) -- Newly minted shares of

Cobalt International Energy


tumbled in their debut on the

New York Stock Exchange

after the company's stock was priced below expectations.

Cobalt offered 63 million shares at $13.50 each, less than the $15 to $17 it had predicted. The deal raised $850.5 million, which could reach $978.1 million if underwriters exercise an option to purchase 9.45 million additional shares.

Shares of Cobalt fell by as much as 7% after the pricing, and are currently changing hands at $13.41.

The past week has been the most volatile for initial public offerings this year, according to


(MORN) - Get Report

. Only four of the eight deals scheduled to hit the market have managed to price.

"We have been asked many times over the past few weeks what to make of the growing trend of failed deals," Bill Buhr, head of Morningstar's IPO research team, wrote in a note Wednesday. "We think it's part of a normally functioning IPO market, especially now that more companies are trying to raise funds."

Unsurprisingly, the first half of 2009 was slow for IPOs, with only 14 coming to market. The companies that did go public possessed "strong fundamentals in recession-resilient sectors," Buhr wrote. As a result, they were some of the

best performing new issues of 2009


"Now that the door has been thrown wide open, with firms all along the quality spectrum trying to raise funds, it should not surprise anyone that investor demand for some of these offerings would be weak to non-existant," Buhr wrote.

In fact, of the 10

worst IPOs of 2009

, as measured by stock-price returns, eight came to market in the second half of the year.

Though there were several successful REIT IPOs earlier in the year from

Cypress Sharpridge Investments



Starwood Property Trust

(STWD) - Get Report

, "by the time September rolled around, the add-on REIT IPOs were harder to distinguish from each other, and ultimately experienced tepid demand," Buhr wrote.

Last week,

Chesapeake Lodging Trust


Ellington Financial

failed to price.

Pebblebrook Hotel Trust

(PEB) - Get Report

, a hotel REIT, managed to raise $350 million.


(KAR) - Get Report

, a used-vehicle auctioneer, offered 25 million shares at $12 apiece, significantly below the expected range of $15 to $17 a share.

Also on deck this week:

National Beef


Team Health


Kraton Performance Polymers

, none of which Buhr is overly excited about, he said.

--Reported by Jeanine Poggi in New York.


>>Worst IPOs of 2009: Biggest Stock Flops

>>Top IPOs of 2009: Five Stocks to Watch

>>Which OPO Will Be Most Successful?

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