| M | Montour R.R. Co. | 4/38-10/66 |
| MA | Missouri and Arkansas Ry. | Jan-52 |
| MAA | Magma Arizona R.R. Co. | 1/75-1/80; eliminated 1/94; 7/2000 |
| MAAX | Maxx Leasing Co. | added 1/81; eliminated 10/88 |
| MA&C | Minneapolis, Anoka and Cuyuna Range R.R. Co. | Apr-38 |
| MACR | Minneapolis, Anoka and Cuyuna Range R.R. Co. | Jan-75 |
| MACO | McCormick, Ashland City & Nashville R.R. Inc. | added 10/88; eliminated 1/93 |
| MACX | Magor Car Corp. | 7/65-10/66; eliminated 10/67 |
| Magor Railcar Division, Fruehauf Corp. | added 7/68; 4/70 | |
| Fruehauf Corp. | 1/75-1/80 | |
| Mac Acquisitions, L.P. | added 10/96; 7/2000 | |
| MAEX | Maersk, Inc. | added 7/90; eliminated 4/93; 1/94 |
| MAGX | Magnimet, Monroe Scrap Division (interplant service) | 1/80-1/94 |
| MAHX | Miller & Hart, Inc. (General American Transportation Corp.) | Apr-38 |
| General American Transportation Corp. | 1/52-4/61 | |
| MALX | Mid-America Locomotive & Car Repair, Inc. | Jul-00 |
| MANX | Bannock Leasing, Inc. | added 1/66; eliminated 10/66 |
| Manchester Gas Co. | added 4/74; 1/75-1/80; eliminated 4/89 | |
| EnergyNorth Natural Gas, Inc. | added 4/89; eliminated 1/96 | |
| Gas Supply, Inc. | eliminated 10/99 | |
| EnergyNorth Natural Gas, Inc. | Jan-94 | |
| Williams Energy Ventures, Inc. | added 10/99; 7/2000 | |
| MAPX | Mapco Products Co. | added 10/80; eliminated 4/85 |
| Mapco Petroleum, Inc. | added 4/85 | |
| Mapco Gas Products, Inc. | eliminated 10/93 | |
| Mapco Petroleum, Inc. | added 10/93; 1/94; eliminated 10/99 | |
| Williams Energy Ventures, Inc. | added 10/99; 7/2000 | |
| MAR | Missouri and Arkansas Ry. Co. | Apr-38 |
| MART | American Refrigerator Transit Co. | 4/61-10/66; eliminated 10/69 |
| MARX | Mather Stock Car Co. | added 10/53; eliminated 7/55 |
| North American Car Corp. | added 7/55; 10/57-4/70; eliminated 7/73 | |
| MidAmerican Energy Co. | added 10/98; 7/2000 | |
| MASX | North American Car Corp. | added 4/68; 4/70-1/80 |
| General Electric Railcar Services Corp. | 1/94; eliminated 10/94 | |
| MATX | Mid-American Car & Equipment Co. | added 7/65; 7/65-1/75; eliminated 4/75 |
| Merchants Investment Co. | added 4/75; 1/80; eliminated 1/89 | |
| Railmark | added 1/89 | |
| MAW | Maumee & Western R.R. Corp. | added 7/98; 7/2000 |
| MAWX | The Mathieson Alkali Works (Inc.) | Apr-38 |
| Mathieson Chemical Corp. | Jan-52 | |
| Olin Mathieson Chemical Corp. | 10/57-10/66; eliminated 1/70 | |
| Olin Corp. | added 1/70; 4/70; eliminated 4/73 | |
| MAX | Michigan Alkali Co. | Apr-38 |
| MAXX | MidAmerican Energy Co. | added 4/96; 7/2000 |
| MAYW | Maywood & Sugar Creek | 1/80-7/2000 |
| MB | Montpelier & Barre R.R. | 1/75-1/80; eliminated 1/81 |
| Meridian & Bigbee R.R. Co. | 1/75-1/94; eliminated 10/97 | |
| M&B R.R., L.L.C. | added 10/97; 7/2000 | |
