| 1501 | OISV | ONYX INDUSTRIAL SERVICES INC | | | SCAC4 |
| 1502 | OITF | OILFIELDS TRUCKING COMPANY | | | SCAC3 |
| 1503 | OITO | OVERSEAS INTERNATIONAL TOURS INC | | | SCAC3 |
| 1504 | OITS | OIL TRANSPORT SHIPPING LIMITED | | | SCAC3 |
| 1505 | OIUA | OILFIELD INSTRUMENTATION USA | | | SCAC4 |
| 1506 | OIX | Orion-X | Callsign: Orionx, | RUS | AVCODES |
| 1507 | OIX | Orion-x | | | ICAO1 |
| 1508 | OIXI | OIX INCORPORATED | | | SCAC4 |
| 1509 | OJ | Overland Airways Limited | ICAO: OLA, Callsign: Overland, Commenced operations on 26 November 2003. | WAN | AVCODES |
| 1510 | OJ | Maof Airlines | | IL | AVCODES |
| 1511 | OJ | Fly Jamaica Airways Limited | ICAO: FJM, Callsign: Greenheart, Founded in 2012, Commenced operations on 14 February 2013. Ceased operations on 31 March 2019. | JA | AVCODES |
| 1512 | OJ | Nyxair OU | ICAO: NYX, Callsign: Nyx Air, | EST | AVCODES |
| 1513 | OJA | Oriental Pearl Airways Ltd. | Callsign: Pearl, | GB | AVCODES |
| 1514 | OJAI | OJAI VAN LINES, INC | | | SCAC3 |
| 1515 | OJAM | OBERGFELL, JAMES | | | SCAC4 |
| 1516 | OJAS | ORTIZ, J A & SONS | | | SCAC4 |
| 1517 | OJAV | OTERO, JAVIER | | | SCAC4 |
| 1518 | OJCG | ORNELAS, JC TRUCKING | | | SCAC4 |
| 1519 | OJCK | O J C TRUCKING INC | | | SCAC3 |
| 1520 | OJCT | O. J. - COMMERCIAL TRANSPORT, INC | | | SCAC3 |
| 1521 | OJCT | OJC TRUCKING INC | | | SCAC4 |
| 1522 | OJES | O'CONNOR, JOHN E & SONS | | | SCAC3 |
| 1523 | OJET | OWENS, JAMES E TRUCKING INC | | | SCAC3 |
| 1524 | OJF | Occitania Jet Fleet | Callsign: Occitania, Ceased operations. | F | AVCODES |
| 1525 | OJF | Orsa Jernvägsförening | | SE | VKM |
| 1526 | OJFT | OCONNOR, JOHN F TRUCKING CO | | | SCAC3 |
| 1527 | OJGK | ODHAM, JOHN G TRUCKING | | | SCAC4 |
| 1528 | OJGR | OLDCASTLE/JOLLY GARDENER | | | SCAC4 |
| 1529 | OJGX | Oscar J. Glover | 1/1994-7/2005 (not listed) | | NAKINA |
| 1530 | OJGX | Oscar J. Glover | 1/94-7/2000 | | NRHS |
| 1531 | OJGX | OSCAR J. GLOVER | | | PWRC |
| 1532 | OJGX | Oscar J. Glover | | | RSRV |
| 1533 | OJGX | OSCAR J. GLOVER | | | SCAC4 |
| 1534 | OJIN | OJINAGA ROMU S DE R L DE C V (MX-33 | | | SCAC4 |
| 1535 | OJJ | Østjydske Jernbane | Real: ØJJ, 1876 - 1881 | DK | TRAFFIC |
| 1536 | OJLT | OLIVER, J L TRUCKING | | | SCAC4 |
| 1537 | OJML | OSORIO, JESUS MANUEL | | | SCAC4 |
| 1538 | OJO | OneJetOne Airways | Callsign: Ohjoh, Operations nevere started. | EAK | AVCODES |
| 1539 | OJON | O JOHNNY | | | SCAC4 |
| 1540 | OJS | Museiföreningen Örnsköldsviks JärnvägsSällskap | | SE | VKM |
| 1541 | OJT | Oryx Jet Ltd | Callsign: Orystar, | GB | AVCODES |
| 1542 | OJTG | O J TRUCKING INC | | | SCAC3 |
| 1543 | OJTI | OLE JAYS TRUCKING INC | | | SCAC3 |
| 1544 | OJTP | O-J TRANSPORT COMPANY | | | SCAC3 |
| 1545 | OJTX | Tauber Transportation Co. | added 7/1978; 1/1980; eliminated 7/1984; 1/1994 (not listed) | | NAKINA |
| 1546 | OJTX | O.J. Tauber | added 7/1957; 10/1957-7/1965; eliminated 10/1965 | | NAKINA |
| 1547 | OJTX | O.J. Tauber | 10/57-7/65; eliminated 10/65 | | NRHS |
| 1548 | OJTX | Tauber Transportation Co. | added 7/78; 1/80; eliminated 7/84; 1/94 | | NRHS |
| 1549 | OJTX | TAUBER TRANSPORTATION CO. [O. J. TAUBER] | | | PWRC |
| 1550 | OJTX | Tauber Transportation | | | RSRV |
