| 2701 | OPIX | OXY USA Inc. | added 1/1991 | | NAKINA |
| 2702 | OPIX | OXY NGL, Inc. | eliminated 1/1991 | | NAKINA |
| 2703 | OPIX | OXY Petrochemicals Inc. | added 7/1990 | | NAKINA |
| 2704 | OPIX | OXY Petrochemicals Inc. | added 7/90 | | NRHS |
| 2705 | OPIX | OXY NGL, Inc. | eliminated 1/91 | | NRHS |
| 2706 | OPIX | OXY USA Inc. | added 1/91 | | NRHS |
| 2707 | OPIX | OXY Petrochemicals Inc. | eliminated 4/91 | | NRHS |
| 2708 | OPIX | Occidental Chemical Corp., Petrochemicals Division | added 4/91; eliminated 1/92 | | NRHS |
| 2709 | OPIX | Occidental Chemical Corp. | added 1/92; 1/94; eliminated 10/98 | | NRHS |
| 2710 | OPIX | Equistar Chemicals, LP | added 10/98; 7/2000 | | NRHS |
| 2711 | OPIX | EQUISTAR CHEMICALS, LP [OCCIDENTAL CHEMICAL CORP., - PETROCHEMICALS DIVISION; OXY USA, INC.; OXY NGL, INC.; OXY PETROCHEMICALS] | | | PWRC |
| 2712 | OPIX | Equistar Chemicals | | | RSRV |
| 2713 | OPJ | Opera Jet s.r.o. | Callsign: Opera Jet, | SK | AVCODES |
| 2714 | OPKM | OPTIKAM TECH INC | | | SCAC4 |
| 2715 | OPKS | PKS Opole | | PL | TRAFFIC |
| 2716 | OPKT | OVERPECK TRANSPORT CORP | | | SCAC4 |
| 2717 | OPKX | Onalaska Pickle & Canning Co. | 7/1935 | | NAKINA |
| 2718 | OPL | Air Cote D'opale, Sàrl | | F | AVCODES |
| 2719 | OPL | Air Cote D'opale, Sàrl | Callsign: Air Opale, | F | AVCODES |
| 2720 | OPLA | OCELOT PRIORITY LOGISTICS | | | SCAC4 |
| 2721 | OPLC | OPTIMUS LLC | | | SCAC4 |
| 2722 | OPLJ | OCEAN POINTS LOGISTICS LLC | | | SCAC4 |
| 2723 | OPLM | OPTIMA LIMOUSINE SERVICE INC | | | SCAC3 |
| 2724 | OPLM | ODYSSEY PERFORMANCE LIMITED | | | SCAC4 |
| 2725 | OPLN | ON POINT LOGISTICS INC | | | SCAC4 |
| 2726 | OPLQ | OAKLAND PORT LOGISTICS INC | | | SCAC4 |
| 2727 | OPLT | ORIENTAL POWER LOGISTICS CO LTD | | | SCAC4 |
| 2728 | OPLX | OREGON PACIFIC LINE, INC. | | | PWRC |
| 2729 | OPM | Fireblade Aviation (Pty) Ltd | Callsign: Optima, | ZA | AVCODES |
| 2730 | OPMC | OPTIMA LLC | | | SCAC4 |
| 2731 | OPMH | OPIES TRANSPORT INC | | | SCAC3 |
| 2732 | OPMH | OPIES TRANSPORT INC | | | SCAC4 |
| 2733 | OPN | Air Open Sky | Callsign: Air Sky, Ceased operations during November 2000. | F | AVCODES |
| 2734 | OPN | K&R Aviation, LLC | Callsign: Openair, | USA | AVCODES |
| 2735 | OPNF | OPEN FREIGHT INC | | | SCAC4 |
| 2736 | OPOC | OREGON POTATO COMPANY | | | SCAC4 |
| 2737 | OPOG | O & P OIL & GAS INC | | | SCAC4 |
| 2738 | OPOLE | Miejski Zakład Komunikacyjny, Opole | City: Opole | PL | TRAFFIC |
| 2739 | OPOR | ORTOPED INC | | | SCAC4 |
| 2740 | OPPE | OPPEL, F M | | | SCAC4 |
| 2741 | OPPI | OPPORTUNITY TRUCKING INC | | | SCAC3 |
| 2742 | OPPI | OPTECH INCORPORATED | | | SCAC4 |
| 2743 | OPPR | OPPERMAN, HARLAN | | | SCAC3 |
| 2744 | OPPR | OPAL RESOURCES CANADA INC | | | SCAC4 |
| 2745 | OPPS | ONSITE PETROLEUM PRODUCTS | | | SCAC4 |
| 2746 | OPPX | Omaha Public Power District | added 7/1994; 7/2000-7/2005 | | NAKINA |
| 2747 | OPPX | Oppenheimer Casing Co. | 7/1932 | | NAKINA |
| 2748 | OPPX | Oppenheimer Casing Co. (Union Refrigerator Transit Co.) | 7/1935 | | NAKINA |
| 2749 | OPPX | Omaha Public Power District | added 7/94; 7/2000 | | NRHS |
| 2750 | OPPX | *OPPENHEIMER CASING CO. | | | PWRC |
