They are the reservoir formations of natural gas fields that have produced all their economically recoverable gas.

But Mr. Brand said the drilling demonstrated that substanital reserves of "recoverable gas remained in the Sabine Lake field."

Not only can gas and oil be extracted from fracking, but so can 500 million barrels of recoverable natural gas.

LEAD: The nation has a 35-year supply of recoverable natural gas at prices below $3 per thousand cubic feet, the Energy Department said today.

According to several recent analyses, Dr. Nakicenovic said, recoverable natural gas now appears far more abundant than had been previously thought.

It contains vast quantities of recoverable natural gas.

The volume of the gas in place and recoverable gas in this field is estimated at 13 and 9 TCF, respectively .

By comparison, the North Field off Qatar's coast is believed to hold 350 trillion metric tons of recoverable gas, none of it associated with oil deposits.

Recent shale gas discoveries have caused a sharp increase in estimated recoverable natural gas in Canada.

As of 2008, an estimated 5.2 trillion cubic feet of recoverable gas remains recoverable.