Rothko's painting is being displayed at Sotheby's in London until 20 April

Francis Bacon's study of Pope Innocent X and a Mark Rothko painting - which are together expected to make up to $70m (�35m) - are on show at Sotheby's.

The two works are among dozens to be sold in New York next month by both Sotheby's and its rival Christie's.

A sale of Impressionist art, including works by Matisse and Cezanne, on 8 May is also expected to command large bids.

A Cezanne watercolour is estimated to make up to $18m (�9m), while a reclining nude by Henri Matisse could fetch as much as $20m (�10m) at the Sotheby's sale.

Supremacy

The 1950 Rothko canvas to go under the hammer on 15 May comes from the private collection of US banker David Rockefeller, and could be sold for $40m (�19.9m).

NEW YORK ART SALES 8 May - Sotheby's Impressionist and Modern sale, featuring Cezanne, Monet and Gauguin 9 May - Christie's Impressionist and Modern sale, featuring Picasso, Cezanne and Matisse 15 May - Sotheby's Contemporary art sale, featuring Rothko and Bacon (above) 16 May - Christie's Post-War and Contemporary art sale

Francis Bacon's painting is considered the star lot of the same auction, and is tipped to break the record for the artist with a sale value of up to $30m (�15m).

The vivid red work is based on Renaissance artist Diego Velazquez's 1650 portrait of of Pope Innocent X.

Two works by abstract artist Jackson Pollock featuring his famous drip-and-pour technique will also be among the lots at the auction.

But they will not exceed the reported $140m (�70m) one of his paintings commanded last year - the highest price ever paid for an art work.

Sotheby's and Christie's have continued to vie for supremacy in the art auction market in recent years, with Christie's securing the largest single sale in history in 2006, worth $491m (�245m).