| 901 | OEFC | OVERTIME EXPRESS FREIGHT CO | | | SCAC3 |
| 902 | OEFC | OCEANLAND DISTRIBUTION SERVICES LTD | | | SCAC4 |
| 903 | OEFE | OMADA FURNITURE INC | | | SCAC4 |
| 904 | OEFI | ONE FIVE ONE ZERO NINE EIGHT EIGHT | | | SCAC4 |
| 905 | OEFT | ONE EIGHT FOUR THREE-SEVEN FOUR SEV | | | SCAC3 |
| 906 | OEG | Orient Eagle Airways | IATA: 4R, Callsign: Orienteagle, Ceased operations | KZ | AVCODES |
| 907 | OEG | Oberrheinische Eisenbahn-Gesellschaft AG | Mannheim | D | privat-bahn.de |
| 908 | OEG | Oberrheinische Eisenbahngesellschaft (Mannheim) | City: Mannheim | D | TRAFFIC |
| 909 | OEGI | OCTANE EXPRESS GROUP INC | | | SCAC4 |
| 910 | OEGIE | Stiftung BSW, Oberhessische Eisenbahnfreunde Gießen | | DE | VKM |
| 911 | OEGL | OPEL EYE GROUP LTD | | | SCAC4 |
| 912 | OEGU | OEG OFFSHORE GROUP LIMITED | | SGP | BIC |
| 913 | OEGU | OEG OFFSHORE PTE LTD | | | SCAC4 |
| 914 | OEHB | OEHLERT BROS INC | | | SCAC4 |
| 915 | OEHL | OEHLKE TRUCK LINE | | | SCAC3 |
| 916 | OEHM | OEHME CARRIER CORPORATION | | | SCAC4 |
| 917 | OEHQ | OEHRLEIN TRUCKING | | | SCAC3 |
| 918 | OEHR | OEHRLEIN SALT SALES | | | SCAC3 |
| 919 | OEIB | O E I BUSINESS FORMS | | | SCAC3 |
| 920 | OEIB | OEHLERKING HAULING | | | SCAC4 |
| 921 | OEIC | OWENS EXPRESS INC | | | SCAC3 |
| 922 | OEID | ONDAR EXPRESS INC | | | SCAC4 |
| 923 | OEIK | ONYX ENTERPRISES INC | | | SCAC4 |
| 924 | OEIN | OCEAN EXPRESS INC | | | SCAC4 |
| 925 | OEIP | ONTIME EXPRESS INC | | | SCAC4 |
| 926 | OEL | Ontario Express Ltd. | IATA: 9X, Callsign: Partner, Canadian Partner | CDN | AVCODES |
| 927 | OELD | OAHU EXPRESS LTD | | | SCAC4 |
| 928 | OELE | ORLANDO ENTERPRISE LLC | | | SCAC4 |
| 929 | OELL | OTTOMAN ENTERPRISES LLC | | | SCAC4 |
| 930 | OELN | ONTIME EXPRESS LINE INC | | | SCAC4 |
| 931 | OELX | O.E. Linsin, Inc. | 7/1935-4/1970; eliminated 4/1974 | | NAKINA |
| 932 | OELX | O.E. Linsin, Inc. | 4/38-4/70; eliminated 4/74 | | NRHS |
| 933 | OELX | O.E. LINSIN, INC. | | | PWRC |
| 934 | OELX | LINSIN INC, OE | | | SCAC3 |
| 935 | OENI | OSAGE ENTERPRISES INC | | | SCAC3 |
| 936 | OENI | OSAGE ENTERPRISES INC | | | SCAC4 |
| 937 | OENS | OWENS TRANSPORTATION LLC | | | SCAC4 |
| 938 | OEOE | OFFICE ENVIROMENTS OF N E | | | SCAC4 |
| 939 | OEOT | ONE EIGHT ONE EIGHT SIX THREE ZERO | | | SCAC4 |
| 940 | OEPF | OLD EL PASO (DIV OF | | | SCAC4 |
| 941 | OEPOST | Österreichische Bundespost: Postbus | | A | TRAFFIC |
| 942 | OEPT | OIL EXPRESS PETROLEUM TRANSPORT INC | | | SCAC3 |
| 943 | OEQN | OGILVY EQUESTRIAN | | | SCAC4 |
| 944 | OEQT | ORGANIC EQUIPMENT TECHNOLOGY | | | SCAC4 |
| 945 | OER | OREGON ELECTRIC RAILWAY | | | PWRC |
| 946 | OERR | OREGON EASTERN RAILROAD | | | PWRC |
| 947 | OERT | ORIENT EXPRESS CONTAINER CO LTD | | | SCAC4 |
| 948 | OERU | ORIENTAL EQUIPMENT SERVICES INC | | USA | BIC |
| 949 | OERX | SOUTHERN CALIFORNIA RAILWAY MUSEUM | | | SCAC4 |
| 950 | OERY | ORANGE EMPIRE RAILWAY MUSEUM | | | PWRC |
| 951 | OES | Omega-Express Service Ltd. | | RUS | AVCODES |
