Sotheby's, the auction house, is banking on a $70 million (£36 million) sale of Francis Bacon's 1976 painting Triptych next week to offset what it calls uncertain economic times.

The auctioneer hopes that it will attract as much as $477 million from its sales of contemporary art in New York next week, when Mark Rothko's Orange, Red, Yellow goes under the hammer, possibly for about $33 million.

The auction house a cknowledged yesterday that it had fallen into the red during the first quarter of the year. Sotheby's said revenues had fallen 12 per cent to $129.3 million, resulting in a loss of $12.4 million for the three months to March 31. The group blamed lower auction commissions and higher staff costs for the poor performance.

Amid the economic slowdown in the US, and turmoil on Wall Street, Sotheby's has sought to adjust its business model so that it is less likely to be forced to buy artworks itself if a guaranteed price is not reached during auction.

Sotheby's announced a change in its pricing structure for buyers competing in an auction. A successful bidder will be required to pay a premium on top of the agreed price for a work of art. Sotheby's said that it would increase buyers' final purchase prices by 2 per cent or less on most of the lots it sells.

The group said that it had been trying to reduce its exposure to riskier auctions and “tempered some of our opportunities which led to lower margins where it meant that we could meaningfully shift risk away from Sotheby's”.

The company sought to reassure shareholders that the first quarter of the year was typically a weak period for the auction house and that a slowdown had been expected. However, shares in the group fell 8 per cent yesterday, to $25, having traded as high as $57 in the autumn of last year.

The auctioneer insisted that the art market remained strong and boasted that it had managed to sell a piece by Fernand Léger for $39.2 million, and Edvard Munch's Girls on a Bridge for $30.8 million.

Last month Sotheby's failed to sell a flawless 72-carat diamond in Hong Kong that had a pre-sale estimate of as much as $12 million.

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