BP (BP) is already tapping the trend. In July, it said that it would pay Chesapeake Energy (CHK) $1.75 billion for land in Oklahoma's Woodford Shale.

Smaller U.S. explorers also could be buyers. XTO Energy (XTO) has recently gobbled up roughly $5 billion in shale assets. In addition, investors in Asia and the Middle East are raring to buy U.S. shale assets for their strong rates of return, says Ray Perryman, president of the Perryman Group, a Waco, Texas, economic-research firm that advises small energy companies.

St. Mary could become a target of a large energy outfit, says Will Nasgovitz, whose Heartland Select Value Fund owns the stock. Applying recent transaction prices to St. Mary's existing assets, and assuming $80 crude (it's near $115 a barrel) and $8 natural-gas prices, he contends that the stock is worth 75, nearly twice its current price of 43. Nasgovitz estimates that St. Mary's acres in the Haynesville region, where Texas meets Arkansas and Louisiana, would bring $16 a share, based on recent purchases by Chesapeake and Plains Exploration and Production (PXP). Add another $12 a share for Woodford acres in Oklahoma and $12 for Bakken land in Montana, and you're at $40, but "these plays account for a fraction of their total production," says Nasgovitz. "The assets are worth more, if they sell."

Shares of Quicksilver (which also has a master limited partnership) have been hurt by the decline in natural-gas prices; they're now more than 40% below their 52-week high. While the shares are relatively pricey, with an enterprise value-to-Ebitda multiple of 12.7, analysts expect earnings to jump 41% in 2009, according to Thomson Reuters. Citing "phenomenal momentum in the Barnett," Jeffries & Co. recently bumped up its 12-month price target on Quicksilver to 56, versus a recent 26. The stock now trades near the proved value of its reserves, based on $75 oil and $8 natural gas. And recent acquisitions may help boost those reserves by 76%, Jeffries estimates.