| 301 | OBTU | JIANGSU O-BEST NEW MATERIALS CO LTD | | PRC | BIC |
| 302 | OBUG | ORIGINAL BUG SHIRT COMPANY, THE | | | SCAC4 |
| 303 | OBUN | OBER-UNITED TRAVEL AGENCY | | | SCAC3 |
| 304 | OBVS | OCONNOR BROS VAN & STORAGE CO INC | | | SCAC3 |
| 305 | OBWL | OBRIEN WAREHOUSING & LOGISTICS INC | | | SCAC4 |
| 306 | OBWM | OBRIEN, W M TRANSPORT | | | SCAC4 |
| 307 | OBXG | OBX LOGISTICS | | | SCAC4 |
| 308 | OBXI | ORBIT TRANSPORT INC | | | SCAC4 |
| 309 | OBXN | OBX INTERNATIONAL INC | | | SCAC4 |
| 310 | OBXT | O B X TRANSPORT | | | SCAC4 |
| 311 | OBYR | OBYRNE, JOSEPH | | | SCAC3 |
| 312 | OBYS | OBRYAN TRANSPORT INC | | | SCAC4 |
| 313 | OBYT | OBOYLE TRANSFER CO INC | | | SCAC3 |
| 314 | OBZE | OCEAN BREEZE TRANSIT CO | | | SCAC3 |
| 315 | OBZE | OLD BUZZARD EXPRESS LLC | | | SCAC4 |
| 316 | OC | Sunshine Aviation SA | ICAO: SHS, Callsign: Sunshine, Designator OC recalled by IATA | CH | AVCODES |
| 317 | OC | Aircraft Operating Co. (Aerial Surveys) Ltd. | Callsign: Airphotos, | ZA | AVCODES |
| 318 | OC | Air California | ICAO: ACL, Callsign: Aircal, Founded in 1967. Merged into American Airlines during 1987. | USA | AVCODES |
| 319 | OC | Oriental Air Bridge Co. Ltd. | ICAO: ORC, Callsign: Oriental Bridge, IATA designator changed from O3. ICAO Designator changed to NGK. | J | AVCODES |
| 320 | OC | OLIN CORPORATION | | | PWRC |
| 321 | OC | Oregon & California Railroad | | USA | TRAFFIC |
| 322 | OC | Société du chemin de fer Orbe-Chavornay SA | | CH | VKM |
| 323 | OCA | Aserca Airlines, C.A. | IATA: R7, Callsign: Arosca, Ceased operations on 22 May 2018 | YV | AVCODES |
| 324 | OCA | Aeroservicios Carabobo C.A. Aserca | IATA: R7, | YV | AVCODES |
| 325 | OCA | Aserca Airlines | IATA: R7 | | ICAO1 |
| 326 | OCAA | ORCA CANADIAN TRANSPORT LTD | | | SCAC4 |
| 327 | OCAB | OUTSIDE CARRIER | | | SCAC4 |
| 328 | OCAC | OK COAL AND CONCRETE | | | SCAC4 |
| 329 | OCAH | OTAY CARGO | | | SCAC4 |
| 330 | OCAI | OCEAN AIRE INC | | | SCAC4 |
| 331 | OCAL | OCAL TRANSPORT CO | | | SCAC3 |
| 332 | OCAL | ONE FOUR SIX EIGHT ONE FOUR (146814 | | | SCAC4 |
| 333 | OCAM | OTG CARGO | | | SCAC4 |
| 334 | OCAP | OUTLAW CUSTOMS AND PERFORMANCE LTD | | | SCAC4 |
| 335 | OCAQ | OCEANIC LTD INC | | | SCAC3 |
| 336 | OCAR | OCEANAIR INC | | | SCAC3 |
| 337 | OCAR | OCEANAIR INC | | | SCAC4 |
| 338 | OCAS | OCEAN A/S | | | SCAC3 |
| 339 | OCAS | O C T | | | SCAC4 |
| 340 | OCAU | OCEANBOX CONTAINERS LTD | | CY | BIC |
| 341 | OCAU | OCE ANDENO, B.V. | | | SCAC3 |
| 342 | OCAY | OCEANIA TANKER CORPORATION | | | SCAC4 |
| 343 | OCBC | O C BRUMSHIRE CO | | | SCAC3 |
| 344 | OCBC | O C BRUMSHIRE CO | | | SCAC4 |
| 345 | OCBI | OCEAN BARGE INC | | | SCAC3 |
| 346 | OCBI | OCEAN BEAUTY SEAFOODS INC | | | SCAC4 |
| 347 | OCBQ | OCEAN BEACH TRF & STG CO | | | SCAC3 |
| 348 | OCBS | OCEANBRIDGE SHIPPING LTD | | | SCAC3 |
| 349 | OCBS | OCEANBRIDGE SHIPPING LTD | | | SCAC4 |
| 350 | OCBU | OCEAN BLUE FINANCE GROUP LIMITED | | HK | BIC |
| 351 | OCC | Occidental Airlines | | LB | AVCODES |
| 352 | OCC | German Forces Operations Control | | D | AVCODES |
| 353 | OCCC | O C C INC | | | SCAC3 |
