The Missouri Pacific Railroad, commonly abbreviated as MoPac, was one of the first railroads in the United States west of the Mississippi River. MoPac was a Class I railroad growing from dozens of predecessors and mergers. In 1967, the railroad operated 9,041 miles of road and 13,318 miles of track, not including DK&S, NO&LC, T&P, and its subsidiaries C&EI and Missouri-Illinois.

The Texas and Pacific Railway Company was created by federal charter in 1871 with the purpose of building a southern transcontinental railroad between Marshall, Texas, and San Diego, California.