The Southern Pacific (reporting mark SP) (or Espee from the railroad initials- SP) was a name of multiple American Class I railroads that existed from 1865 to 1998 and all operated in the Western United States. The names that represented the Southern Pacific were Southern Pacific Railroad, Southern Pacific Companyand Southern Pacific Transportation Company.

The original Southern Pacific began in 1865 as a land holding company. The last incarnation of the Southern Pacific, the Southern Pacific Transportation Company, was founded in 1969 and took over the Southern Pacific system. The Southern Pacific Transportation Company was taken over by the Union Pacific Corporation and merged with their Union Pacific Railroad. The Southern Pacific Transportation Company was the surviving railroad as it absorbed the Union Pacific Railroad and changed its name to "Union Pacific Railroad", the Southern Pacific Transportation Company is now the current incarnation of the Union Pacific Railroad.

Freight Cars

Specific timeline unknown. 

1940: Known in use.  "SP" reporting marks.
1947: Known in use, at least for the T&NO:
1948: Known in use. "SOUTHERN PACIFIC" spelled out with line above. Herald on other side.
1955: Known in use.  "SOUTHERN PACIFIC" in large type opposite herald.
Correct for 1959: ACF Type 27 Riveted 10,000 Gallon Tank Car
1965: Known in use. No herald.
1972: Known in use (special purpose):
1974: Known in use (special purpose):