Thomas Hicks did it. Nelson Peltz is doing it. And on Friday, Ronald O. Perelman, the billionaire financier whose firm owns Revlon, joined the parade.

We are talking about Spacs, or special-purpose acquisition companies, whose sole purpose in life is to make a deal. The popularity of these vehicles, also known as blank-check companies, has exploded this year, and it seems as if every deal-maker needs to have one.

While each Spac is relatively small — at least in the jaded world of Wall Street, where real money is measured in billions — when taken together, they represent a big slug of cash trawling for takeover targets.

So far in 2007, I.P.O.’s of Spacs and blank-check companies in the United States have raised a total of $11.3 billion, according to Dealogic. The latest Spac to go public, Liberty Acquisition, is also the largest: It raised $900 million in an initial public offering that priced late Thursday.

There’s more to come: There are 29 Spacs in the I.P.O. pipeline seeking to raise an additional $6.7 billion. And that figure doesn’t include MSAF Acquisition, Mr. Perelman’s blank-check company, which filed with regulators early Friday to raise $500 million.

What’s the appeal of a Spac? For the Spac itself, it provides a relatively easy way to raise funds for an acquisition. Relying on little more than the reputations of its founders, a Spac can pull together hundreds of millions of dollars in a few months.

Mr. Hicks, a veteran of the leveraged buyout industry who owns the Texas Rangers, raised $550 million for his blank-check company, Hicks Acquisition, in October, less than four months after it first filed to go public. Heckmann, whose directors include Former Vice President Dan Quayle, raised $400 million in about five months.

Mr. Peltz, whose firm, Triarc, bought and sold Snapple at a huge profit several years ago, has also created a Spac. It is called Trian Acquisition I, and an analyst at Lehman Brothers recently speculated it might try to buy some assets from food conglomerate Kraft.

Spacs can also be highly profitable for management. They are usually structured so that founders get a big stake in the company for a tiny fraction of what public shareholders pay.

And for a takeover target, a Spac provides a back-door way to go public, which could be attractive in volatile equity markets.

There’s a distinct downside as well, however. A Spac operates under a tight deadline, usually 24 months or so, in which it must complete a deal or else liquidate.

This has proven to be a challenge for Endeavor Acquisition, which is racing to complete its acquisition of American Apparel before the drop-dead date of Dec. 15. In a proxy statement sent to shareholders late last month, Endeavor cited “growing time constraints” as one of the reasons it agreed to raise the price it is paying for the company.

Endeavor’s deal may well get done, but there’s a potential cautionary tale. By their nature, Spacs have a gun to their heads, and that doesn’t help when you are at the negotiating table.