| 1 | MER | Methow Aviation, Inc. | Callsign: Methow, | USA | AVCODES |
| 2 | MER | Methow Aviation | | | ICAO1 |
| 3 | MER | Macquarie European Rail Limited (Luxembourg Branch) | | LU | VKM |
| 4 | MERA | MERADA TRANSPORTATION LTD | | | SCAC4 |
| 5 | MERA | Metrans Rail | Real: MT | CZ | TRAFFIC |
| 6 | MERCER | Mercer Metro | | USA | TRAFFIC |
| 7 | MERCURY | Ford Mercury | | USA | TRAFFIC |
| 8 | MERE | MULTI EXTERIORS & RENOVATIONS USA I | | | SCAC4 |
| 9 | MERF | MERKS FARMS LTD | | | SCAC4 |
| 10 | MERK | MERRICK ENGINEERING INC | | | SCAC4 |
| 11 | MERN | MERIDIAN OPERATIONS LLC | | | SCAC4 |
| 12 | MERP | MERIT TRANSPORT LIMITED | | | SCAC4 |
| 13 | MERQ | MEDICAL EDUCATION & RESEARCH INSTIT | | | SCAC4 |
| 14 | MERR | Morristown & Erie Ry. Inc. d/b/a Maine Eastern R.R. | added 1/2004; eliminated 7/2004; 7/2005 | | NAKINA |
| 15 | MERR | MORRISTOWN & ERIE RWY. INC. d/b/a MAINE EASTERN RAILROAD | | | PWRC |
| 16 | MERR | Maine Eastern Railroad | | | RSRV |
| 17 | MERR | MAINE EASTERN RAILROAD | | | SCAC4 |
| 18 | MERR | Maine Eastern Railroad | | USA | TRAFFIC |
| 19 | MERS | MERCHA | | | SCAC4 |
| 20 | MERS | Arriva Trains Merseyside (former Merseyrail Electrics) | Real: ATM, 1999: 120km standard gauge, electrified at 750V= 3rd rail Merseyrail is the name given to the electric commuter train network centred on Liverpool. The name was used as the official brand for the network in the days of British Rail, and has stuck through several franchise holders. Merseyrail is one of the most frequent British commuter systems outside London, transporting 100,000 passengers a day, with services running (on average) every 15 minutes during weekday daytime, and 30 minutes at evenings and weekends. Services run on two lines covering the Liverpool suburban area and greater Merseyside, with a total track length of 120 km, and 67 stations. | GB | TRAFFIC |
| 21 | MERSB | Merseybus | 1986 - | GB | TRAFFIC |
| 22 | MERT | MERCHANT TRANSPORT | | | SCAC4 |
| 23 | MERU | MARIANA EXPRESS LINES PTE LTD | | SGP | BIC |
| 24 | MERU | MERZARIO LINE | | | SCAC1 |
| 25 | MERU | MERZARIO S.P.A.*ANDREA | | | SCAC4 |
| 26 | MERULA | UAB Merula | | LT | TRAFFIC |
| 27 | MERVAL | Metro Regional de Valparaíso S.A. | | RCH | TRAFFIC |
| 28 | MERW | Mercersburg Ry., Inc. | added 4/1979; 1/1980; added 7/1980; eliminated 1/1981 | | NAKINA |
| 29 | MERW | Mercersburg Ry., Inc. | added 4/79; 1/80; added 7/80; eliminated 1/81 | | NRHS |
| 30 | MERW | MERCERBURG RAILWAY INC. | | | PWRC |
| 31 | MERX | Merco, A Joint Venture | 1/1994 (not listed); added 1/1997; 7/2000; eliminated 7/2002 | | NAKINA |
| 32 | MERX | Merchants Despatch Transportation Co. | 4/1961-4/1970; eliminated 1/1973 | | NAKINA |
| 33 | MERX | Mercantile Refrigerator Line (Merchants Despatch Transportation Corp.) | 7/1937; 4/1938-10/1957 | | NAKINA |
| 34 | MERX | The Mecca Refining Co. | 7/1923 | | NAKINA |
| 35 | MERX | Mercantile Refrigerator Line (Merchants Despatch Transportation Corp.) | 1/52-10/57 | | NRHS |
| 36 | MERX | Merchants Despatch Transportation Co. | 4/61-4/70; eliminated 1/73 | | NRHS |
| 37 | MERX | Merco, A Joint Venture | 1/94; added 1/97; 7/2000 | | NRHS |
| 38 | MERX | *MECCA REFINING CO. | | | PWRC |
| 39 | MERX | *MERCANTILE REFRIGERATOR LINE (MERCHANTS DESPATCH TRANSPORTATION CORP.) | | | PWRC |
| 40 | MERX | *MERCO, A JOINT VENTURE | | | PWRC |
| 41 | MERX | Merco | | | RSRV |
| 42 | MERX | MERLIN PLASTICS SUPPLY INC | | | SCAC4 |
| 43 | MERZ | MERIDIAN | | | PWRC |
