| 1 | P&E | Consolidated Rail Corp. | added 4/1976 | | NAKINA |
| 2 | P&E | Penn Central Transportation Co., Robert W. Blanchette, Richard C. Bond and John H. McArthur, Trustees | eliminated 4/1976 | | NAKINA |
| 3 | P&E | Penn Central Transportation Co., Robert W. Blanchette, Richard C. Bond and John H. McArthur, Trustees | eliminated 4/76 | | NRHS |
| 4 | P&E | Consolidated Rail Corp. | added 4/76 | | NRHS |
| 5 | P&E | CONSOLIDATED RAIL CORP. [PENN CENTRAL TRANSPORTATION CO.; PEORIA & EASTERN RY.] | | | PWRC |
| 6 | P&IN | Pacific and Idaho Northern Ry. (Co.) | 8/1920-7/1936 | | NAKINA |
| 7 | P&IN | PACIFIC & IDAHO NORTHERN RWY. | | | PWRC |
| 8 | P&LE | PITTSBURGH & LAKE ERIE RAILROAD (NOW CSX TRANSPORTATION) | | | PWRC |
| 9 | P&MP | Paris & Mt. Pleasant R.R. Co. | 8/1920-7/1936 | | NAKINA |
| 10 | P&MP | PARIS & MT. PLEASANT RAILROAD CO. | | | PWRC |
| 11 | P&N | Seaboard Coast Line R.R. Co. | eliminated 4/1975 | | NAKINA |
| 12 | P&N | Seaboard Coast Line R.R. Co. | eliminated 4/75 | | NRHS |
| 13 | P&N | SEABOARD COAST LINE RAILROAD CO. [PIEDMONT & NORTHERN RWY.] | | | PWRC |
| 14 | P&NW | (The) Prescott & Northwestern R.R. (Co.) | 7/1923-10/1966 | | NAKINA |
| 15 | P&NW | Prescott & Northwestern R.R. | 4/38-10/66 | | NRHS |
| 16 | P&NW | PRESCOTT & NORTHWESTERN RAILROAD CO. | | | PWRC |
| 17 | P&OV | Pittsburgh & Ohio Valley Ry. | 4/1938-10/1966 | | NAKINA |
| 18 | P&OV | Pittsburgh & Ohio Valley Ry. Co. | 7/1923-7/1936 | | NAKINA |
| 19 | P&OV | Pittsburgh & Ohio Valley Ry. | 4/38-10/66 | | NRHS |
| 20 | P&OV | PITTSBURGH & OHIO VALLEY RAILWAY CO. | | | PWRC |
| 21 | P&PU | Peoria & Pekin Union Ry. | 8/1920-4/1970 | | NAKINA |
| 22 | P&PU | Peoria & Pekin Union Ry. | 4/38-4/70 | | NRHS |
| 23 | P&PU | PEORIA & PEKIN UNION RAILWAY CO. | | | PWRC |
| 24 | P&R | Philadelphia & Reading Ry. Co. (Reading Co.) | 7/1930-7/1936 | | NAKINA |
| 25 | P&R | Philadelphia & Reading Ry. Co. | 8/1920-7/1923 | | NAKINA |
| 26 | P&R | READING CO. [PHILADELPHIA & READING RAILWAY CO.] | | | PWRC |
| 27 | P&SR | Petaluma & Santa Rosa R.R. | 4/1938-4/1970 | | NAKINA |
| 28 | P&SR | Petaluma & Santa Rosa R.R. | 4/38-4/70 | | NRHS |
| 29 | P&SR | PETALUMA & SANTS ROSA RAILROAD CO. | | | PWRC |
| 30 | P&WRR | PIEDMONT & WESTERN RAILROAD CLUB (OLD ROCK SCHOOL RAILWAY MUSEUM) | | | PWRC |
| 31 | P&WV | Norfolk and Western Ry. Co. | 10/1966 | | NAKINA |
| 32 | P&WV | Pittsburgh & West Virginia Ry. (Norfolk and Western Ry.) | 4/1970 | | NAKINA |
| 33 | P&WV | (The) Pittsburgh & West Virginia Ry. (Co.) | 8/1920-7/1965 | | NAKINA |
| 34 | P&WV | PITTSBURGH & WEST VIRGINIA RY (NOW NORFOLK SOUTHERN RAILWAY) | | | PWRC |
