Industry experts say in the last three years companies like Anadarko Petroleum, Chesapeake Energy and Cabot Oil and Gas have leased up to two million acres for drilling in the region, half of that in the last nine months.

Whether their bets will pay off is by no means a sure thing.

Researchers at Penn State and the State University of New York at Fredonia estimate that the Marcellus has 50 trillion cubic feet of recoverable natural gas, roughly twice the amount of natural gas consumed in the United States last year. But government estimates of the amount of gas recoverable from the Marcellus are relatively modest.

Early test results have encouraged companies to keep drilling, but most are holding details of their test wells close to the vest.

The company that has done the most work is Range Resources of Fort Worth, which says it plans to invest at least $426 million in the Appalachia region this year.

The company has reported promising results from the first 12 wells that it has drilled horizontally, the technique considered by most experts to be the most effective in the Marcellus. The most recent six have each produced more than three million cubic feet of production a day in recent months, and company executives say that is better than the average for wells recovering natural gas in the Barnett Shale in north Texas.

“The Marcellus is important to Range and it could be important to the country but it really is still early,” said Rodney L. Waller, a senior vice president at Range. “I can build you a scenario where it can be significantly better than the Barnett but it’s a function of economics.”

Image Raymond Gregoire and his family outside their home near Williamsport, Pa. He recently signed a leasing contract. Credit... Kalim A. Bhatti for The New York Times

Energy experts say the Marcellus, along with other smaller shale formations being developed around the country, is coming under scrutiny at an opportune moment, just when conventional domestic natural gas production and imports from Canada are diminishing. With easy-to-find gas fields in decline, the country will need to explore in deeper waters in the Gulf of Mexico and penetrate deeper under the surface on land.