The Wall Street Journal reports the famed auction house is preparing to sell six Nike Air Jordans that Michael Jordan wore during the six NBA championship games won by the Bulls in the 1990s. It’s a collection so rare (and so coveted by the sneakerhead collective) that even Sotheby’s won’t hazard a guess as to what it will fetch.

One collector told the Journal, though, that he estimates the minimum bid will be $20 million and the collection could fetch as much as $100 million. It’s expected to be the most expensive shoe collection ever sold, regardless of the amount.

The six shoes (shoes…not pairs) were initially collected by Tim Hallam, who got them from Jordan right after the final buzzer in the championship games. Hallam, a Bulls employee, no longer owns the shoes, and it’s unclear who does.

“I don’t play; I don’t score; I don’t rebound, so the [championship] rings don’t mean quite as much to me as they do the players,” Hallam told the Journal. “I wanted something that was an actual part of the game, so I asked Michael for one of his shoes.”

The auction comes amidst something of a perfect storm. Sneakerheads have been driving up the price of rare shoes for some time. The sports memorabilia market is red-hot these days. And the success of documentary The Last Dance has sparked a revival of interest in Jordan items. Last year, a jersey Jordan wore during the 1998 NBA finals sold for a record $10.1 million.