| MBBX | Michael D. Boxberger | added 1/80; 1/80; eliminated 1/81 |
| Tank Car Services, Inc. | added 1/81; eliminated 1/86 | |
| MBCX | Material Brokerage Co. | added 10/96; eliminated 7/98 |
| M.B.C.X. Leasing, L.L.C. | added 7/98; 7/2000 | |
| MBFX | MBF Industries, Inc. | added 7/79; 1/80; eliminated 7/91 |
| MBIX | Morse Bros., Inc. | Jul-00 |
| MBKX | MRC Rail Services L.L.C. | added 4/98; added 10/99; 7/2000 |
| MBLX | Mobil Oil Corp. | added 1/95; eliminated 7/2000 |
| Exxon Mobil Corp. | added 7/2000; 7/2000 | |
| MBPX | MacMillan-Bloedel Products, Inc. | added 10/71; eliminated 4/73 |
| MacMillan-Bloedel Inc. | added 4/73; 1/75-1/94; eliminated 1/98; 7/2000 | |
| MBRR | Meridian & Bigbee R.R. Co. | 1/75-1/80 |
| MBSX | M.B. Suydam Co. | Apr-38 |
| M.B. Suydam Division, Pittsburgh Plate Glass Co. | 1/52; eliminated 4/54 | |
| Mid-South Bulk Services, Inc. | added 4/2000; 7/2000 | |
| M&BT | Marianna & Blountstown R.R. | Apr-38 |
| MBT | Marianna & Blountstown R.R. Co. | added 11/73; 1/75-1/80 |
| MBX | Mechling Bros. Chemicals, a Division of General Chemical Co. | Apr-38 |
| MBX | Montrose Beef Co. | 1/52-10/57; eliminated 4/61 |
| MC | Michigan Central R.R. | Jan-75 |
| Consolidated Rail Corp. | Jan-80 | |
| Maine Coast R.R. Corp. | added 10/92; eliminated 10/93; 1/94; eliminated 1/97; added 10/99; 7/2000 | |
| MCAX | Mather Stock Car Co. | 4/38-1/52; eliminated 7/55 |
| North American Car Corp. | added 7/55; 10/57-1/75; eliminated 4/75 | |
| MCCX | Mutual Chemical Co. of America | 4/38-1/52; eliminated 7/55 |
| Mutual Chemical Division, Allied Chemical and Dye Corp. | added 7/55; 10/57 | |
| Madison Coal Corp. | eliminated 7/63 | |
| Mutual Chemical Division, Allied Chemical & Dye Corp. | eliminated 7/58 | |
| Madison Coal Corp. | Apr-61 | |
| Mt. Vernon Coal Transfer Co. | added 1/83; 1/94-7/2000; eliminated 10/2000 | |
| Mt. Vernon Transfer Terminal, LLC | added 10/2000 | |
| MCDX | McDonough Brothers, Inc. | added 7/78; 1/80; eliminated 10/83 |
| Redland Worth Corp. | added 10/83; eliminated 4/86 | |
| Cementos Mexicanos, S.A. | added 4/89; eliminated 7/91 | |
| Sunbelt Cement, Inc. | added 7/91; 1/94-7/2000 | |
| MCER | Massachusetts Central | 1/80-1/94 |
| Massachusetts Central R.R. | added 4/95; 7/2000 | |
| MCEX | Compania Mexicana de Comereio Exterior, S.A. | 1/52-7/65; eliminated 10/65 |
| MCFX | McCall Farm Chemicals, Inc. | eliminated 4/55 |
| MCHX | Merrimac Chemical Co. -- Monsanto Chemical Co., Merrimac Division | Apr-38 |
| Monsanto Chemical Co., Merrimac Division | 1/52; eliminated 4/54 | |
| Monsanto Chemical Co., Everett Plant | added 4/54; eliminated 7/55 | |
| PLM Railcar Maintenance Co. | added 4/85; eliminated 10/89 | |
| Railcar Maintenance Co. | added 10/89; eliminated 4/90 | |
| Transcisco Rail Services Co. | added 4/90; eliminated 1/91 | |
| Transcisco Leasing Co. | added 1/91; 1/94; eliminated 7/97 | |
