Surface mining is a very efficient and low cost way to mine coal. This is especially true in the West where the coal seams are very thick (those in the Powder River Basin of Wyoming average 100 feet). In 1997, mine mouth coal prices for Wyoming's Powder River Basin coal was $5.40 per ton. In Chicago, Powder River Basin coal sold for $60.00 per ton in 1997. Hannah Basin (Southern Wyoming) mine mouth coal sold for $17.10 per ton. The difference was in the higher BTU level, the lower moisture, and the lower ash content of Hanna coal.