| 1 | ONT | Air Ontario | IATA: GX, Callsign: Ontario, Founded in June 1987. Merged into Air Canada Jazz in January 2001. Air Canada Connector | CDN | AVCODES |
| 2 | ONT | Government of Ontario | Callsign: Ontario Government, | CDN | AVCODES |
| 3 | ONT | Air Ontario | | | ICAO1 |
| 4 | ONT | Ontario Northland Ry. | 4/1947-7/2005 | | NAKINA |
| 5 | ONT | Ontario Northland Ry. | 1/52-7/2000 | | NRHS |
| 6 | ONT | ONTARIO NORTHLAND RAILWAY | | | PWRC |
| 7 | ONT | Ontario Northland Railway | | | RSRV |
| 8 | ONT | Ontario Northland Railway | | CDN | TRAFFIC |
| 9 | ONTA | Ontario Northland Ry. | added 1/1981; 1/1994-7/2005; eliminated 4/2006 | | NAKINA |
| 10 | ONTA | Ontario Northland Ry. | added 1/81; 1/94-7/2000 | | NRHS |
| 11 | ONTA | ONTARIO NORTHLAND RAILWAY | | | PWRC |
| 12 | ONTA | Ontario Northland Railway | | | RSRV |
| 13 | ONTB | OCEAN NAVIGATION THREE (3) CO LTD | | | SCAC4 |
| 14 | ONTC | O'NEILL TRANSFER COMPANY, INC | | | SCAC3 |
| 15 | ONTD | ON TIME DELIVERY SERVICE INC | | | SCAC3 |
| 16 | ONTE | ON TIME FREIGHT SYSTEM INC | | | SCAC3 |
| 17 | ONTG | OWEN, NORMAN TRUCKING | | | SCAC3 |
| 18 | ONTH | ONTIME TRANSPORT (1997) INC | | | SCAC4 |
| 19 | ONTI | ONAMOR TRUCKING INC | | | SCAC3 |
| 20 | ONTJ | ONTARIO-CAROLINAS TRANSFER | | | SCAC4 |
| 21 | ONTL | ON-TIME LIMOUSINE SERVICE LTD | | | SCAC3 |
| 22 | ONTM | ONE TWO THREE MESSENGER SERVICE INC | | | SCAC3 |
| 23 | ONTN | ONE TRANSPORTATION SERVICE, INC | | | SCAC3 |
| 24 | ONTN | ONE TRANSPORTATION SERRVICE INC | | | SCAC4 |
| 25 | ONTO | ONEILL TRANSPORT SERVICE | | | SCAC3 |
| 26 | ONTP | OCEAN AIR TRANSPORT INC | | | SCAC4 |
| 27 | ONTQ | ONTARIO TRUCKING CORP | | | SCAC3 |
| 28 | ONTR | ONEILL TRANSFER INC | | | SCAC3 |
| 29 | ONTR | ONEILL TRANSFER INC | | | SCAC4 |
| 30 | ONTS | ONE THREE SEVEN LARK STREET CORP (1 | | | SCAC3 |
| 31 | ONTT | ON TIME TRUCKLINES INC | | | SCAC3 |
| 32 | ONTU | NEW ONTO SHIPPING INTERNATIONAL | | | SCAC4 |
| 33 | ONTV | ON TIME MESSENGER SERVICE, INC | | | SCAC3 |
| 34 | ONTW | OCEAN NAVIGATION 2 CO LTD | | | SCAC4 |
| 35 | ONTX | On-Track Railcar Services, Inc. | added 4/1988; 1/1994-7/2005 | | NAKINA |
| 36 | ONTX | On-Track Railcar Services, Inc. | added 4/88; 1/94-7/2000 | | NRHS |
| 37 | ONTX | ON-TRACK RAILCAR SERVICES, INC. | | | PWRC |
| 38 | ONTX | On-Track Railcar Services | | | RSRV |
| 39 | ONTX | ON-TRACK RAILCAR SERVICES, INC. | | | SCAC4 |