| 1 | MRT | Air Mauritanie | IATA: MR, Callsign: Mike Romeo, IATA Prefix: 174, Designator MR reinsated by IATA. Founded in September 1962. Ceased operations during 2007. | RIM | AVCODES |
| 2 | MRT | Air Mauritanie | IATA: MR | | ICAO1 |
| 3 | MRT | Manila Metro Rail Transit System | Real: MRTS, City: Manila | RP | TRAFFIC |
| 4 | MRTA | MORRIS TRANSFER INC | | | SCAC4 |
| 5 | MRTC | MOVE-RITE & TRANSPORT | | | SCAC4 |
| 6 | MRTD | MRC TRANSPORT LLC | | | SCAC4 |
| 7 | MRTE | MORALES, T S | | | SCAC4 |
| 8 | MRTF | MARTINEZ FLORES, HUGO JAVIER | | | SCAC4 |
| 9 | MRTG | M & R TRUCKING-PORTAGE INC | | | SCAC4 |
| 10 | MRTJ | M R TRANSPORT | | | SCAC4 |
| 11 | MRTJ | Mass Rapid Transit Jakarta | City: Jakarta | RI | TRAFFIC |
| 12 | MRTL | M R TRADERS (PVT) LTD | | | SCAC4 |
| 13 | MRTM | MARITIME-ONTARIO FREIGHT LINES LTD | | | SCAC4 |
| 14 | MRTN | MR TRANSPORTATION SERVICES LLC | | | SCAC4 |
| 15 | MRTO | MOSHER, ROBERT TRANSPORT INC | | | SCAC4 |
| 16 | MRTQ | MARA TRANSPORT INC | | | SCAC4 |
| 17 | MRTR | MORROW TRUCKING INC | | | SCAC4 |
| 18 | MRTS | MARTIN TRANSPORTATION COMPANY | | | SCAC4 |
| 19 | MRTU | PT MERATUS LINE | | RI | BIC |
| 20 | MRTU | PT MERATUS LINE | | | SCAC4 |
| 21 | MRTX | Cemex, Inc. | added 1/2007 | | NAKINA |
| 22 | MRTX | Marx Hide & Tallow Co., Inc. | 7/1935-7/1937 | | NAKINA |
| 23 | MRTX | *MARX HIDE & TALLOW CO., INC. | | | PWRC |
| 24 | MRTX | +CEMEX, INC. | | | PWRC |
| 25 | MRTX | CEMEX INC | | | SCAC4 |
| 26 | MRTZ | TRAC INTERMODAL | | | SCAC4 |
