Private equity firm Blackstone Group is in advanced preparations for a flotation.

Blackstone is believed to be working with investment bank Goldman Sachs on an IPO (initial public offering) prospectus for that could be filed in the next couple of weeks, although a final decision has not yet been made.

The filing would open up to public view the firm’s financial information, which has been closely guarded ever since financiers Steve Schwarzman and Pete Peterson set up Blackstone as a small Wall Street boutique in1985. It is thought the most likely structure for an IPO of Blackstone is an initial sale of about 10% of the firm.

The largest buy-out groups have considered the idea of going public for some time as a way of securing a permanent source of capital and allowing their ageing founders to cash in on the value of the firms they built. Peterson, who served as US commerce secretary in the Nixon administration, is 80, while Schwarzman recently turned 60.

A recent McKinsey study for the Financial Times estimated that Blackstone would be worth around $60bn (£30bn), if it were to go public, less than its US rivals Kohlberg Kravis Roberts and Carlyle.