| 354 | OCCC | OCEAN CARGO CARRIERS CO LLC | | | SCAC4 |
| 355 | OCCD | OCCIDENTAL SERVICES CORP | | | SCAC3 |
| 356 | OCCE | OCONNERS EXPRESS | | | SCAC3 |
| 357 | OCCE | OCONNERS EXPRESS INC | | | SCAC4 |
| 358 | OCCF | OKLAHOMA CUSTOM COURIER LLC | | | SCAC4 |
| 359 | OCCH | OVERLAND COACH INC | | | SCAC3 |
| 360 | OCCH | ON TIME MESSENGER SERVICE INC | | | SCAC4 |
| 361 | OCCI | OCCIDENTAL CARRIERS S.A. | | | SCAC3 |
| 362 | OCCI | OCCIDENTAL E N E | | | SCAC4 |
| 363 | OCCL | ORANGE COUNTY CONTAINER GROUP LLC | | | SCAC4 |
| 364 | OCCP | OLYMPIC CARRIER CORPORATION | | | SCAC3 |
| 365 | OCCP | OCEAN STAR INTERNATIONAL LOGISTICS | | | SCAC4 |
| 366 | OCCQ | OCEANIA CRUISES INC | | | SCAC4 |
| 367 | OCCR | OCEANSTAR CORPORATION | | | SCAC3 |
| 368 | OCCR | OCEAN CERAMICS LTD | | | SCAC4 |
| 369 | OCCS | OCEANIC SHIPPING CORP MONTREAUX SW | | | SCAC4 |
| 370 | OCCT | OCCIDENTAL TRANSPORTATION CO LTD | | | SCAC3 |
| 371 | OCCU | ORANGE CONTAINER LINE B.V. | | NL | BIC |
| 372 | OCCU | ATS CONTAINER LEASING S.A. | | | PWRC |
| 373 | OCCU | ATS Container Leasing SA | | | RSRV |
| 374 | OCCU | ORBIS CONTAINER SERVICE CORP., A.G. | | | SCAC3 |
| 375 | OCCV | ON CUSTOMS COURIER SERVICE INC | | | SCAC4 |
| 376 | OCCX | Occidental Chemical Corp. | added 1/1992; 1/1994-7/2005 | | NAKINA |
| 377 | OCCX | Occidental Chemical Corp. Agricultural Products | added 4/1989; eliminated 1/1992 | | NAKINA |
| 378 | OCCX | Occidental Chemical Corp. Agricultural Products Group | added 7/1988; eliminated 4/1989 | | NAKINA |
| 379 | OCCX | Occidental Chemical Agricultural Products, Inc. | added 1/1983; eliminated 7/1988 | | NAKINA |
| 380 | OCCX | Occidental Chemical Co. | added 4/1981; eliminated 1/1983 | | NAKINA |
| 381 | OCCX | Occidental Chemical Co. | added 4/81; eliminated 1/83 | | NRHS |
| 382 | OCCX | Occidental Chemical Agricultural Products, Inc. | added 1/83; eliminated 7/88 | | NRHS |
| 383 | OCCX | Occidental Chemical Corp. Agricultural Products Group | added 7/88; eliminated 4/89 | | NRHS |
| 384 | OCCX | Occidental Chemical Corp. Agricultural Products | added 4/89; eliminated 1/92 | | NRHS |
| 385 | OCCX | Occidental Chemical Corp. | added 1/92; 1/94-7/2000 | | NRHS |
| 386 | OCCX | OCCIDENTAL CHEMICAL CORP., AGRICULTURAL PRODUCTS | | | PWRC |
| 387 | OCCX | Occidental Chemical | | | RSRV |
| 388 | OCCX | OCCIDENTAL CHEMICAL CORPORATION | | | SCAC4 |
| 389 | OCCZ | OCCIDENTAL CHEMICAL CORP. | | | PWRC |
| 390 | OCDA | ONE CALL DOES IT ALL | | | SCAC4 |
| 391 | OCDG | ODECO TRADING INC | | | SCAC4 |
| 392 | OCDI | OCEAN DUCHESS INC | | | SCAC3 |
| 393 | OCDI | OLIVER CUSTOM DELIVERY LIMITED | | | SCAC4 |
| 394 | OCDN | OCCIDENTAL TOURS | | | SCAC3 |
| 395 | OCDN | OCEAN DANCER FISHING LTD | | | SCAC4 |
| 396 | OCDT | OCEANICA COMPANIA DE TRANSPORTES SA | | | SCAC3 |
| 397 | OCE | Helicocean | Callsign: Heliocean, | NC | AVCODES |
| 398 | OCE | Heliocean | | | ICAO1 |
| 399 | OCE | Oregon, California & Eastern Ry. Co. | 1/1975; added 4/1977; 1/1980; eliminated 4/1992; 1/1994 | | NAKINA |
| 400 | OCE | Oregon, California & Eastern Ry. Co. | 1/75-1/80; eliminated 4/92; 1/94 | | NRHS |
