The price of coal has exploded this year as worldwide demand has surged, but mining operations in the United States are struggling to keep up.

The price of central Appalachia coal averaged $73.25 per short ton, according to the U.S. Energy Information Administration’s most recent report. That is an increase of $2.20 from the week before, $7.45 from a month ago, and a 35% increase from earlier this year. Likewise, Australia’s Newcastle thermal coal, a global benchmark, is trading three times higher than at the end of 2019 at more than $200 per metric ton.