In the past year, Reliance Industries, Exxon Mobil and BG Group Plc have been among those spending heavily in the mainly natural gas-rich shales of Marcellus and Haynesville, and in Eagle Ford, rich in higher priced natural gas liquids.
However, year-to-date average gas prices have dropped by close to a third, while crude oil CLc1 is up about 12 percent.
Now, interest may be switching to oil, and Bakken looks well placed.
"The gas business is basically a bust," Plains Exploration and Production Co CEO James Flores said on a recent conference call with analysts.
Among the unconventional shales, or tight rock formations, Bakken has the highest crude oil content, prompting analysts and industry experts to predict an M&A windfall for the region that straddles North Dakota, Montana and Saskatchewan.
"The large U.S independents like Devon Energy and Anadarko are increasingly coming to the view that some exposure to oil is good," Frank Murphy, an investment banker with Robert W Baird, told Reuters.
Murphy said these companies were underexposed in the oil shales, so there was potential for them to move in either through joint ventures or buying companies active in the Bakken.
In late July, Hess Corp said it was buying small-cap Bakken operator American Oil and Gas Inc for about $445 million. [ID:nLDE66R02B] Other big independents already in Bakken include EOG Resources and Marathon Oil.