| 1 | OL | OLT-Ostfriesische Lufttransport | ICAO: OLT, Callsign: Oltra, IATA Prefix: 704, Name changed to OLT Express Germany GmbH. | D | AVCODES |
| 2 | OL | Odyssey International | ICAO: ODY, Callsign: Odyssey, Founded in June 1988. Ceased operations during April 1990. | CDN | AVCODES |
| 3 | OL | OLT Express Germany GmbH | ICAO: OLT, Callsign: Oltra, IATA Prefix: 704, Ceased operations on 27 January 2013 at 12:00pm. Name changed from OLT-Ostfriesische Lufttransport. | D | AVCODES |
| 4 | OL | Polynesian Limited | ICAO: PAO, Callsign: Polynesian, IATA Prefix: 162, Name changed to Samoa Airways in 2017. | WS | AVCODES |
| 5 | OL | Samoa Airways | ICAO: PAO, Callsign: Polynesian, IATA Prefix: 162, Name changed from Polynesian Limited in 2017. | WS | AVCODES |
| 6 | OL&I | Ogden, Logan & Idaho Ry. Co. (Utah Idaho Central R.R. Co.) | 7/1930 | | NAKINA |
| 7 | OL&I | UTAH IDAHO CENTRAL RAILROAD CO. [OGDEN, LOGAN & IDAHO RWY. CO.] | | | PWRC |
| 8 | OLA | Overland Airways Limited | IATA: OJ, Callsign: Overland, Commenced operations on 26 November 2003. | WAN | AVCODES |
| 9 | OLA | Overland Airways Limited | IATA: OF, Callsign: Overland, Commenced operations on 26 November 2003. IATA designator changed from OJ. | WAN | AVCODES |
| 10 | OLA | Overland Airways | IATA: OJ | | ICAO1 |
| 11 | OLA | Ostseeland Verkehr GmbH | Schwerin (Connex-Gruppe > Veolia Verkehr) | D | privat-bahn.de |
| 12 | OLA | Ostseeland Verkehr GmbH | | DE | VKM |
| 13 | OLAE | OLSEN, ARDEN E | | | SCAC3 |
| 14 | OLAF | OLD SALT FISHING CO LTD | | | SCAC4 |
| 15 | OLAG | OLAUGHLIN, LEO INC | | | SCAC3 |
| 16 | OLAO | OLD ALLEN AUTO SALES | | | SCAC3 |
| 17 | OLAP | OKANOGAN LABEL AND PRINT | | | SCAC4 |
| 18 | OLAT | OLATHE TRUCKING LLC | | | SCAC4 |
| 19 | OLAU | OCCIDENTAL CHEMICAL CORPORATION | | | PWRC |
| 20 | OLAU | Occidental Chemical Corporation | | | RSRV |
| 21 | OLAU | OCCIDENTAL CHEMICAL CORPORATION | | | SCAC3 |
| 22 | OLB | Omaha, Lincoln and Beatrice Ry. Co. | added 10/1974; 1/1975-7/2005 | | NAKINA |
| 23 | OLB | Omaha, Lincoln and Beatrice Ry. Co. | added 10/74; 1/75-7/2000 | | NRHS |
| 24 | OLB | OMAHA, LINCOLN & BEATRICE RAILWAY COMPANY | | | PWRC |
| 25 | OLB | Omaha, Lincoln and Beatrice Railway | | | RSRV |
| 26 | OLBC | OLIVER BUS CO (DIV OF R & R TRUCKIN | | | SCAC3 |
| 27 | OLBC | OLIN, LARRY M | | | SCAC4 |
| 28 | OLBE | OLD BRIDGE EXPRESS | | | SCAC3 |
| 29 | OLBH | OLSEN BROTHERS INC | | | SCAC3 |
| 30 | OLBI | OCEAN LINE OF BERMUDA INC. | | | SCAC3 |
| 31 | OLBK | OLSON BROS TRUCKING | | | SCAC3 |
| 32 | OLBO | OLSEN, W TRANSFER | | | SCAC3 |
| 33 | OLBZ | OLD BEN #25 MINE | | | PWRC |
| 34 | OLC | Solar Cargo, C.A. | IATA: 4S, Callsign: Solarcargo, IATA Prefix: 644, | YV | AVCODES |
| 35 | OLC | Solar Cargo | | | ICAO1 |
| 36 | OLCC | OLYMPIC CASCADE CORPORATION | | | SCAC3 |
| 37 | OLCI | OLSON CARRIERS INC | | | SCAC3 |
| 38 | OLCI | OVERLAND CUSTOM COACH (2007) INC | | | SCAC4 |
| 39 | OLCL | OLETA COACH LINES INC | | | SCAC3 |
| 40 | OLCL | OLSEN, L C L INC | | | SCAC4 |
| 41 | OLCM | ON THE LEVEL CARPENTRY & MILLWORK | | | SCAC4 |
| 42 | OLCN | OIL CENTRAL INC | | | SCAC4 |
