Blackstone, the US buyout firm, is working with no fewer than 17 underwriters on its flotation, including Goldman Sachs and JPMorgan Chase, it emerged yesterday, as the launch date for the IPO was set for June 25.

The float will raise about $4.5 billion (£2.2 billion) and value the management company at close to $33 billion. Wall Street firms have been scrambling to get a piece of the action. Morgan Stanley, Citigroup, Merrill Lynch, Credit Suisse and Lehman Brothers are among the host of other Wall Street firms underwriting the flotation.

Analysts believe that Blackstone has signed up more underwriters than necessary because it wants to keep as much of Wall Street onside as possible. Buyout firms such as Blackstone work closely with investment banks, which advise on deals and arrange financing.

The move will also reduce the potential for criticism of its valuation, which will see its shares trading on a much higher multiple than, for example, Goldman Sachs. Deutsche Bank, ABN Amro, Bank of America Securities, Nikko and Wells Fargo are also underwriting the offering, which is expected to value the shares at between $29 and $31 each.

Blackstone’s advisory army dwarfs the ten underwriters involved in the recent IPO of Fortress, the US hedge fund.

The underwriting arrangements emerged two days after the sheer scale of riches due to Blackstone’s two founders became known. Stephen Schwarz-man, the Blackstone chief executive and co-founder, will see his stake valued at more than $8 billion. He will cash in about $450 million of shares in the listing and retain a 23 per cent holding in the group.

Peter Peterson, a former chief executive of Lehman Brothers, will cash in $1.88 billion of his shares, leaving Blackstone’s other co-founder with about 4 per cent of the group.

Mr Schwarzman’s windfall comes after a year in which he earned $398.3 million, mostly from profits made on sales of portfolio companies. His 2006 earnings equate to 48 times the $8.3 million average total compensation paid to S&P 500 chief executives last year, according to Associated Press.

Even Lloyd Blankfein, chief executive of Goldman Sachs, earned only $54.3 million in 2006, a record for the head of a Wall Street firm, after his bank made unprecedented profits.

Blackstone will be the first US buyout firm to float, and so every new SEC filing is scrutinised as financial communities across the world seek an insight into a hugely secretive firm working in a notoriously opaque industry. Before Blackstone decided to go public, even its investors knew little about the firm, which, like most buyout groups, used its status as a private company to limit the flow of information.

But in recent weeks, Blackstone’s SEC filings have revealed nuggets of information, such as that the firm reported a net income of $2.26 billion for 2006, up from $1.3 billion in 2005.

In a reminder of just how cyclical an industry private equity can be, the company reported only $39.4 million for 2002, the filings have shown.

Rival buyout firms such as Kohlberg Kravis Roberts, Carlyle Group and Apollo Managers are among a host of Blackstone’s rivals that are watching the flotation with great interest, with a view to following suit.

There is expected to be a scramble to float if Blackstone’s IPO is a success, as experts predict that institutional investors would have an appetite for only two more buyout firms.

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