| Trinity Rail Management, Inc. | added 7/97; 7/2000 | |
| MCIX | Mooney Chemicals, Inc. | added 1/59; 4/61-7/65 |
| Applied Chemicals Division, Mobley Co., Inc. | Jan-80 | |
| SSI Mobley Co., Inc. | added 4/89; eliminated 10/89 | |
| SSI Mobley Co., Inc. (MofW cars) | 1/94-7/2000 | |
| MCLR | McLaughlin Line R.R. | added 7/88; eliminated 1/92; 1/94-7/2000 |
| MCLX | North Western Refrigerator Line Co. | 4/38-1/52 |
| North American Car Corp. | Oct-57 | |
| North Western Refrigerator Line Co. | eliminated 7/58 | |
| Morrison Car Leasing, Inc. | added 4/67; 4/70-1/80 | |
| MCPX | Monsanto Chemical Co. | added 4/62; eliminated 7/64 |
| Monsanto Co. | added 7/64; 7/65-1/94; eliminated 1/98 | |
| Solutia Inc. | added 1/98; 7/2000 | |
| MCR | McCloud River Ry. Co. | 1/75-1/80 |
| McCloud Ry. Co. | 1/94-7/2000 | |
| MCRR | The Monongahela Connecting R.R. Co. | 1/75-7/2000 |
| MCRX | McCook Rendering Plant | Jan-52 |
| McCook Rendering Co. | 10/57; eliminated 1/58 | |
| Marcus Rail Transport, L.L.C. | Jul-00 | |
| MC&S | Moscow, Camden & San Augustine R.R. | Apr-38 |
| MCSA | Moscow, Camden & San Augustine R.R. | 1/75; added 7/79; 1/80; 1/94; eliminated 1/2000; 7/2000 |
| MCSX | Mells Cargo Supply, Inc. | Jan-94 |
| MCTA | Minnesota Central R.R. Co. | added 4/95; eliminated 4/97; 7/2000 |
| MCTR | Mackinac Transportation Co. | Jan-75 |
| MCTX | Michigan Chemical Corp. | 10/57-1/75 |
| Velsicol Chemical Corp. | 1/80; eliminated 7/82 | |
| Modern Continental Construction Co. Inc. | Jul-00 | |
| MCVX | Massachusetts Call/Volunteer Firefighters Association | Jul-00 |
| MCWX | Morton Chemical Co. | 4/61; eliminated 4/62 |
| Morton Salt Co. | added 4/62; eliminated 7/65 | |
| Morton International, Inc. | added 7/65; 7/65-10/66; eliminated 7/69 | |
| MCX | The Mead Corporation | 4/38-1/52 |
| MD | Municipal Docks Ry. of the Jacksonville Port Authority | Jan-75 |
| Municipal Docks | Jan-80 | |
| MDAX | Merchants Despatch Transportation Co. | added 1/62; 7/65-1/80 |
| MDCX | Middleboro Chemical Industries, Inc. | 4/70; eliminated 1/72 |
| Mexicana de Cobre, S.A. de C.V. | added 7/89; 1/94-7/2000 | |
| MDDE | Maryland and Delaware R.R. Co. | added 1/78; 1/80; eliminated 10/87; 1/94-7/2000 |
| MDDX | Old Line Holding Co., Inc. | Jul-00 |
| MDFX | Merchants Despatch Transportation Co. | added 1/62 |
| MDIX | Modern Dispersions, Inc. | Jul-00 |
| MDKX | Mandak Metal Processors Division of Gerdau MRM Steel Inc. | Jul-00 |
| MDLR | The Midland Terminal Co. | added 10/83; 1/94-7/2000 |
| MDP | Mexican Pacific R.R. Co., Inc. (Ferrocarril Mexicano del Pacifico, S.A.) | 1/75-1/80 |
| Mexican Pacific R.R. Co., Inc. (transferred to Ferrocarriles Nacionales de Mexico) | eliminated 10/88 | |
| MDR | MidLouisiana Rail Corp. | added 1/88; 1/94; eliminated 7/94 |
