The biggest allocation of USRA Light Mikado went to the Baltimore and Ohio Railroad, the first common carrier railroad and the oldest railroad in the United States.
The Baltimore and Ohio Railroad (reporting marks B&O, BO) was the first common carrier railroad and the oldest railroad in the United States, with its first section opening in 1830. Baltimore and Ohio Railroad 100 Western Pacific Railroad Wabash Railroad Union Pacific subsidiary Oregon Short Line Railroad Union Pacific Railroad 5 20 20 20 Texas and Pacific Railway Southern Railway St. Louis  San Francisco Railway (23 from PRR, 10 from IHB) 25 11 10 6 3 (30) 5 Pennsylvania Railroad subsidiary Grand Rapids and Indiana Railroad Pere Marquette Railway Pittsburgh and West Virginia Railway Rutland Railway Seaboard Air Line Railroad Pennsylvania Railroad New York, Chicago and St. Louis Railway ("Nickel Plate Road") New York Central subsidiary Toledo and Ohio Central Railroad New York Central subsidiary Michigan Central Railroad 20 15 10 (33) 15 24 25 New York Central subsidiary Cleveland, Cincinnati, Chicago and St. Louis Railway New York Central subsidiary Indiana Harbor Belt Railroad New York Central subsidiary Lake Erie and Western Railroad New York Central Railroad 95 10 Nashville, Chattanooga and St. Louis Railway Monongahela Railway Missouri Pacific Railroad Maine Central Railroad Louisville and Nashville Railroad 18 6 15 (+10 from PRR) 10 4 25 15 9 (+11 from T&P) Chicago, Rock Island and Pacific Railroad Grand Trunk Railway Grand Trunk Western Railroad Lehigh and Hudson River Railway Chicago, Indianapolis and Louisville Railroad ("Monon") Chicago Great Western Railway Chicago and Eastern Illinois Railroad Chicago and Alton Railroad 10 15 10 5 
