In what seems to be a quote from a financial disclosure document, Street Insider reports that Sotheby’s has guaranteed three works for the November sales with a total guarantee of $50m but those commitments may be replaced by irrevocable bids:

As reported in its Form 10-Q for the quarter ended June 30, 2012, as of July 30, 2012, the Company had no outstanding auction guarantees. On August 15, 2012, the Company entered into an auction guarantee in the amount of $50 million covering three items that will be offered at an auction in November 2012. The minimum guaranteed price under this auction guarantee is within the range of the aggregate pre-sale auction estimates for the underlying property. The Company’s intent is to attempt to reduce the $50 million exposure under the auction guarantee through the use of irrevocable bids prior to the sale, which is consistent with the Company’s approach to auction guarantees since 2009. However, the Company may not be able to obtain irrevocable bids on terms that are acceptable to the Company.

Sotheby’s (BID) Enters $50M Auction Guarantee for November Auction (StreetInsider.com)