| Kansas City Southern Ry. Co. | added 7/94; 7/2000 | |
| MDRY | Madison Ry. Co., Inc. | added 1/78; eliminated 1/79 |
| MD&S | Macon, Dublin & Savannah R.R. Co. | 4/38-10/57 |
| MDS | Meridian Southern Ry., L.L.C. | Jul-00 |
| MDSB | Burlington Northern Inc. | Jan-80 |
| MDSX | Merchants Despatch Transportation Co. | added 7/55 |
| MDT | Merchants Despatch Transportation Co. | 4/38-1/80; eliminated 1/83 |
| MDTX | Merchants Despatch Transportation Corp. | added 7/89; 1/94; eliminated 7/99 |
| Southern Region Industrial Realty, Inc. | added 7/99; 7/2000 | |
| MDW | Minnesota, Dakota & Western Ry. Co. | 1/75-7/2000 |
| ME | Mississippi Eastern Ry. | 4/38-1/52 |
| Morristown & Erie R.R. Co. | 1/75-1/80; added 1/86; eliminated 1/88 | |
| Morristown & Erie Ry., Inc. | added 1/88; 1/94-7/2000 | |
| MEC | Maine Central R.R. Co. | 4/38-1/94; eliminated 4/97; added 7/98; 7/2000 |
| MECX | Transcisco Leasing Co. | added 7/94; eliminated 7/97 |
| Trinity Rail Management, Inc. | added 7/97; 7/2000 | |
| MELX | Melwire Inc. | eliminated 4/91 |
| Sunbelt Cement, Inc. | added 4/91; eliminated 7/91; 1/94-7/2000; added 10/2000 | |
| MEPX | McGraw-Edison Co. | added 4/69; 4/70-1/80; eliminated 10/93; 1/94-7/2000 |
| MERW | Mercersburg Ry., Inc. | added 4/79; 1/80; added 7/80; eliminated 1/81 |
| MERX | Mercantile Refrigerator Line (Merchants Despatch Transportation Corp.) | 1/52-10/57 |
| Merchants Despatch Transportation Co. | 4/61-4/70; eliminated 1/73 | |
| Merco, A Joint Venture | 1/94; added 1/97; 7/2000 | |
| MESX | Mears/CPG, Inc. | added 7/98; 7/2000 |
| MET | Modesto and Empire Traction Co. | 1/75-7/2000 |
| METC | Modesto & Empire Traction Co. | 4/38-10/66; eliminated 7/74 |
| METW | Municipality of East Troy, Wisc. | 1/75-7/2000 |
| METX | Northeast Illinois Regional Commuter R.R. Corp. | added 10/96; 7/2000 |
| MF | Middle Fork | 1/75-1/80 |
| MFCX | Marfax Steel and Railway Equipment Co. | added 10/67; 4/70; eliminated 7/70 |
| Farmers Coop Grain and Supply Co. | added 7/80; eliminated 4/89 | |
| Chrysler Rail Transportation Corp. | eliminated 4/93 | |
| U.S. Rail Services, Inc. | added 4/93; 1/94; eliminated 4/94 | |
| USL Capital Rail Services | added 4/94; eliminated 10/96 | |
| First Union Rail | added 10/96; 7/2000 | |
| MFFX | Midwestern Farm Fertilizers, Inc. | 4/61-7/65; eliminated 10/65 |
| M4 Holdings Ltd. | added 4/85; eliminated 1/92; 1/94-7/2000 | |
| MFLX | McColl-Frontenac Oil Co., Ltd. | 4/38-1/52 |
| MFNX | Morlunda Farms, Oscar Nelson, Inc. | added 4/65; added 1/67 |
| Morlunda Farms | Apr-70 | |
| MFVX | Merchants Despatch Transportation Corp. | added 4/65; 7/65-1/75; eliminated 4/76; 1/80 |
| MG | Mobile & Gulf R.R. Co. | 1/75-1/80 |
| MGA | Monongahela Ry. Co. | 4/38-10/66 & 1/75-1/80; eliminated 7/93 |
| Consolidated Rail Corp. | added 7/93; 1/94; eliminated 7/99 | |