| 2751 | OPPX | +OMAHA PUBLIC POWER DISTRICT | | | PWRC |
| 2752 | OPPX | Omaha Public Power District | | | RSRV |
| 2753 | OPPX | OMAHA PUBLIC POWER DISTRICT | | | SCAC4 |
| 2754 | OPPZ | OSAGE POWER PLANT | | | PWRC |
| 2755 | OPR | Operaciones Aviacore, S.A. de C.V. | Callsign: Aviacore, | MEX | AVCODES |
| 2756 | OPR | Oregon Pacific R.R. Co. | 7/2000-7/2005 | | NAKINA |
| 2757 | OPR | Oregon Pacific R.R. Co. | Jul-00 | | NRHS |
| 2758 | OPR | OREGON PACIFIC RAILROAD | | | PWRC |
| 2759 | OPR | Oregon Pacific Railroad | | | RSRV |
| 2760 | OPR | OREGON PACIFIC RAILROAD CO | | | SCAC4 |
| 2761 | OPRC | OPERATIONAL COURIER SERVICE INC | | | SCAC3 |
| 2762 | OPRC | O P D I LOGISTICS CORP | | | SCAC4 |
| 2763 | OPRD | OPENROAD TRANSPORTATION INC | | | SCAC4 |
| 2764 | OPRE | OPEN ROAD EXPRESS INC | | | SCAC3 |
| 2765 | OPRU | OPERATOR LLC | | RUS | BIC |
| 2766 | OPRU | OPERATOR C LTD | | | SCAC4 |
| 2767 | OPS | Jet Ops | IATA: J6, Callsign: Ops-Jet, Designator J6* recalled by IATA | UAE | AVCODES |
| 2768 | OPS | Jet Ops | Callsign: Ops-Jet, Designator J6* recalled by IATA | UAE | AVCODES |
| 2769 | OPS | Jet-Ops | | | ICAO1 |
| 2770 | OPSA | OPERADORA DE TRANSPORTE INTERNACION | | | SCAC4 |
| 2771 | OPSB | OCEAN PRIDE SEAFOODS LTD | | | SCAC4 |
| 2772 | OPSC | OVERSEAS PUGET SOUND CHARTERER LLC | | | SCAC4 |
| 2773 | OPSE | OCEAN PACIFIC SEAFOOD | | | SCAC4 |
| 2774 | OPSI | OLYMPIC PAVING STONE INC | | | SCAC4 |
| 2775 | OPSL | OFFICIAL LIST OF OPEN AND PREPAY ST | | | SCAC3 |
| 2776 | OPSM | OPEN SEA MARITIME CORPORATION | | | SCAC3 |
| 2777 | OPSP | OCEAN PORT SERVICES CORP | | | SCAC4 |
| 2778 | OPSQ | OCEAN PRINCESS SHIPPING LIMITED | | | SCAC3 |
| 2779 | OPSQ | OCEANPRINCE INVESTMENTS LTD | | | SCAC4 |
| 2780 | OPSS | OCEAN PORT SERVICES LLC | | | SCAC4 |
| 2781 | OPSU | EMP | | | PWRC |
| 2782 | OPSX | Public Service Co. of Oklahoma | added 1/1979; 1/1980-7/2005 | | NAKINA |
| 2783 | OPSX | Public Service Co. of Oklahoma | added 1/79; 1/80-7/2000 | | NRHS |
| 2784 | OPSX | PUBLIC SERVICE COMPANY OF OKLAHOMA | | | PWRC |
| 2785 | OPSX | Public Service of Oklahoma | | | RSRV |
| 2786 | OPSX | PUBLIC SERVICE COMPANY OF OKLAHOMA | | | SCAC4 |
| 2787 | OPT | Corporate Wings, Inc. | Callsign: Options, Name changed to Flight Options | USA | AVCODES |
| 2788 | OPT | Flight Options | Callsign: Options, Name changed from Corporate Wings, Inc. | USA | AVCODES |
| 2789 | OPT | Edgley Aircraft Ltd. | Callsign: Optica, Name changed to Optica Industries | GB | AVCODES |
| 2790 | OPT | Optica Industries | Callsign: Optica, Name changed from Edgley Aircraft Ltd. | GB | AVCODES |
| 2791 | OPT | Flight Options | | | ICAO1 |
| 2792 | OPT | Orange Port Terminal Ry. | 7/2000-7/2005 | | NAKINA |
| 2793 | OPT | Orange Port Terminal Ry. | Jul-00 | | NRHS |
| 2794 | OPT | ORANGE PORT TERMINAL RAILWAY | | | PWRC |
| 2795 | OPT | Orange Port Terminal Railway | | | RSRV |
| 2796 | OPT | ORANGE PORT TERMINAL RAILWAY | | | SCAC4 |
| 2797 | OPTARE | Optare | | GB | TRAFFIC |
| 2798 | OPTC | OCEAN PORT TRANSPORT INC | | | SCAC4 |
| 2799 | OPTD | OPTIMODAL INC | | | SCAC4 |
| 2800 | OPTE | OPTEST EQUIPMENT INC | | | SCAC4 |
