North American trains primarily use diesel fuel as their source of energy.. Electric locomotives are in widespread use in Europe and Asia and in some commuter runs in the United States.
Most diesel locomotives actually use a diesel-electric method of propulsion, which means that the diesel engine powers a generator that then produces the electricity used to run the train. Diesel fuel is one of the reasons that train travel is more energy efficient and more economical than air travel. Diesel fuel is produced at a higher volume per barrel of crude oil than jet fuel.
As the energy sector continues to change and global pressure grows for more energy efficient modes of transportation along with fewer carbon emissions, the global rail industry is working to develop other modes of power generation.