| Norfolk Southern Ry. Co. (Norfolk Southern) | Jul-00 | |
| MGAC | Monongahela Connecting R.R. Co. | 7/65-10/66 |
| MGCX | Morrison Grain Co. | added 1/67; eliminated 4/67 |
| MGLX | McGoldrick Lumber Co. | Apr-38 |
| MGMX | J and J Leasing | added 4/89; eliminated 10/89 |
| J and J Partnership | added 10/89; eliminated 10/93; 1/94-7/2000 | |
| MGPX | L.M. Martini Grape Products | Apr-38 |
| MGRI | MG Rail, Inc. | 1/94-7/2000 |
| MGRS | Ferrocarrils Nacionales de Mexico (National Rys. of Mexico) | 1/75-1/80 |
| MGSX | Martin Gas Sales, Inc. | added 1/81; 1/94-7/2000; eliminated 4/2001 |
| MGSX | CF Martin Sulphur, LP | added 4/2001 |
| MH | Mount Hood Ry. Co. | 1/75-1/80; eliminated 1/89 |
| Mount Hood R.R. | added 1/89; eliminated 10/89 | |
| Mount Hood R.R. Co. | Jul-00 | |
| MHAX | U.S. Dept. of the Interior, Bureau of Mines Helium Activity | added 7/55 |
| U.S. Dept. of the Interior, Bureau of Mines | 10/57-7/65 | |
| U.S. Dept. of the Interior, Bureau of Mines Helium Activity | Oct-66 | |
| U.S. Dept. of the Interior, Bureau of Mines | Apr-70 | |
| U.S. Dept. of the Interior, Bureau of Mines, Helium Operations | 1/75-1/80 | |
| U.S. Dept. of the Interior, Bureau of Mines, Helium Operations, Amarillo, Texas | eliminated 7/80 | |
| U.S. Dept. of the Interior, Bureau of Mines, Helium Field Operations, Amarillo, Texas | added 7/80; eliminated 10/81 | |
| U.S. Dept. of the Interior, Bureau of Mines, Division of Helium Operations, Amarillo, Texas | added 10/81; eliminated 7/82 | |
| U.S. Dept. of the Interior, Bureau of Mines, Helium Field Operations, Amarillo, Texas | added 7/82; 1/94 | |
| U.S. Dept. of the Interior, Bureau of Land Management, Helium Opers | eliminated 10/98 | |
| U.S. Dept. of the Interior, Bureau of Mines, Helium Field Operations, Amarillo, Texas | Jul-00 | |
| MHCO | Marquette & Huron Mountain R.R. Co., Inc. | 1/75-1/80 |
| MHFX | MHF Logistical Solutions Inc. | added 10/98; 7/2000 |
| MHLX | Union Refrigerator Transit Lines | added 1/62; 7/65 |
| Union Refrigerator Transit Lines, Division of General American Transportation Corp. | Oct-66 | |
| Union Refrigerator Transit Lines | Apr-70 | |
| Union Refrigerator Transit Lines, Division of General American Transportation Corp. | eliminated 10/71 | |
| General American Transportation Corp., Freight Car Division | added 10/71 | |
| General American Transportation Corp. | 1/75-1/80; eliminated 10/92 | |
| MHM | Mount Hope Mineral R.R.Co. | Jan-75 |
| Consolidated Rail Corp. | Jan-80 | |
| MHMX | Miner-Hillard Milling Co. | 7/65-10/66; eliminated 4/67 |
| MHRR | Mahanoy and Hazleton Ry., Inc. | eliminated 10/86 |
| MHRX | Mile-High Railcar Leasing, Inc. | added 1/80; 1/80; eliminated 1/88 |
| Mile-High Railcar Services, Inc. | added 1/88; eliminated 1/93; eliminated 4/93; 1/94-7/2000 | |
