A significant increase in the seaborne trade for coal over the past 20 years has unified formerly separate coal markets into a world market in which prices move in tandem. By virtue of its large domestic market, the USA has become the residual supplier and price setter in the world coal market. Changes in multifactor productivity have been the primary cause of the long-term fluctuations in coal prices that have been observed in the USA since the end of the Second World War and in the world coal market.