A Class I railroad in the United States and Mexico, or a Class I rail carrier in Canada, is a large freight railroad company, as classified based on operating revenue.
Smaller railroads are classified as Class II and Class III. The exact revenues required to be in each class have varied over time, and they are now continuously adjusted for inflation.
The Surface Transportation Board (STB) defines a Class I railroad in the United States as "having annual carrier operating revenues of $250 million or more" after adjusting for inflation using a Railroad Freight Price Index developed by the Bureau of Labor Statistics (BLS). According to the Association of American Railroads (AAR), Class I railroads had minimum carrier operating revenues of $346.8 million (USD) in 2006, $359 million (USD) in 2007, $401.4 million (USD) in 2008 and $378.8 million (USD) in 2009.
In Canada a Class I rail carrier is defined (as of 2004) as a company that has earned gross revenues exceeding $250 million (CAD) for each of the previous two years.