| MHSX | Midvale-Heppenstall Co. | added 10/65; 10/66-4/70; eliminated 1/71 |
| MHTX | Mangels, Herold Co., Inc. | 4/38-10/57 |
| MHWA | Mohawk, Adirondack & Northern R.R. Corp. | 1/94; added 1/96; 7/2000 |
| MHZX | Matthieson & Hegeler Zinc Co. | 4/38-1/52 |
| MI | Minnesota & International Ry. Co. | Apr-38 |
| Missouri-Illinois R.R. Co. | 10/57-10/66 & 1/75 | |
| Missouri Pacific R.R. Co. | Jan-80 | |
| Missouri Pacific System | 1/94; eliminated 4/97 | |
| Union Pacific R.R. Co. | added 4/97; 7/2000 | |
| MICO | Midland Continental R.R. | Oct-66 |
| MICX | Mississippi Chemical Corp. | 1/52-4/70 |
| MICX | Mis Coa, a partnership of Mississippi Chemical Corp. and Coastal Chemical Corp. | eliminated 10/72 |
| Mississippi Chemical Corp. | added 10/72; 1/75-1/80; eliminated 10/81 | |
| MID | Midway R.R. Co. | Jan-75 |
| Midway | Jan-80 | |
| MIDH | Middletown & Hummelstown R.R. Co. | 1/80-7/2000 |
| MIDX | Merchants Despatch Transportation Co. | 7/65-4/70; eliminated 1/73 |
| Midwest Energy Services Co. | added 4/89; 1/94 | |
| Unitrain, Inc. | added 1/94; eliminated 4/98 | |
| MRC Rail Services, LLC | added 4/98; 7/2000 | |
| MIGN | Michigan Northern Ry. Co., Inc. | eliminated 1/79; 1/80; eliminated 4/89 |
| MILW | Chicago, Milwaukee, St. Paul and Pacific R.R. Co. | 1/52-10/66 & 1/75-1/80; eliminated 1/81 |
| Chicago, Milwaukee, St. Paul and Pacific R.R. Co. (Richard B. Ogilvie, Trustee) | added 1/81 | |
| The Milwaukee Road | eliminated 4/86 | |
| Soo Line R.R. Co. | 1/94-7/2000 | |
| MILX | Milchem Inc. | added 4/82; eliminated 7/88 |
| Milpark Drilling Fluids | added 7/88; eliminated 7/93 | |
| General Electric Railcar Services Corp. | added 7/93; 1/94; eliminated 1/2000 | |
| General Electric Rail Services Corp. | added 1/2000; 7/2000 | |
| MIMX | Minera Mexico Internacional, Inc. | added 7/78; 1/80; eliminated 7/87; 1/94-7/2000 |
| MINE | Minneapolis Eastern Ry. Co. | 1/75-1/80 |
| MINX | Minnesota Mining and Manufacturing Co., Inc. | 1/52-10/66; eliminated 4/68 |
| MIPX | Millennium Petrochemicals, Inc. | 7/2000; eliminated 4/2001 |
| MIR | Minneapolis Industrial Ry. Co. | 4/61-10/66 & 1/75-1/80; eliminated 1/85 |
| MIRX | Mindis Recycling | added 1/97 |
| Regional Recycling, L.L.C. | Jul-00 | |
| MIS | Mississippi Central R.R. Co. | 1/94-7/2000 |
| MISS | Mississippian | 1/75-1/80 |
| The Mississippian Ry., Inc. | added 1/81; eliminated 1/87 | |
| The Mississippian Ry. Cooperative, Inc. | added 1/87; 1/94-7/2000 | |
| MISX | Milwaukee Solvents & Chemicals Corp. | added 1/74; 1/75-7/2000 |
| MITX | Interall Holdings, Inc. | added 10/60; 4/61 |
| MIW | Tomahawk Ry., Limited Partnership | eliminated 4/95 |
| MJ | Manufacturers' Junction Ry. Co. | 4/38-7/2000 |
| MKC | McKeesport Connecting R.R. Co. | 1/52-7/2000 |
| MKCX | Morrison Knudsen Corp. | Jul-00 |
| MKGX | North American Car Corp. | added 10/60; 4/61-1/75 |