| 952 | OES | Art Aviation Flugbetriebs GmbH | Callsign: Art Austria, | A | AVCODES |
| 953 | OESC | ORIENT EXPRESS SERVICE COMPANY | | | SCAC3 |
| 954 | OESG | OLD ELM SPRING COLONY | | | SCAC4 |
| 955 | OESH | OCEAN EXCEL SHIPHOLDING SA | | | SCAC4 |
| 956 | OESI | OES INC | | | SCAC4 |
| 957 | OESO | OBESO TRANSPORT | | | SCAC4 |
| 958 | OESTE | | | E | TRAFFIC |
| 959 | OESV | OWEN EXPEDITED SERVICES | | | SCAC4 |
| 960 | OETE | OCEAN EXPRESS TRANSPORTATION AND EQ | | | SCAC4 |
| 961 | OETF | ONE EIGHT THREE SEVEN FIVE TWO FIVE | | | SCAC4 |
| 962 | OETG | OESTER TRUCKING | | | SCAC3 |
| 963 | OETG | OESTER TRUCKING INC | | | SCAC4 |
| 964 | OETI | OPTIMA EXPEDITED TRUCKING INC | | | SCAC4 |
| 965 | OETK | OETKEN BROS TRUCKING INC | | | SCAC3 |
| 966 | OETK | OETKEN BROS TRUCKING INC | | | SCAC4 |
| 967 | OETL | ODEN, TIM LLC | | | SCAC4 |
| 968 | OETN | ONE FOUR FIVE NINE EIGHT TWO NINE ( | | | SCAC4 |
| 969 | OETP | ONE-E TRANSPORT | | | SCAC4 |
| 970 | OETQ | OLIVER ERIE TRUCK SERVICE | | | SCAC3 |
| 971 | OETS | ORNELAS, ELIAS TRUCKING SERVICE | | | SCAC3 |
| 972 | OETT | OETTING & SONS | | | SCAC3 |
| 973 | OEW | One Airways, S.A.U. | IATA: OX, Callsign: Dreamer, | E | AVCODES |
| 974 | OEX | The Oak Extract Co. | 8/1920-7/1923 | | NAKINA |
| 975 | OEX | OAK EXTRACT CO. | | | PWRC |
| 976 | OEXC | OVERSIZE EXPRESS INC | | | SCAC4 |
| 977 | OEXE | ORCHID EXCHANGE | | | SCAC4 |
| 978 | OEXI | OUTERLIMITS EXCAVATION INC | | | SCAC4 |
| 979 | OEXT | OVERNITE EXPEDITE | | | SCAC4 |
| 980 | OEXU | MARGUISA SHIPPING LINES | | E | BIC |
| 981 | OEXU | ORNELL ENTREPRISES SA | | | SCAC4 |
| 982 | OEXX | ORFORD EXPRESS INC. | | | PWRC |
| 983 | OEXX | ORFORD EXPRESS INC | | | SCAC4 |
| 984 | OEY | PT Rimbun Abadi Aviasi d/b/a RIMBUN AIR | IATA: RI, Callsign: Rimbun Air, IATA Prefix: 273, | RI | AVCODES |
| 985 | OEYL | OAKLEY LOGISTICS INC | | | SCAC4 |
| 986 | OF | Transports et Travaux Aériens de Madagascar | ICAO: TML, Callsign: Tam Airline, | RM | AVCODES |
| 987 | OF | British Aircraft Corp. (BAC) (Filton Division) | | GB | AVCODES |
| 988 | OF | Air Finland Ltd. | ICAO: FIF, Callsign: Air Finland, Ceased operations and declared bankrupt on 26 June 2012. | FIN | AVCODES |
| 989 | OF | Overland Airways Limited | ICAO: OLA, Callsign: Overland, Commenced operations on 26 November 2003. IATA designator changed from OJ. | WAN | AVCODES |
| 990 | OFA | Helitaxi Ofavi, S.A. de C.V. | Callsign: Ofavi, | MEX | AVCODES |
| 991 | OFA | Helitaxi Ofavi | | | ICAO1 |
| 992 | OFAF | OUTBACK FUEL AND FEED LLC | | | SCAC4 |
| 993 | OFAH | OBERG FARMS | | | SCAC4 |
| 994 | OFAL | OFALLON GAS CO OF ST CHARLES COUNTY | | | SCAC3 |
| 995 | OFAM | OBERLE FARMS | | | SCAC4 |
| 996 | OFAS | OAHU FREIGHT ASSOCIATION | | | SCAC3 |
| 997 | OFBI | OMNI FREIGHT BROKERS INC | | | SCAC4 |
| 998 | OFBK | OSMAR FREIGHT BROKERS | | | SCAC4 |
| 999 | OFCC | OFC CORPORATION | | | SCAC4 |
| 1000 | OFCL | ONE FOUR SIX EIGHT ONE FOUR (146814 | | | SCAC3 |
