| K & D Salvage Co. | KNDX | added 1/73; 1/75; eliminated 4/76 | |
| K&W Trucking Co., Inc. | KWTX | Jan-94 | |
| K.A. Powell (Canada) Ltd. | KAPX | added 10/53; 10/57; eliminated 7/58 | |
| K.R. D-X Co. | KRDX | added 7/67; 4/70-1/80; eliminated 4/88 | |
| K.W.T. Ry., Inc. | KWT | added 7/87; 1/94-7/2000 | |
| Kaber Co. | KABX | 1/75; added 4/75; 1/80; eliminated 7/93 | |
| KABX | Jan-94 | ||
| Kaiser Aluminum & Chemical Corp. | KACX | 4/61-1/94; eliminated 7/94; 7/2000 | |
| Kaiser Cement & Gypsum Corp. | KCGX | added 10/65; 10/66-1/75; eliminated 1/80 | |
| Kaiser Cement Corp. | KCGX | added 1/80; 1/80; eliminated 1/90 | |
| Kaiser Steel Corp. | KSCX | 1/52; added 7/66; 10/66-1/75; eliminated 7/78 | |
| kalamazoo Rendering Works | KRWX | 1/52; eliminated 4/55 | |
| kalamazoo Rendering Works, Inc. | KRWX | added 4/55; 10/57; eliminated 10/59 | |
| Kalamazoo, Lake Shore & Chicago Ry. | KLSC | 1/94-7/2000 | |
| Kamen, Inc. | KAMX | added 4/85; 1/94-7/2000 | |
| Kanawha Rail Corp. | WNFR | added 10/2000 | |
| Kankakee, Beaverville and Southern R.R. Co. | KBSR | added 4/78; 1/80-7/2000 | |
| Kanotex Refining Co. | APOX | eliminated 10/53 | |
| Kansas and Missouri Ry. and Terminal Co. | KM | 1/94-7/2000 | |
| Kansas City Connecting R.R. Co. | KCC | 1/75-1/80 | |
| Kansas City Power & Light Co. | KCLX | added 4/71; 1/75-1/94; eliminated 7/97; 7/2000 | |
| Kansas City Southern Ry. Co. | KCS | 7/65-7/2000 | |
| CCR | added 7/94; 7/2000 | ||
| GMSR | added 7/94; 7/2000 | ||
| GNA | added 10/93; 1/94-7/2000 | ||
| MDR | added 7/94; 7/2000 | ||
| MSRC | added 7/94; 7/2000 | ||
| NLG | added 7/94; 7/2000 | ||
| SR | added 7/94; 7/2000 | ||
| TNR | added 7/94; 7/2000 | ||
| Kansas City Terminal Ry. Co. | KCT | 4/38-1/75; eliminated 1/86; 1/94; eliminated 1/95 | |
| Kansas City Westport Belt | KCWB | 1/75-1/80 | |
| Kansas City, Kaw Valley & Western R.R. | KVW | 4/38-10/57 | |
| Kansas City, Kaw Valley R.R. Inc. | KVW | Apr-61 | |
| Kansas City, Mexico & Orient | KCMO | 1/75-1/80 | |
| Kansas Eastern R.R. Inc. | KE | Jul-00 | |
| Kansas Southwestern Ry. | KSW | added 4/92; 1/94-7/2000; eliminated 4/2001 | |
| Kaolin Mushroom Farms, Inc. | KMFX | added 1/74; 1/75 | |
| Kasgro Rail Corp. | KGRX | added 10/96; 7/2000 | |
| Kasgro Rail Lines | KRL | added 10/2000 | |
| Kaw Paving Co. | KPX | 1/52-4/61 | |
| KCAC, Inc. | KCAX | eliminated 1/87 | |
| KCT Ry. Corp. | KCTV | added 7/90; eliminated 7/92; 1/94-7/2000 | |
| KDEX Leasing Co. | KDEX | added 10/86; eliminated 1/88 | |
| Keefe Packing Co. (Merchants Despatch Transportation Corp.) | KRCX | Apr-38 | |
| Keilman Brothers | KMBX | Oct-57 | |