| MKIX | Morrison-Knudsen Co., Inc. | added 10/71; 1/75 |
| M-K Railroad Equipment Leasing Co., Inc. | 1/80; eliminated 4/89; 1/94 | |
| Morrison Knudsen Corp. | Jul-00 | |
| MKPX | Meyer Kornblum Refrigerator Car Co. | Apr-38 |
| M-K-T | Missouri-Kansas-Texas R.R. Co. | Apr-38 |
| MKT | Missouri-Kansas-Texas R.R. Co. | 1/52-10/66 & 1/75-1/80; eliminated 1/90 |
| Missouri Pacific System | added 1/90; 1/94; eliminated 4/97 | |
| Union Pacific R.R. Co. | added 4/97; 7/2000 | |
| MKTT | Missouri-Kansas-Texas R.R. Co. of Texas | 4/38-4/61 |
| Missouri-Kansas-Texas R.R. Co. | 7/65-10/66 & 1/75-1/80; eliminated 1/90 | |
| Missouri Pacific System | added 1/90; 1/94; eliminated 4/97 | |
| Union Pacific R.R. Co. | added 4/97; 7/2000 | |
| MLCX | American Refrigerator Transit Co. | added 7/70; 1/75-7/2000 |
| MLD | Midland Ry. Co. of Manitoba | 4/38-10/66 |
| Midland | 1/75-1/80 | |
| MLEX | Bulk Equipment Specialist | Jan-94 |
| Miles Inc. | Jul-00 | |
| MLHX | Missouri Improvement Co. | added 10/71; 1/75-1/80 |
| MLKX | Milk Products Refrigerater Line (Merchants Despatch Transportation Corp.) | Apr-38 |
| Merchants Despatch Transportation Co. | 1/52-4/70; eliminated 10/70 | |
| MLLX | Montell U.S.A., Inc. | added 4/96; 7/2000; eliminated 1/2001 |
| Basell U.S.A., Inc. | added 1/2001 | |
| MLMX | Morrison Grain Co., Inc. | added 7/74; 1/75-1/80; eliminated 4/87 |
| MLR | Mineral Range R.R. Co. | 4/38-1/52 |
| MLS | Manistique & Lake Superior R.R. | 4/38-10/66 |
| MLST | Milstead | 1/75-1/80 |
| MLSX | Monsanto Co. | added 10/97; added 1/98; 7/2000 |
| ML&T | Morgan's Louisiana & Texas R.R. | 4/38-1/52 |
| MLUX | Monsanto Chemical Co. | added 7/59; 4/61; eliminated 7/64 |
| Monsanto Co. | added 7/64; 7/65-1/94; eliminated 1/98 | |
| Solutia Inc. | added 1/98; 7/2000 | |
| MLWX | MLWX Co. | 1/52-10/57; eliminated 7/60 |
| MLX | Master Lubricants Co. | 4/38-4/61; eliminated 7/63 |
| MMAX | Martin Marietta Aluminum Inc. | added 7/82; eliminated 1/85 |
| Martin Marietta Corp. | added 4/85; 1/94; eliminated 7/97; 7/2000 | |
| MMBX | Martin Marietta Corp. | added 1/79; 1/80; eliminated 7/86 |
| Master Builders, Inc. | added 10/87; 1/94; eliminated 10/95; added 10/96; eliminated 1/97; 7/2000 | |
| MMCX | North American Car Corp. | 4/61-4/70; eliminated 1/72 |
| MMCX | M & M Chemical Products, Inc. | added 7/77; 1/80; eliminated 7/89 |
| TransMatrix, Inc. | added 7/89; 1/94-7/2000 | |
| MMGX | Stanolind Oil & Gas Co. | Apr-38 |
| MMID | Maryland Midland Ry., Inc. | added 1/81; added 4/81; 1/94-7/2000 |
| MMIX | Metal-Matic, Inc. | added 7/73; 1/75-1/80; eliminated 4/84 |
| MMMX | Minnesota Mining & Manufacturing d/b/a 3M | Jul-00 |
| MMRR | Mid-Michigan R.R., Inc. | added 4/88; 1/94-7/2000 |
| MMRX | Double M Ranch Enterprises | 1/94-7/2000 |
