Another type of cartel is the bidding ring.

When the secrecy surrounding the bidding ring was broken, a scandal was threatened.

Bidding rings can be both sophisticated and long-lasting.

Since the auctions are of the many-winner financial type, a knockout system, as in the stamp bidding ring, is unlikely.

Guy Sbar, a New Jersey doctor who uses the name "docharpo," also said he was not part of any bidding ring.

The sale was part of an agreement with E.ON when it pulled out of the Endesa bidding ring.

"The problem was not so much what the BBC paid, but what the BBC was doing in the bidding ring in the first place," the report said.

A fugitive accused of taking part in a fraudulent bidding ring on the eBay online auction service has been arrested in Wichita, Kan., and will be brought to trial in Sacramento.

For example, if one member of the bidding ring is designated to win a particular contract, that bidder's conspirators could avoid winning either by not bidding ("bid suppression"), or by submitting a high bid ("cover bidding").

According to the indictment, the bidding ring had eclectic tastes in art, selling and bidding on hundreds of paintings that seemed to have been created by artists like Edward Hopper, Alberto Giacometti and Clyfford Still.

However, the fraud was discovered, and after Walton was investigated, it was uncovered that Walton, Scott Beach, and Fetterman were involved in a shill bidding ring and that Fetterman had faked many paintings.

In a 1992 paper on bidding rings, Preston McAfee, now at Google, and John McMillan, then of the University of California, San Diego, outlined four challenges that bidding rings face.