| 1551 | OJVN | O J VENTURES LTD | | | SCAC4 |
| 1552 | OJY | Florida Air, Inc. | Callsign: Ohjay, | USA | AVCODES |
| 1553 | OJY | Florida Air | | | ICAO1 |
| 1554 | OK | Czech Airlines A.S. , CSA | ICAO: CSA, Callsign: CSA-Lines, IATA Prefix: 064, | CZ | AVCODES |
| 1555 | OK | Ceskoslovenske Aerolinie (CSA) | ICAO: CSA, Callsign: CSA-Lines, IATA Prefix: 064, | CS | AVCODES |
| 1556 | OK | Oklahoma Ry. Co. | 7/1923-1/1941 | | NAKINA |
| 1557 | OK | Oklahoma Ry. Co. | Apr-38 | | NRHS |
| 1558 | OK | OKLAHOMA RAILWAY CO. | | | PWRC |
| 1559 | OK | O&K | | B | TRAFFIC |
| 1560 | OKA | Okay Airways Company Limited | IATA: BK, Callsign: Okayjet, IATA Prefix: 866, Designator BK* reinstated by IATA | PRC | AVCODES |
| 1561 | OKA | Okay Airways | | | ICAO1 |
| 1562 | OKAM | OKAMI INC | | | SCAC4 |
| 1563 | OKAN | Okanagan Valley Ry. Co. | 7/2000-7/2005 | | NAKINA |
| 1564 | OKAN | Okanagan Valley Ry. Co. | Jul-00 | | NRHS |
| 1565 | OKAN | OKANAGAN VALLEY RAILWAY (OMNITRAX) | | | PWRC |
| 1566 | OKAN | Okanagan Valley Railway (OmniTRAX) | | | RSRV |
| 1567 | OKAN | OKANAGAN VALLEY RAILWAY COMPANY | | | SCAC4 |
| 1568 | OKAS | OKANOGAN-SEATTLE TRANSPORT COMPANY, | | | SCAC3 |
| 1569 | OKAT | OKA TRANSFER CO | | | SCAC3 |
| 1570 | OKAT | OKA TRANSFER CO, INC | | | SCAC4 |
| 1571 | OKAV | OAKLANE COLONY | | | SCAC4 |
| 1572 | OKAYAMA | Okayama Electric Tramway | City: Okayama | J | TRAFFIC |
| 1573 | OKB | Ostkustbanan | 1923 - 1933 | S | svenska-lok.se |
| 1574 | OKB | Sällskapet Ostkustbanans vänner | | SE | VKM |
| 1575 | OKBQ | OKEEFE, BINYON MOVING & STORAGE INC | | | SCAC3 |
| 1576 | OKBR | OAKLEY BARGE LINE INC | | | SCAC3 |
| 1577 | OKBR | OAKLEY BROTHERS TRUCKING | | | SCAC4 |
| 1578 | OKC | CZ Airlines, J.S.C. | | CZ | AVCODES |
| 1579 | OKC | Private Jets, Inc. | Callsign: Thunder Wings, | USA | AVCODES |
| 1580 | OKCC | OK'S CASCADE CO | | | SCAC3 |
| 1581 | OKCC | OMEGA TRUCKLINES INC | | | SCAC4 |
| 1582 | OKCE | Okarche Central Ry., Inc. | added 10/1982; eliminated 1/1983 | | NAKINA |
| 1583 | OKCE | Okarche Central Ry., Inc. | added 10/82; eliminated 1/83 | | NRHS |
| 1584 | OKCE | OKARCHE CENTRAL RAILWAY | | | PWRC |
| 1585 | OKCE | Okarche Central Railway | | | RSRV |
| 1586 | OKCG | OAK CARTAGE INC | | | SCAC3 |
| 1587 | OKCR | OKLAHOMA CITY RELOAD | | | SCAC4 |
| 1588 | OKCT | OKARCHE CENTRAL RAILWAY | | | PWRC |
| 1589 | OKCU | CAHAYA SAMUDERA SHIPPING PTE LTD | | | SCAC4 |
| 1590 | OKCX | Lone Star Industries, Inc. | added 7/1983; 1/1994-7/2000; eliminated 1/2001; added 7/2001; 7/2005 | | NAKINA |
| 1591 | OKCX | Louisiana Cement Co., Inc. | added 10/1981; eliminated 7/1983 | | NAKINA |
| 1592 | OKCX | OKC Corp. | added 4/1980; eliminated 10/1981 | | NAKINA |
| 1593 | OKCX | OKC Corp. | added 4/80; eliminated 10/81 | | NRHS |
| 1594 | OKCX | Louisiana Cement Co., Inc. | added 10/81 | | NRHS |
| 1595 | OKCX | Lone Star Industries, Inc. | 1/94-7/2000; eliminated 1/2001; added 7/2001 | | NRHS |
| 1596 | OKCX | LONE STAR INDUSTRIES, INC. [LOUISIANA CEMENT CO.; OKC CORP.] | | | PWRC |
| 1597 | OKCX | Lone Star Industries | | | RSRV |
| 1598 | OKCX | LONE STAR INDUSTRIES, INC. | | | SCAC4 |
| 1599 | OKD | | | CZ | TRAFFIC |
| 1600 | OKDB | OKAY DISTRIBUTORS | | | SCAC3 |
