Shares of Fortress Investment Group LLC (FIG) opened up 89 percent in a highly anticipated market debut on Friday, the first by a diversified private equity and hedge fund in the United States.

Shares of the company opened at $35, before slipping to $31 or up 68 percent in morning trading on the New York Stock Exchange.

Click here to visit FOXBusiness.com's Investing page.

On Thursday, the 34.3 million class A share offering sold for $18.50 each compared with a $16.50 to $18.50 forecast range, raising $634 million.

The offering price gave the New York-based company an initial market capitalization of more than $7.4 billion.

Shares of the U.K.'s Man Group (EMG.L), the world's largest listed hedge fund company with more than $60 billion under management, have more than doubled over the past two years.

Fortress has ballooned from its inception in 1998, growing assets to $29.7 billion at the end of September 2006 from $1.2 billion at the end of 2001.

Net income rose to $192.7 million in 2005 from $40.3 million in 2003.

Due in part to its financial performance, the company packed rooms for its road show presentations which led to shares being "massively" oversubscribed, said Scott Sweet, managing director for IPO research firm IPOboutique.com.

"Road shows were wall to wall and standing room only," Sweet said.

The offering represents 8.5 percent of total shares in the company, but principals of the firm — Peter Briger, Wesley Edens, Robert Kauffman, Randal Nardone and Michael Novogratz — own 100 percent of the class B shares and about 78 percent of shareholder voting power, according to a filing with the U.S. Securities and Exchange Commission.

Fortress went public to "maintain and expand our position" in the global investing arena, reward talented employees, give it acquisition currency and give it a sense of "permanence" with investors, the company said in the filing.

The firm, which calls itself one of the largest 'alternative' investment managers, plans to use net proceeds from the offering to repay debt and for general business purposes.

Underwriters, led by Goldman Sachs and Lehman Brothers, Banc of America Securities LLC, Citigroup, and Deutsche Bank Securities, have the option to buy an additional 5.1 million Class A shares to cover overallotments.

Click here to visit FOXBusiness.com's Investing page.