Anadarko Petroleum Corp.'s blockbuster $21 billion move on Friday to buy two sizeable U.S. oil and gas companies signals that a rush is on to grab energy assets, even with their lofty price tags.

With energy companies facing growing cash hoards and few places to plow the money, analysts predict that buying in the sizzling sector will only accelerate.

With the sector swimming in cash and growth opportunities limited, we expect more deals, UBS analysts said in a research note on Friday.

With few willing to bet that oil and gas prices will decline significantly any time soon, companies seem unconcerned about paying top dollar for assets.

And, analysts say, a shrinking pool of smaller U.S. exploration and production companies, such as Ultra Petroleum Corp., Newfield Exploration Co. and Quicksilver Resources Inc. in particular, could prove to be attractive targets.

When the boards of all these small companies meet now, they're going to have to decide whether they want to be among the hunters or the hunted, said Charles Maxwell, an analyst at Weedon & Co. If you make no decision, then you're among the hunted.

Anadarko became the latest to join the acquisition fray by unveiling deals to acquire smaller rivals Kerr-McGee Corp. and Western Gas Resources Inc. for $21.1 billion in total, boosting its presence in the U.S. Gulf of Mexico and the Rocky Mountains region.

Reflecting its bullish outlook for the sector, Anadarko forked out a 40 percent premium to Kerr-McGee's pre-announcement share price, while Western Gas commanded a 49 percent premium.

Those purchases follow a stream of acquisitions in the U.S. energy sector in the past year. Many have been smaller, like Energy Partners Ltd.'s deal to buy Stone Energy for $1.4 billion earlier on Friday and Devon Energy Corp.'s $2 billion deal to buy Chief Holdings LLC.

But there have been a few mammoth deals, such as No. 3 U.S. oil company ConocoPhillips' $34 billion acquisition of Burlington Resources Inc. and Chevron Corp.'s purchase of Unocal Corp. last summer.

PRICEY AND PRICIER

Expensive price tags in all of those deals did not deter oil companies, which find themselves with an increasingly smaller pool of growth options.

Most of the energy-rich regions of the world like the Middle East and Russia are increasingly off-limits to Western companies, and easy discoveries in traditional exploration hotspots like the Gulf of Mexico are a thing of the past.

Anadarko's deal highlights the potential of the Rockies, and it could help boost the shares of companies such as Ultra, Newfield, and Quicksilver, as well as EOG Resources Inc. and Devon Energy Corp., UBS analysts said.

Energy companies are generating record profit, and they have dwindling access to resources, said Fadel Gheit, analyst with Oppenheimer &Co.

They could acquire overseas, but many countries are closing doors and windows to their resources for foreigners. So the U.S. is the only logical place they can expand.

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(Additional reporting by Joseph Giannone and Dan Wilchins in New York)

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