| MMSX | Martin Marietta Cement, Division of Martin Marietta Corp. | added 1/75; 1/75; eliminated 1/79 |
| Martin Marietta Corp. | added 1/79; 1/80 | |
| Blue Circle Inc. | eliminated 4/87 | |
| MMX | Mosinee Paper Mills Co. | Apr-38 |
| Monarch Molasses Co. | 1/52; eliminated 1/53 | |
| M&NA | Missouri & Northern Arkansas Ry. Co. | Apr-38 |
| MNA | Missouri & Northern Arkansas R.R. Co., Inc. | added 4/93; 1/94-7/2000 |
| MNAX | C&S Directional Boring, Inc. | Jul-00 |
| MNBR | M&B R.R., L.L.C. | added 10/97; 7/2000 |
| MNCW | Metro-North Commuter R.R. | 1/94-7/2000 |
| MNCX | Maintenance Inc. | 10/57-4/61; eliminated 4/62 |
| Minnesota Corn Processors, Inc. | added 4/85; 1/94-7/2000; eliminated 10/2000 | |
| M&NE | Manistee & Northeastern Ry. Co. | 4/38-1/52 |
| MNJ | Middletown and New Jersey Ry. Co., Inc. | 1/75; added 4/78; 1/80-7/2000 |
| MNL | Mountain Laurel R.R. Co. | Jan-94 |
| MNLX | Exxon Mobil Corp. | Jul-00 |
| MNN | Minnesota Northern R.R., Inc. | 7/2000; added 4/2001 |
| MNNR | Minnesota Commercial Ry. Co. | added 4/87; 1/94-7/2000 |
| MNPX | Morton Salt Co. | added 7/80; eliminated 7/81 |
| Morton Salt-Division Norwich Products, Inc. | added 7/81; eliminated 10/81 | |
| Morton Salt-Division of Morton Norwich Products, Inc. | added 10/81; eliminated 4/87 | |
| Morton Salt-Division of Morton Thiokol, Inc. | added 4/87; 1/94; eliminated 4/97 | |
| Morton International, Inc. | added 4/97; 7/2000 | |
| MNR | Burlington Northern Inc. | 1/80; eliminated 4/81 |
| MNS | Minneapolis, Northfield and Southern Ry. | 1/52-10/66 & 1/75-1/80; eliminated 4/80 |
| Minneapolis, Northfield and Southern Ry., Inc. | added 4/80; eliminated 4/86 | |
| Soo Line R.R. Co. | 1/94-7/2000 | |
| MNVA | Minnesota Valley Transportation Co., Inc.-Southwest | added 7/84; eliminated 10/90 |
| MNVA R.R., Inc. | added 10/90; 1/94; eliminated 4/95 | |
| MNWX | Minnesota Dept. of Public Service Weights and Measures Division | added 7/93; 1/94; eliminated 10/99; 7/2000 |
| MNX | National Car Co. | 1/52; eliminated 7/56 |
| Burlington Refrigerator Express Co. | added 7/56 | |
| National Car Co. | 10/57-4/70; eliminated 1/72 | |
| Western Fruit Express Co. | added 1/72; 1/75-1/80; eliminated 1/81 | |
| MOBX | Socony Mobil Oil Co., Inc. | 4/61-7/65 |
| Mobil Oil Co., a Division of Socony Mobil Oil Co., Inc. | eliminated 10/66 | |
| Mobil Oil Corp. | added 10/66; 10/66-1/94; eliminated 7/2000 | |
| Exxon Mobil Corp. | added 7/2000; 7/2000 | |
| MOC | Missouri Central R.R. Co. | Jul-00 |
| MOCX | Missouri Portland Cement Co. | 1/52-1/80; eliminated 10/84 |
| MOD | Texas and Pacific Railway Co. | 1/75; eliminated 1/77 |
| Missouri Pacific Railroad Co. | added 1/77; 1/80 | |
| Missouri Pacific System | eliminated 10/81; eliminated 5/83 | |
| MODX | American Refrigerator Transit Co. | added 7/55; 10/57-1/75; eliminated 7/77 |
| MOEX | Morgan Engineering Co. |