA | UGLAND MARINE SERVICES AS | | | SCAC4 |
| 59 | UMSC | UNIVERSITY MOVING & STORAGE COMPANY | | | SCAC4 |
| 60 | UMSD | UNIVERSITY MOVING & STORAGE COMPANY | | | SCAC4 |
| 61 | UMST | UMS TRUCKING | | | SCAC4 |
| 62 | UMSX | UNITED STEELWORKERS OF AMERICA | | | PWRC |
| 63 | UMSZ | INTERMODAL SERVICES, INC. | | | PWRC |
| 64 | UMSZ | Maersk Equipment Services | | | RSRV |
| 65 | UMSZ | MAERSK EQUIPMENT SERVICE COMPANY | | | SCAC4 |
| 66 | UMTC | ULTRA MARINE TRANSPORT CORP | | | SCAC4 |
| 67 | UMTI | U MOTORS INC | | | SCAC4 |
| 68 | UMTU | ULTRAMAR LLC | | RUS | BIC |
| 69 | UMVS | UNIVERSITY MOVING & STORAGE CO | | | SCAC4 |
| 70 | UMXF | UMEX FREIGHT SYSTEM INC | | | SCAC4 |
| 71 | UMXU | CSX TRANSPORTATION INC | | | SCAC4 |
