(Bloomberg News) More than half of the U.S. initial public offerings planned for this year are from private equity firms as KKR & Co., Blackstone Group LP and Carlyle Group try to unload some of their biggest leveraged buyouts.

HCA Holdings Inc., Nielsen Holdings BV, Kinder Morgan Inc. and more than two dozen other companies owned by private equity firms have asked the Securities and Exchange Commission for permission to sell $14 billion of shares in IPOs, or 53% of the amount on file, according to data compiled by Bloomberg. The total is more than double the $6.6 billion raised in 2010, when their initial offerings accounted for 15% of sales.

Buyout firms are betting that a rebound in equity values will increase demand for some of the debt-fueled acquisitions completed as credit markets started to freeze four years ago. While the Standard & Poor's 500 Index has recovered all its losses since the collapse of Lehman Brothers Holdings Inc. in 2008, the funds are now seeking buyers for companies with almost twice the net debt to operating cash flow as the average private equity-backed IPO last year, data compiled by Bloomberg show.

"Private equity is certainly going to continue to bring to market either to monetize or de-lever the companies they bought," said Robert H. McCooey Jr., senior vice president of new listings and capital markets at Nasdaq OMX Group Inc. in New York. "That will be a big piece of the IPO market."

Equity Market Rebound

Share sales accelerated last quarter as the S&P 500 climbed to the highest level in more than two years on speculation companies will become more profitable as the U.S. economy recovers from the worst recession in more than 70 years. Almost 40% of the IPOs last year were completed after the start of October, data compiled by Bloomberg show.

While private equity firms were behind 31 initial sales in the U.S. last year, shares of the companies left buyers with the smallest gains. They rose 3.8% on average in the first month of trading, less than half the 8.1% advance for all other IPOs, data compiled by Bloomberg show. Venture capital- backed offerings, which raised $3.2 billion, increased 7.8% on average.

More than 120 companies are seeking approval from the SEC to raise about $26 billion through IPOs, the data show. Barclays Plc of London estimates that U.S. companies will complete as much as $50 billion of sales this year, a 34% increase from 2010.

'Big Window'

"The pipeline should be an indication of what's coming over the next six to 12 months," said Paul Bard, director of research at Renaissance Capital LLC, the Greenwich, Connecticut- based IPO research and investment firm. "We wouldn't be surprised to see both the number and the proceeds increase, so you could potentially see the amount of money raised double."

In LBOs, private equity firms borrow most of the money used to take controlling stakes in companies. They try to increase the value of those companies by cutting costs, eliminating workers and closing unprofitable businesses, with the aim of unloading their stakes at a higher price.

A record $1.6 trillion in LBOs were completed from 2005 to 2007, according to Preqin Ltd., a London-based research firm.

"We had a big private equity boom a few years ago with easy credit and lots of it, and then we had sort of a nasty recession where private equity investors couldn't get an exit," said Timothy Cunningham, a manager at Santa Fe, New Mexico-based Thornburg Investment Management, which oversees about $70 billion. "This is the first big window where we can see an exit. Private equity funds will try to take advantage of that."

HCA Borrowings

HCA, the hospital chain bought four years ago for $33 billion in what was the world's biggest LBO, is planning a $4.6 billion IPO, according to its prospectus.

At the time, funds led by New York-based KKR and Bain Capital LLC of Boston put up about $5.3 billion and borrowed the rest. The Nashville, Tennessee-based company plans to use the proceeds from the IPO to pay debt, which exceeded its cash by $25.7 billion at the end of September.

HCA also borrowed about $1.53 billion in November to fund a cash payout to its private equity owners, meaning that KKR and Bain are selling stakes in a company that would need five years' worth of the earnings before interest, taxes, depreciation and amortization it generated last year to pay off all the debt, according to data compiled by Bloomberg.

More than $14 billion of HCA's borrowings are due within three years, according to the company's SEC filing. In 2010, private equity-backed IPOs had average net debt of about 3.65 times annual Ebitda, the data show.

Debt Burden

"Leverage is always a concern," said Lawrence Creatura, a Rochester, New York-based fund manager at Federated Investors Inc., which oversees $29 billion of equities. "You'll have to endure the burden that most free cash flow is going towards debt service and debt pay down."

Nielsen, the New York-based television-audience rating company taken private by six firms including KKR, Blackstone and Carlyle in 2006, and Kinder Morgan, the Houston-based pipeline company acquired in a $22 billion LBO a year later, are more indebted than HCA.

Nielsen, which had a net debt-to-Ebitda ratio of 6.5, filed to raise as much as $1.73 billion in an initial offering to repay creditors, according to data compiled by Bloomberg.

Carlyle, Goldman Sachs

Kinder Morgan, owned by a group that includes Washington- based Carlyle and Goldman Sachs Group Inc. in New York, has 7.2 times more net borrowings than its Ebitda over a full year, about the average for private equity-backed companies that have IPOs pending SEC approval, the data show. The pipeline company's owners plan to unload $1.5 billion of shares in the sale.

Kristi Huller, a spokeswoman for KKR, declined to comment, as did Blackstone's Peter Rose and Christopher Ullman at Carlyle. Michael Duvally, a spokesman for Goldman Sachs, and Bain's Alex Stanton also declined to comment.

HCA, Nielsen and Kinder Morgan were among the world's 20 largest-ever leveraged buyouts, according to Preqin. The last LBO of that size to attempt an IPO was Las Vegas-based Harrah's Entertainment Inc., which terminated a $531 million sale in November after failing to attract enough buyers.

Apollo Global Management LLC of New York and Fort Worth, Texas-based TPG Capital took Harrah's private for $30.7 billion, including debt and transaction costs, in January 2008.

Venture Capital

Companies controlled by buyout firms face more pressure to go public to pay back the debt from their LBOs, while their owners want to cash out as soon as possible, said Tim Loughran, a finance professor at the University of Notre Dame's Mendoza College of Business in Notre Dame, Indiana.

Venture capital-backed companies have filed to raise $2.86 billion in IPOs, a decrease from last year's total and 79% less than private equity-owned companies.

While companies such as Facebook Inc. and Twitter Inc. have increased in value by 50% or more in private trading on speculation they will go public, venture-backed companies have shown they can raise equity capital without seeking an IPO. Facebook raised $500 million from Goldman Sachs and Russia's Digital Sky Technologies, the New York Times reported yesterday, citing unidentified people involved in the transaction.

Groupon Inc., the daily-deal coupon site based in Chicago, raised $500 million in its latest round of financing, according to its SEC filing last week. The sale is more than half the $950 million that the company filed to raise on December 17.

Founded in November 2008, Groupon walked away from a $6 billion takeover offer from Google Inc. last month. The new funding lessens the pressure to seek an IPO this year, said Greg Sterling, an analyst at Internet2Go, an advisory service that is part of Opus Research in San Francisco.

The company topped $500 million in sales in 2010, people familiar with the matter have said, reaching the milestone faster than Amazon.com Inc., EBay Inc. and Yahoo! Inc.

"Facebook and companies like that can already sell equity without doing an IPO," said Loughran. "They can wait for a really good time to go public. The private equity firms have a lot of debt which forces their hand to move at a quicker pace."