According to the Associated Press, PRB coal on a one-month contract basis has risen 67% to $US13.80 per ton compared with last October.

In fact, Platte River Power Authority production manager Jason Frisbie, whose agency serves more than 1.6 million customers in areas of Colorado, said PRB coal was previously $5/t.

The price began to rise as the coal began being shipped east.

"The next wave came as more coal began moving overseas," he told the Denver Post over the weekend.

Colorado Springs Utilities fuel manager Michele Fujimoto, whose firm also serves Colorado, told the newspaper that long-term contracts and hedging were keeping a damper on the impact of the rising price.

"We are expecting the market price to climb," she said.

"Over the past five years, coal market prices have seen peaks, valleys and a general escalation in delivered prices,” Wood MacKenzie coal analyst Francis Roberts reportedly told the newspaper.

“This sort of price volatility is typical of today's coal markets and reflects the fact that coal markets are now more globally interconnected."

In total, according to the 2010 BP Statistical Energy Review, the US holds 260 billion short tons of coal reserves, 29% of the world’s reserve position.

At current levels, the PRB has a 150-year coal supply for the nation.