Currently, there is not enough production capacity for coal supplies to meet demand, meaning that prices will stay high (better profit margins) until demand is met. This could take a while, and, given the economy's expansion, full demand may not even have been reached yet, meaning that there are years of high revenues and prices ahead.
As the world economy expands, there is an increasing demand for electricity, and coal is the cheapest source of power. As the largest private-sector coal firm, Peabody is in a great position to take advantage of this.