HARRISBURG — A leading exploration firm on the largely untapped Marcellus Shale natural gas formation said it almost quadrupled its gas flow from a year ago.

Range Resources said today it is producing 1 million cubic feet of natural gas each day from its wells in southwestern Pennsylvania.

That's enough natural gas for about 500,000 homes every day. The Fort Worth, Texas-based firm said it expects to double that flow next year.

Company spokesman Matt Pitzarella said Range has paid out more than $20 million in landowner royalties on its Marcellus Shale wells.

Geologists say the Appalachian gas field could become the nation's most prolific. By some estimates, it holds enough natural gas to supply the United States for up to two decades.