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KAI RYSSDAL: Today was one of those days the commodities market thumbed its nose at all the smart guy analysts. You might have heard the headline this morning that winter heating prices are expected to be lower this year. As much as $119. So, of course, natural gas prices rose today. Up 4 cents. Oil, though, fell through the floor. Off a $1.44 to its lowest level in eight months. It sounds all sexy in a business kind of way, but private equity is about to get some unwanted attention.

Three firms set a record for a private buyout this summer when they bought the hospital operator, HCA, for almost $33 billion. Earlier, another group bought the Spanish-language TV company Univision for almost $14 billion. But all that cooperation is raising some eyebrows at the Justice Department. It's launched an inquiry into possible anticompetitive behavior among some of the private equity world's most prominent players.

From New York, Ashley Milne-Tyte has that story.

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ASHLEY MILNE-TYTE: A private equity fund is a large pool of money usually gathered from institutional investors. The pool is used to buy a company, often privately held. The group then runs it and may take it public down the road. Pete Kyle teaches finance at the University of Maryland:

PETE KYLE: "There are a very large number of private equity firms, and they're all out there looking for deals, and the search for deals is one that involves cut-throat competition."

On the other hand the deals are increasingly so large, private equity firms have to band together to raise enough capital for a buyout. Laurence White of New York University says that may be what's caught the attention of the Justice Department. He says the worry is that the bidding process for a company might resemble an auction where buyers agree among themselves not to outbid one another, but to let the other guy get the first shot. He says in that case the owners of the company that's up for sale lose out.

LAURENCE WHITE: "The shareholders, if it's a publicly traded company, who would receive a lower price for their shares if there was some understanding among the private equity firms to not get into a competitive battle with each other."

The private-equity firms aren't talking about the probe. Nor is the Justice Department. But the investigation seems to be at an early stage, with requests for information being sent out. Some analysts say other probes have died out after this stage, and that this one will be no different.

In New York, I'm Ashley Milne-Tyte for Marketplace.