Coal could become the world's top source for energy in five years, according to the International Energy Agency. Compared to today, as much as 1.2 billion more tons of coal per year could be burned by 2017, which is the equivalent of the total coal consumption of Russia and the United States combined.

This means that the use of coal could come close to surpassing that of oil. The IEA estimated that global consumption for coal in 2017 will be 4.32 billion tons of oil equivalent (btoe), versus 4.4 btoe for oil.

Energy demand in China and India will drive most of the growth in coal, the report stated, with China surpassing the rest of the world in coal demand.

The only region of the world that demand for coal is not expected to increase is the United States. Instead, the U.S. natural gas market will take the lead over coal.

“The U.S. experience suggests that a more efficient gas market, marked by flexible pricing and fueled by indigenous unconventional resources that are produced sustainably, can reduce coal use, CO2 emissions and consumers’ electricity bills, without harming energy security,” said IEA Executive Director Maria van der Hoeven.

PennEnergy's research area offers details on coal energy usage.