Miner Peabody Energy Corp , whose coal fuels 10 percent of America's electricity generation, said first-quarter profit tripled as higher-price contract sales offset slumping spot coal prices.

Net earnings were $170 million, or 63 cents per share, compared with $57 million, or 21 cents per share, in the same quarter of 2008, the St. Louis-based company reported on Wednesday.

Income from continuing operations was 50 cents per share. Revenue rose 15 percent to $1.46 billion.

During the first quarter, coal prices dropped dramatically. A ton of eastern U.S. coal that cost $61.50 on January 1 slumped 25 percent to $45.63 on March 31.

Analysts attributed Peabody's revenue increase to the fact that the company sold much of its coal production at locked-in contract prices negotiated before the recent drop in spot prices.

(Reporting by Steve James; editing by John Wallace)