| 1301 | UNXN | UNIVERSAL EXPORTS INTERNATIONAL INC | | | SCAC4 |
| 1302 | UNXP | UNITED EXPRESS INC | | | SCAC4 |
| 1303 | UNXR | UNITED EXPRESS | | | SCAC4 |
| 1304 | UNXS | UNIFORM EXPRESS MOVERS LLC | | | SCAC4 |
| 1305 | UNXU | UNITAS CONTAINERS LIMITED | | BM | BIC |
| 1306 | UNXU | UNITAS CONTAINERS LIMITED | | | SCAC4 |
| 1307 | UNXX | CROWS NEST RESOURCES LTD | | | PWRC |
| 1308 | UNXX | CROWS NEST RESOURCES LTD | | | SCAC4 |
| 1309 | UNY | Lund University School of Aviation, TFHS | Callsign: University, | S | AVCODES |
| 1310 | UNY | Lund University School of Aviation | | | ICAO1 |
| 1311 | UNYC | UNITEC YORK INC | | | SCAC4 |
| 1312 | UNYT | UNYTREX INC | | | SCAC4 |
| 1313 | UO | Helicopters Hong Kong Limited | ICAO: HHK, Callsign: Helihongkong, Name changed to Hong Kong Express Airways Limited | HK | AVCODES |
| 1314 | UO | Trans-Union | | F | AVCODES |
| 1315 | UO | Empreas Aero Uruguay, S.A. | ICAO: AEU, Callsign: Uniform Oscar, | ROU | AVCODES |
| 1316 | UO | Helicopters Hong Kong Limited | ICAO: HHK, Callsign: Helihongkong, IATA designator changed to UO. Name changed from Helicopters Hong Kong Limited | HK | AVCODES |
| 1317 | UO | Hong Kong Express Airways Ltd | ICAO: HKE, Callsign: Hongkong Shuttle, | HK | AVCODES |
| 1318 | UO | Union R.R. of Oregon | 1/1975; added 7/1979; 1/1980; eliminated 4/1986; eliminated 4/1989 | | NAKINA |
| 1319 | UO | Union R.R. of Oregon | 1/75; added 7/79; 1/80; eliminated 4/86; eliminated 4/89 | | NRHS |
| 1320 | UO | RETIRED 08-23-93 ATP (000) [UNION RAILROAD OF OREGON] | | | PWRC |
| 1321 | UO | Union Railroad of Oregon | | | RSRV |
| 1322 | UO | UNION RAILROAD OF OREGON | | | SCAC4 |
| 1323 | UO | Union Railroad of Oregon | | USA | TRAFFIC |
| 1324 | UOAA | UNIVERSITY OF ALBERTA | | | SCAC4 |
| 1325 | UOAF | UNION OIL AND FARMERS UNION | | | SCAC4 |
| 1326 | UOBC | UNIVERSITY OF BRITISH COLUMBIA, THE | | | SCAC4 |
| 1327 | UOBT | UNITED SEA CARGO LLC | | | SCAC4 |
| 1328 | UOCR | UNITED OIL OF THE CAROLINAS INC | | | SCAC4 |
| 1329 | UOCS | UNIVERSITY OF CALIFORNIA SAN DIEGO | | | SCAC4 |
| 1330 | UOCX | Union Oil Co. of California | 8/1920-1/1952 | | NAKINA |
| 1331 | UOCX | General American Transportation Corp. | 7/1954-7/1965 | | NAKINA |
| 1332 | UOCX | Union Oil Co. of California (General American Transportation Corp.) | 10/1966 | | NAKINA |
| 1333 | UOCX | General American Transportation Corp. | 4/1970-1/1994; eliminated 1/1998 | | NAKINA |
| 1334 | UOCX | General American Marks Co. | added 1/1998; 7/2000-7/2005 | | NAKINA |
| 1335 | UOCX | Union Oil Co. of California | 4/38-1/52 | | NRHS |
| 1336 | UOCX | General American Transportation Corp. | 10/57-7/65 | | NRHS |
| 1337 | UOCX | Union Oil Co. of California (General American Transportation Corp.) | Oct-66 | | NRHS |
| 1338 | UOCX | General American Transportation Corp. | 4/70-1/94; eliminated 1/98 | | NRHS |
| 1339 | UOCX | General American Marks Co. | added 1/98; 7/2000 | | NRHS |
| 1340 | UOCX | GENERAL AMERICAN MARKS CO. [(GATC) GENERAL AMERICAN TRANSPORTATION CORP] UNION OIL CO. of CALIF.) | | | PWRC |
| 1341 | UOCX | Union Oil Co. of California (GATX) | | | RSRV |
| 1342 | UOEX | Union Oil Co. of California | added 10/1984; eliminated 1/1987 | | NAKINA |
| 1343 | UOEX | UNOCAL | added 1/1987; eliminated 7/1992 | | NAKINA |
| 1344 | UOEX | UNO-VEN | added 7/1992; 1/1994; eliminated 4/1998; 7/2000-7/2005 (not listed) | | NAKINA |
| 1345 | UOEX | Union Oil Co. of California | added 10/84; eliminated 1/87 | | NRHS |
| 1346 | UOEX | UNOCAL | added 1/87; eliminated 7/92 | | NRHS |
| 1347 | UOEX | UNO-VEN | added 7/92; 1/94; eliminated 4/98; 7/2000 | | NRHS |
| 1348 | UOEX | UNO-VEN [UNOCAL; UNION OIL CO. OF CALIFORNIA] | | | PWRC |