| 43 | OLCT | O-LAND CONTAINER TRANSPORT INC | | | SCAC3 |
| 44 | OLCU | OILCORE UAB | | LT | BIC |
| 45 | OLCY | ORTHMAN LOGISTICS COMPANY | | | SCAC4 |
| 46 | OLD | Beijing Orenda Tribe General Aviation Co., Ltd. | Callsign: Air Orenda, | PRC | AVCODES |
| 47 | OLDB | OLD BAY TRANSFER | | | SCAC3 |
| 48 | OLDB | OLD BLACKSMITH SHOP, THE | | | SCAC4 |
| 49 | OLDC | OLD COLONY FILM TRANSFER CORP | | | SCAC3 |
| 50 | OLDE | OLD DUTCH EXPRESS INC | | | SCAC3 |
| 51 | OLDE | OLDE TOWN EXPRESS | | | SCAC4 |
| 52 | OLDH | OLDHAM, JAY F AND SON, INC | | | SCAC3 |
| 53 | OLDH | OLDHAM, JAY F AND SON, INC | | | SCAC4 |
| 54 | OLDHCT | Oldham Corporation Passenger Transport | | GB | TRAFFIC |
| 55 | OLDI | OLD IRON | | | SCAC4 |
| 56 | OLDJ | OLDHAM, JACK OIL INC | | | SCAC4 |
| 57 | OLDK | O L D TRUCKING | | | SCAC3 |
| 58 | OLDK | OLDENKAMP TRUCKING | | | SCAC4 |
| 59 | OLDL | OLDLAND DISTRIBUTING | | | SCAC3 |
| 60 | OLDO | OLDOVER CORPORATION | | | SCAC3 |
| 61 | OLDOP | OLOMOUCKÁ DOPRAVNI s.r.o. | | CZ | VKM |
| 62 | OLDP | OLD SCHOOL EXPRESS | | | SCAC4 |
| 63 | OLDQ | OLD DOMINION STEVEDORING CO | | | SCAC3 |
| 64 | OLDR | OLD RELIABLE TRANSPORT INC | | | SCAC3 |
| 65 | OLDR | OLD RELIABLE TRANSPORT INC | | | SCAC4 |
| 66 | OLDS | OLD SOUTH FREIGHT SERVICE INC | | | SCAC3 |
| 67 | OLDS | OLIVER, L D SEED CO INC | | | SCAC4 |
| 68 | OLDT | OLD SOUTH TRANSPORTATION CO INC | | | SCAC3 |
| 69 | OLDW | OLD WEST HARDWARE | | | SCAC4 |
| 70 | OLDX | Old Line Holding Co., Inc. | added 1/1992; 1/1994-7/2000; eliminated 10/2004; 7/2005 (not listed) | | NAKINA |
| 71 | OLDX | Old Line Holding Co., Inc. | added 1/92; 1/94-7/2000 | | NRHS |
| 72 | OLDX | OLD LINE HOLDING COMPANY, INC | | | PWRC |
| 73 | OLDX | Old Line Holding | | | RSRV |
| 74 | OLE | Operadora de Lineas Ejecutivas S.A. de C.V. | Callsign: Operadora, | MEX | AVCODES |
| 75 | OLE | Operadora de Lineas Ejecutivas | | | ICAO1 |
| 76 | OLEA | OLEARY TRANSPORTATION CO, INC | | | SCAC3 |
| 77 | OLEA | OUTLAW EAGLE MANUFACTURING LTD | | | SCAC4 |
| 78 | OLEE | OLD LVIV EXPRESS | | | SCAC4 |
| 79 | OLEO | OLERON TANKER S A | | | SCAC3 |
| 80 | OLEP | OLYMPIC EXPRESS | | | SCAC3 |
| 81 | OLEP | OFF LOAD EXPRESS | | | SCAC4 |
| 82 | OLEQ | OVERLAND EQUINE EXPRESS | | | SCAC3 |
| 83 | OLER | OLE ROCKNE | | | SCAC3 |
| 84 | OLES | OLE SAN MIGUEL | | | SCAC4 |
| 85 | OLFC | OLOFSSON CORP | | | SCAC3 |
| 86 | OLFE | OLD FORT EXPRESS COMPANBY INC | | | SCAC3 |
| 87 | OLFR | OZ-LU FURNITURE & DECOR | | | SCAC4 |
| 88 | OLFU | OLVI FORWARDING LTD | | CY | BIC |
| 89 | OLFV | ONLINE FREIGHT SERVICES INC | | | SCAC4 |
| 90 | OLFW | OLYMPIC FREIGHTWAYS INC | | | SCAC3 |
| 91 | OLFZ | OLYMPIC FOUNDRY | | | PWRC |
| 92 | OLGI | OCEANICA LOGISTICS GROUP INC | | | SCAC4 |
| 93 | OLGL | ORCHARDS LOGISTICS LLC | | | SCAC4 |
| 94 | OLGT | OLINGER TRUCKING INC | | | SCAC3 |
| 95 | OLGV | OCEAN LONGEVITY COMPANY | | | SCAC3 |
| 96 | OLGV | OCEAN LONGEVITY CO LTD | | | SCAC4 |
| 97 | OLGX | INOS Oligomers | added 1/2008 | | NAKINA |
| 98 | OLGX | INEOS OLIGOMERS, DIV. INEOS USE LLC | | | PWRC |
| 99 | OLGX | INEOS OLIGOMERS A DIVISION OF | | | SCAC4 |
| 100 | OLHC | OLEAN HAULING CORP | | | SCAC3 |