| Keith Railway Equipment Co. | NRNX | Jan-52 | |
| PTSX | 1/52; eliminated 10/53 | ||
| Keith Ry. Equipment Co. | KTX | 1/52-4/61 | |
| Keith Tank Line (Keith Ry. Equipment Co.) | KTX | Apr-38 | |
| Kelley's Creek & Northwestern R.R. Co. | KCNW | 1/75-1/94 | |
| Kellogg Company | KELX | added 7/81; 1/94-7/2000 | |
| Kemira Chemicals Canada Inc. | KCPX | added 7/99; 7/2000 | |
| Kendall Refining Co. | KRTX | Apr-38 | |
| Kennecott Co. R.R. | KENN | 1/80-7/2000 | |
| Kennecott Copper Corp. | KCCX | added 4/70; 4/70-1/80; eliminated 4/81 | |
| Kennecott Corp. | KCCX | added 4/81; eliminated 4/91 | |
| Kennecott Utah Copper Corp. | KCCX | added 4/91; 1/94-7/2000 | |
| Kent, Barry, Eaton Connecting Ry., Inc. | KBEC | added 4/80 | |
| Kentucky & Indiana Terminal R.R. Co. | KIT | 1/75-1/80; eliminated 4/82 | |
| Kentucky & Tennessee Ry. Co. | KT | 4/38-1/80; eliminated 10/93; 1/94-7/2000 | |
| Kentucky Independent Packing Co., Inc. (National Car Co.) | KIPX | Apr-38 | |
| Kentucky May Coal Co., Inc. | ELSX | added 1/90; 1/94; eliminated 7/98; 7/2000 | |
| Kentucky Processing Co. | KPGX | added 1/97; eliminated 1/99; 7/2000 | |
| Kentucky Utilities Co. | KUCX | added 7/76; 1/80; eliminated 4/91; added 10/92; 1/94-7/2000 | |
| Kentucky-Tennessee Clay Co. | AMMX | added 7/90; 1/94-7/2000 | |
| KENX Associates | KENX | added 4/78; 1/80 | |
| Keokuk Canning Co. | KKCX | Apr-38 | |
| Keokuk Junction Ry. | KJRY | added 4/82; 1/94-7/2000 | |
| Keokuk Northern Real Estate Co. (d/b/a Keokuk Junction Ry.) | KJRY | added 1/82; eliminated 4/82 | |
| Keota Washington Transportation Co. | KWTR | added 1/82 | |
| Kerford Limestone Co. | KLSX | added 7/80; eliminated 10/84 | |
| Kerley Industries, Inc. | KIIX | added 10/84; eliminated 7/89 | |
| Kerr-McGee Chemical Corp. | KMCX | reporting marks changed from APMX 1/71; eliminated 11/73; 1/80; eliminated 4/93; added 10/93; 1/94; eliminated 1/95 | |
| Kerr-McGee Coal Corp. | KMCX | added 1/95; eliminated 7/98; 7/2000 | |
| Kerr-McGee Oil Industries, Inc. | KRMX | added 7/56; 10/57-4/61 | |
| Kershaw Manufacting Co. | KMUX | 1/94-7/2000 | |
| Ketchikan Pulp Co. | PBBX | added 10/68; 4/70-1/75 | |
| Kewaunee, Green Bay & Western R.R. Co. | KGB | 4/38-10/66 | |
| Keywell Corp. | KEYX | 1/94-7/2000 | |
| Kiamichi R.R. Co., Inc. | KRR | added 1/88; 1/94; eliminated 10/96 | |
| Kiamichi R.R. Co., L.L.C. | KRR | added 10/96; 7/2000 | |
| Kidd Creek Mines, Ltd. | KCMX | added 4/82; eliminated 7/86 | |
| Kimberly-Clark Co. | KCCX | 4/38-4/61 | |
| Kimberly-Clark Corp. | WBLX | eliminated 4/65 | |
