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 St. Louis-based company, one of the nation's biggest coal producers, 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 is the parent company of the Thunder Basin Coal Company, which operates in Wyoming.

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.

Company shares jumped 5 percent, or $2.53, to $53.47 at the open of trade.

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 Central Appalachia operations averaged $69.54, compared with $48.36 during last year's second quarter. The company's operating margin increased roughly six-fold, to $20.16 from $3.51.

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, handily 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.

Peabody said Wednesday that China has idled more than 60 coal plants because coal inventories have shrunk to less than three days supply. China also has trimmed its coal exports by more than 8 percent this year and announced plans to lower or eliminate its coal import tariffs, Peabody said.

Peabody also said India will need 78,000 megawatts of new coal-fueled generation by 2012, meaning an additional 265 million tons of coal use in that country.

"Given tight supply conditions and strong demand for coal globally, we have reached price levels that are unprecedented," said John Eaves, Arch's president and chief operating officer. "At the same time, we continue to believe these strong pricing levels are sustainable over the next several years."

Coal from Arch, which last year had revenues of $2.4 billion, fuels about 6 percent of all U.S. electrical generation.