| 1 | MEC | Mercury Air Cargo, Inc. | IATA: BX, Callsign: Mercair, IATA designator changed to 4X | USA | AVCODES |
| 2 | MEC | Mercury Air Cargo, Inc. d/b/a Air Mercury | IATA: 4X, Callsign: Mercair, IATA Prefix: 805, IATA designator changed from BX* | USA | AVCODES |
| 3 | MEC | Mercury Aircourier Service | | | ICAO1 |
| 4 | MEC | Maine Central R.R. Co. | 7/1930-1/1994; eliminated 4/1997; added 7/1998; 7/2000-7/2005; eliminated 10/2006; added 4/2009 | | NAKINA |
| 5 | MEC | Maine Central R.R. Co. | 4/38-1/94; eliminated 4/97; added 7/98; 7/2000 | | NRHS |
| 6 | MEC | *ST RAIL SYSTEM | | | PWRC |
| 7 | MEC | +GUILFORD RAIL SYSTEM [MAINE CENTRAL RAILROAD] | | | PWRC |
| 8 | MEC | Maine Central Railroad (Pan Am Railways) | | | RSRV |
| 9 | MEC | Maine Central Railroad | | USA | TRAFFIC |
| 10 | MECA | MECCA & SON TRUCKING CORPORATION | | | SCAC1 |
| 11 | MECA | MECCA & SON TRUCKING CORP | | | SCAC4 |
| 12 | MECB | MAPLE CREEK BELGIANS | | | SCAC4 |
| 13 | MECC | Angelo Meccoli | | F | TRAFFIC |
| 14 | MECD | MISCO OF TERRE HAUTE INC | | | SCAC4 |
| 15 | MECDV | MECANO SERV SRL | | RO | VKM |
| 16 | MECG | MTT OF LACROSSE INC | | | SCAC4 |
| 17 | MECHA | MONTAJES ELÉCTRICOS CHAMORRO, S.A. | | ES | VKM |
| 18 | MECI | MARINE EXPLORATION CO INC | | | PWRC |
| 19 | MECJ | MIRANCY EXPRESS INC | | | SCAC4 |
| 20 | MECL | Museums Eisenbahn Club Losheim e.V. | Losheim | D | privat-bahn.de |
| 21 | MECL | MERCANA ART DECOR | | | SCAC4 |
| 22 | MECP | M E C EXPRESS LIMITED | | | SCAC4 |
| 23 | MECQ | MADSEN, SUSAN M | | | SCAC4 |
| 24 | MECS | Mecseki kisvasút - Pécs | | H | TRAFFIC |
| 25 | MECT | MORTENSON CONSTRUCTION | | | SCAC4 |
| 26 | MECU | MELFI MARINE CORP MAIN OFFICE | | | SCAC4 |
| 27 | MECX | Trinity Rail Management, Inc. | added 7/1997; 7/2000-7/2005; eliminated 1/2007 | | NAKINA |
| 28 | MECX | Transcisco Leasing Co. | added 7/1994; eliminated 7/1997 | | NAKINA |
| 29 | MECX | Miner-Edgar Chemical Corp. | 7/1930-7/1932 | | NAKINA |
| 30 | MECX | Miner-Edgar Co. | 8/1920-7/1923 | | NAKINA |
| 31 | MECX | Transcisco Leasing Co. | added 7/94; eliminated 7/97 | | NRHS |
| 32 | MECX | Trinity Rail Management, Inc. | added 7/97; 7/2000 | | NRHS |
| 33 | MECX | *MINER-EDGAR CHEMICAL CORP. | | | PWRC |
| 34 | MECX | *TRINITY RAIL MANAGEMENT INCORPORATED [TRANSCISCO LEASING COMPANY } | | | PWRC |
| 35 | MECX | Trinity Rail Management (Murray Energy Corp) | | | RSRV |
| 36 | MECY | MERCURY TRANSPORTATION INC | | | SCAC4 |
| 37 | MECZ | MILESTONE EQUIPMENT CORPORATION | | | SCAC4 |
