ST. LOUIS — Arch Coal Inc. said Friday its second-quarter profit tripled on soaring global prices and tighter coal supplies, easily beating Wall Street expectations.

The performance, on the heels of similar big numbers Wednesday from coal-mining counterpart Peabody Energy Corp., sent Arch's shares climbing more than 9 percent, or $4.70, to close at $55.64 Friday.

The St. Louis-based company, Utah's largest coal producer, raised its earnings forecast for 2008, citing what Arch's top executive called "our confidence in coal-market fundamentals and in the company's future growth prospects."

Arch reported net income of $113 million, or 78 cents per share in the latest April-through-June period. That compared with $37.6 million, or 26 cents per share, during the same period last year, in which Arch's profit dove 46 percent after it reined in production amid a softer market.

Revenue rose to $785.1 million, from $598.7 million in last year's second quarter, propelled by higher sales prices in every one of its operating regions.

Analysts surveyed by Thomson Financial expected earnings per share of 64 cents and revenue of $737.1 million.

Arch said it now expects profits of $2.50 to $2.85 per share. Just three months ago, the company predicted it would earn $2.40 to $2.80 per share, up from its previous prediction of $2 to $2.50 per share.

"We are on track to deliver our best earnings performance in company history during 2008," Steven Leer, Arch's chairman and chief executive, said in a statement.

The company sold 34.4 million tons of coal during the quarter, compared with 33.3 million tons during the same period last year. Each ton Arch sold fetched on average $21.04, up from $16.42 a year ago and $18.49 over this year's first three months. The company's operating margin per ton averaged $4.21, more than double the $1.75 average a year ago.

Sales of coal from Arch's Utah operations totaled 13 million in 2007, more than half of the state's production, said Michael Vanden Berg of the Utah Geological Survey. The company owns the Dugout, Skyline and SUFCO mines.

Over the first half of this year, Arch said it earned $194.1 million, or $1.34 per share, on revenues of $1.48 billion, compared with $66.3 million, or 46 cents per share, on $1.17 billion in revenues during the same period last year.

Arch's latest numbers offered more evidence of the coal sector's strength. On Wednesday, St. Louis-based Peabody Energy Corp. reported second-quarter profits that more than doubled to $233.4 million, or 86 cents per share, beating Wall Street's expectations. Peabody said its revenue rose 43 percent to $1.53 billion.

Combined with high ocean shipping rates and the weak dollar, strong demand for coal has helped fuel a resurgence in U.S. coal exports.The global thirst for coal has been robust in countries such as China and India.