Auction house Sotheby's Inc. reported Friday a third-quarter net loss from continuing operations of $20.9 million, of which $14.6 million were lost on auction guarantees at its impressionist-art sale this week.

The mean estimate of analysts polled by Thomson Financial was for a loss of 30 cents a share, reports Forbes on its website. Operating revenue for the New York-based art retailer rose 48% to $85.1 million, above the $79.2 million analyst estimate. The company said revenue rose on higher commissions from auction revenue and private sales.

The auction Wednesday evening took in $269.7 million, including commissions, but was still a third less than the low presale estimate of $401 million. Not all the artwork was sold. Of the 91 lots auctioned, seventeen failed to sell, among these being a Cezanne estimated at between $12 million to $16 million and an August Macke estimated at up to $25 million, according to media reports.

The Los Angeles Times reports that the company had promised sellers fixed prices for works by Van Gogh, Pablo Picasso and other artists, regardless of whether the pictures sold or not.

Sotheby's shares plunged $14.23, or 28%, to $35.84 on Thursday. The stock had hit a record high of $57.64 on Oct. 10, reports the Times.

The paper also notes that Sotheby’s decision to hand out guarantees was a risk at Wednesday’s impressionist-art sale. These were given for art with an estimated price range of $153 million to $209 million before commissions, based on data in the sale catalog, analyst Kristine Koerber of JMP Securities told the Times.

Of 26 lots guaranteed, five failed to find a buyer and 10 sold below Sotheby's estimated range, Koerber said.

Apart from the above-mentioned Cezanne and August Macke, other paintings that received no bids were Van Gogh's “The Fields (Wheat Fields),” valued at $28 million to $35 million and Georges Braque's “L'Echo,” estimated to sell with as much as $20 million. Both carried guarantees.

Compared to last year, Sotheby’s posted a net loss from continuing operations of $30.4 million, or 49 cents a share, on revenue of $57.4 million.