A more efficient and safer underground mining method, called longwall mining, uses a specially shielded machine which allows a mined-out area to collapse in a controlled manner. After coal comes out of the ground, it typically goes on a conveyor belt to a preparation plant that is located at the mining site. Removing the impurities increases the heating value of coal. After the coal is mined and processed, it is ready to go to market. Transportation is a very important consideration in coal's competitiveness with other fuels because sometimes transporting the coal can cost more than mining it.
Underground pipelines can easily move petroleum and natural gas to market.
But that's not so for coal. It is cheaper to transport coal on river barges, but this option isn't always available. Coal can also be moved by trucks and conveyors if the coal mine Is close by. Ideally, coal-fired electric power plants are built near coal mines to minimize transportation costs. When scientists estimate how much coal, petroleum, natural gas, or other energy sources there are in the United States, they use the term reserves.