| 1349 | UOEX | UNO-VEN | | | RSRV |
| 1350 | UOEX | UNO-VEN | | | SCAC4 |
| 1351 | UOGA | UNITED OIL GRE | | | SCAC4 |
| 1352 | UOGX | United Oil & Natural Gas Products Corp. | 7/1923 | | NAKINA |
| 1353 | UOGX | UNITED OIL & NATURAL GAS PRODUCTS CORP. | | | PWRC |
| 1354 | UOGZ | UNIVERSITY OF GEORGIA | | | PWRC |
| 1355 | UOIC | UNNERSTALL OIL COMPANY | | | SCAC4 |
| 1356 | UOIG | URBAN ORGANICS INC | | | SCAC4 |
| 1357 | UOIK | UNITED OILFIELD INC | | | SCAC4 |
| 1358 | UOIN | UNIT ONE INC | | | SCAC4 |
| 1359 | UOKX | Union Oil Co. of Canada, Ltd. (Union Oil Co. of California) | 7/1930-7/1935 | | NAKINA |
| 1360 | UOKX | Union Oil Co. of Canada, Ltd. | 7/1937-1/1945 | | NAKINA |
| 1361 | UOKX | British American Oil Co. Ltd. | 1/1946-4/1947 | | NAKINA |
| 1362 | UOKX | Union Oil Co. of Canada Ltd. (Union Oil Co. of California) | Apr-38 | | NRHS |
| 1363 | UOKX | BRITISH AMERICAN OIL CO. [UNION OIL CO.] | | | PWRC |
| 1364 | UOLC | UNITED OIL CO | | | SCAC4 |
| 1365 | UOLT | UNITED OIL TRANSPORTATION | | | SCAC4 |
| 1366 | UOMN | UNISHIPPERS OF MICHIGAN | | | SCAC4 |
| 1367 | UONA | ULTIMATE ONE (1) | | | SCAC4 |
| 1368 | UONE | USA1 LOGISTICS INC | | | SCAC4 |
| 1369 | UOPX | Union Oil Co. of Pennsylvania | 7/1923 | | NAKINA |
| 1370 | UOPX | Union Oil Co. of Pennsylvania, Inc. | 7/1937 (not listed) | | NAKINA |
| 1371 | UOPX | UOP, A New York Partnership | added 1/1997; eliminated 7/1997; 7/2000-7/2005 (not listed) | | NAKINA |
| 1372 | UOPX | UOP, A New York Partnership | added 1/97; eliminated 7/97; 7/2000 | | NRHS |
| 1373 | UOPX | UOP A NEW YORK PARTNERSHIP [UNION OIL CO.] | | | PWRC |
| 1374 | UOPX | UOP New York | | | RSRV |
| 1375 | UOPX | UOP A NEW YORK PARTNERSHIP | | | SCAC4 |
| 1376 | UOSM | UNITED OCEAN SHIP MANAGEMENT PTE LT | | | SCAC4 |
| 1377 | UOT | UNICOM OIL TERMINAL SA | | RO | VKM |
| 1378 | UOTC | UNITED OVERSIZED TRUCKING INC | | | SCAC4 |
| 1379 | UOTI | UNID OCEAN TRANSPORT INC | | | SCAC4 |
| 1380 | UOTP | UPLAND ONE (1) TRANSPORTATION | | | SCAC4 |
| 1381 | UOUI | UNION OIL OF UNION IL INC | | | SCAC4 |
| 1382 | UP | Bahamasair | ICAO: BHS, Callsign: Bahamas, IATA Prefix: 111, Designator UP recall by IATA | BS | AVCODES |
| 1383 | UP | Bahamasair | ICAO: BHS, Callsign: Bahamas, IATA Prefix: 111, Name changed to Bahamasair Holdings Limited. Designator UP reinstated by IATA | BS | AVCODES |
| 1384 | UP | Air Foyle Limited | ICAO: UPA, Callsign: Foyle, IATA designator changed to GS | GB | AVCODES |
| 1385 | UP | Bahamasair Holdings Limited | ICAO: BHS, Callsign: Bahamas, IATA Prefix: 111, Name changed from Bahamasair. Designator UP reinstated by IATA | BS | AVCODES |
| 1386 | UP | Union Pacific R.R. Co. | 4/1961-7/2005 | | NAKINA |
| 1387 | UP | Union Pacific R.R. Co. | 4/61-7/2000 | | NRHS |
| 1388 | UP | UNION PACIFIC RAILROAD COMPANY | | | PWRC |
| 1389 | UP | Union Pacific Railroad | | | RSRV |
| 1390 | UP | UNION PACIFIC RAILROAD COMPANY | | | SCAC4 |
| 1391 | UP | Union Pacific | | USA | TRAFFIC |
| 1392 | UPA | Air Foyle Limited | IATA: GS, Callsign: Foyle, Designator recalled by IATA | GB | AVCODES |
| 1393 | UPA | Air Foyle Limited | IATA: UP, Callsign: Foyle, IATA designator changed to GS | GB | AVCODES |
| 1394 | UPA | Air Foyle Limited | Callsign: Foyle, Ceased operations. Designator recalled by IATA | GB | AVCODES |
| 1395 | UPA | Air Foyle | IATA: GS | | ICAO1 |
| 1396 | UPAC | UNITED PARCEL SERVICE COMPANY INC ( | | | SCAC4 |
| 1397 | UPAO | UPDEGRAFF, MARK E | | | SCAC4 |
| 1398 | UPAT | UPAT | | | SCAC4 |
| 1399 | UPAU | CMC MATERIALS UPC LTD | | GB | BIC |
| 1400 | UPAX | Utah Poultry Producers Cooperative Association Refrigerator Line | 7/1932 | | NAKINA |
