Italy's Eni SpA (E) is the latest European energy giant to buy into prolific shale-rock natural gas fields in the U.S., entering an alliance with independent producer Quicksilver Resources Inc. (KWK) to develop acreage in Texas.

Quicksilver will get $280 million by selling to Eni 27.5% of its Alliance properties in the Fort Worth Basin, which produce about 60 million cubic feet of natural gas a day. The companies are also joining forces to buy and develop about 270,000 acres surrounding Alliance.

The assets will give Eni a position in the Barnett Shale - a big gas field in North Texas credited for a sizable portion of the recent boom in domestic U.S. gas production. The deal will help the highly leveraged Quicksilver pay down debt and sent the company's share price up as much as 20% Monday.

Eni is the third European oil and gas company to buy into U.S. shale fields - tight rock formations that recent technological advances made economical to develop. Last year Chesapeake Energy Corp. (CHK) entered into joint ventures with BP PLC (BP) in the Oklahoma's Woodford Shale and with Norway's StatoilHydro ASA (STO) in Appalachia's Marcellus Shale.

"Big guys clearly want to understand (the) secret sauce around shale gas development," analysts with Houston-based Tudor Pickering Holt & Co. Securities Inc. wrote in a note to clients Monday, adding more of these transactions are likely to come.

Quicksilver shares were recently up 16% at $9.92 apiece. The stock has fallen roughly 75% in the past year amid a plunge in energy commodity prices and debt concerns. The company posted a first-quarter loss on write-downs of the value of its oil-and-gas properties, suspended its dividend and cut capital spending.

Quicksilver acquired the Alliance properties - which include natural gas production, acreage and midstream assets - last July from various private oil and gas companies for $1.3 billion. The deal with Eni does not include an interest in the midstream assets.

Many energy companies have run into trouble in recent months as the credit crunch ended their debt-fueled expansions and plunging prices have now made projects less economical. The troubles have prompted companies to shed assets, cut spending and idle rigs to shore up cash. Natural gas prices have fallen about 70% since July, when prices peaked above $13 a million British thermal units.

David Kistler, an analyst with Simmons & Co. in Houston, said the broad pullback in commodity and equity markets have spurred more interest from major energy companies in shale-gas production.

"It makes for an interesting time for companies to get a foothold in these shales," Kistler said.

Quicksilver President and Chief Executive Glenn Darden said in a press release that the deal represents 5% of its total proved reserves at the end of last year. The agreement is expected to close June 15.

-By Jason Womack, Dow Jones Newswires; 713-547-9201; jason.womack@dowjones.com

(Tess Stynes contributed to this report.)