NEW YORK (AP) — Blackstone Group LP, the investment firm known for making billion-dollar bets to buy huge companies and take them private, jumped almost 20 percent yesterday in its debut on the New York Stock Exchange.The New York-based buyout shop fluctuated wildly in the first few minutes of trading as investors scrambled to get a piece of the nation's second-largest private equity firm. After pricing at $31 late Thursday, the stock opened up $5.45, or 17.6 percent, at $36.45. It was trading at $36.90 just after 10:20 a.m. EDT.

An estimated 47.7 million shares exchanged hands in early trading, reflecting heavy demand from institutions and money managers to buy into the biggest private-equity firm yet to tap the public markets. The flotation at $31 valued Blackstone at about $33.6 billion, making it one of Wall Street's biggest players.

"There was heavy demand out there, especially because this came a week early, and it opened pretty much as expected," said Ryan Larson, senior equity trader at Voyageur Asset Management, a subsidiary of RBC Dain Rauscher. "I think with the demand that's out there that you'll see this trade up, and maybe sell off a bit in a week or so to a more normal range."

For Blackstone co-founder and chief executive Stephen Schwarzman, the stake of about 222.8 million common units that he reported in a regulatory filing Thursday was worth $8.22 billion at the most recent trade. That is on top of the hundreds of millions of dollars worth of units he was expected to sell in the offering.

There was some confusion about the initial price on Friday, with various data providers reporting first trades north of $40 a share, though those were not believed to be official opening quotes. A spokesman for the New York Stock Exchange was not immediately available to comment.

The offering is the biggest US IPO in five years, and could open the floodgates for other alternative investment funds to go public. There were reports that rival Kohlberg Kravis Roberts & Co. hired its own bankers to pursue an IPO, and that Carlyle Group is also mulling a public offering.

So far, exuberance about the booming private-equity industry has been able to overshadow mounting criticism about the lavish lifestyles of top executives on Capitol Hill, among labour unions, and in the media.

For those lucky enough to get in on the IPO, the biggest appeal is that it gave investors a chance to participate in the private equity industry, where firms buy companies, turn them around, and seek to sell them at a profit.

And investor appetite was strong to buy a part of Blackstone, even though the stake in its management business has little voting power or any direct connection to its portfolio of companies.

It also came amid a growing fight by lawmakers to stop the deal. The New York-based buyout shop acknowledged Thursday it could face much higher taxes as early as next year if it is taxed as a corporation instead of as a partnership, as a new bill in the US House of Representatives proposes to do.

The proposal would effectively bring Blackstone's tax rate to as much as 35 percent, from 15 percent now. That came on top of a previous warning from Blackstone that compensation and other costs related to going public would cause it to not be profitable for years.