| Kimberly-Clark of Canada Ltd. | KCWX | added 7/77; 1/80; eliminated 1/94; 7/2000 | |
| Kimberly-Clark of Michigan, Inc. | WBLX | added 4/55; 10/57-4/61 | |
| Kingan Refrigerator Line | KRLX | Apr-38 | |
| Kingcome Navigation | KNC | Jan-75 | |
| KNC | 1/80-7/2000 | ||
| Kingsford Chemical Co. | KCX | eliminated 10/57 | |
| Kingsford Co. | KCX | added 10/57; 10/57-4/61; eliminated 1/62 | |
| Kingston Terminal R.R. Corp. | KTER | added 7/80; eliminated 10/80 | |
| Kingwood Northern d/b/a West Virginia Northern R.R., Ltd. | WVN | Jul-00 | |
| Kirby Refining Co. | KYCX | eliminated 7/56 | |
| Klamath Gas Co. | KTCX | added 7/63; 7/65-1/75; eliminated 1/80 | |
| Klamath Northern Ry. Co. | KNOR | 1/75-1/80 | |
| Knappen Milling Co. | KMCX | added 7/64; 7/65-10/66; eliminated 7/68 | |
| Knauf Fiber Glass, GmbH | KFGX | added 4/78; 1/80; eliminated 7/87; 1/94-7/2000 | |
| KND Rail Services, Inc. | KNDX | added 1/97; 7/2000; eliminated 7/2001 | |
| Knox & Kane R.R. Co. | KKRR | added 10/82; 1/94-7/2000 | |
| Knox Kershaw Co., Inc. | RKCX | added 1/69; 4/70-1/80; eliminated 4/85; 1/94-7/2000 | |
| Knox Metals Corp. | KNOX | added 1/96; eliminated 4/97; 7/2000 | |
| Knoxville & Holston River R.R. Co., Inc. | KXHR | added 10/98; 7/2000 | |
| AGLF | added 7/99; 7/2000 | ||
| Koch Tank Line, Inc. | OFKX | 4/38-10/66; eliminated 1/67 | |
| Kodak Canada, Inc. | KDCX | added 10/90; 1/94; eliminated 1/95 | |
| Kohrs Packing Co. (cars no. 2601-2621) (National Car Co.) | KOHX | Apr-38 | |
| Kohrs Packing Co. (cars no. 3100-3150) (Mather Stock Car Co.) | KOHX | Apr-38 | |
| Kootenay Central Rail Services Ltd. | KCRX | Jul-00 | |
| Koppel, Inc. | KPLX | 1/80; eliminated 1/85 | |
| Koppers Co. | SBPX | Apr-38 | |
| Koppers Co., Inc. | KCIX | added 1/65; 7/65; eliminated 4/66 | |
| KFPX | added 10/69; 4/70-1/80; eliminated 10/87 | ||
| KGCX | added 4/55; 10/57-1/80; eliminated 10/89 | ||
| KOPX | 4/38-1/52 | ||
| KPCX | 4/38-1/80; eliminated 10/89 | ||
| DYLX | added 7/59 | ||
| DYLX | eliminated 1/62 | ||
| Koppers Industries, Inc. | KIIX | added 7/97; 7/2000 | |
| KPCX | added 10/89; 1/94-7/2000 | ||
| Korf Transport Corp. | KTIX | added 7/75 | |
| Kosmos Cement Co., Inc. | KSMX | added 4/81; eliminated 1/89 | |
| Kosmos Portland Cement Co. | KSMX | 1/52-4/70; eliminated 4/72 | |
| Kraft Foods, a Division of National Dairy Products Corp. | KRFX | added 7/58; eliminated 4/61; eliminated 1/62 | |
| Kuner-Empson Co. | KECX | 4/38-1/52 | |
| KVP Co., Ltd. | KVPX | 1/52-10/66; eliminated 4/67 | |
| Kyle R.R. Co. | KYLE | added 4/82; added 1/86; 1/94-7/2000 | |
| Kyle Rys., Inc. | KRIX | added 4/96; eliminated 10/98 | |