Sotheby’s to Pay $148.8 Million for N.Y. Gallery : Art: Purchase by auction house is being called the biggest art deal ever, in terms of number and value of paintings.

Sotheby’s auction house has announced that it will buy the contents of a Manhattan gallery for $142.8 million in what may be the biggest art deal ever, both because of the number of paintings and their value.

Sotheby’s will acquire one of the great inventories of 20th-Century art when it buys the 2,300 works from the Pierre Matisse Gallery in a joint venture with William Acquavella, a New York art dealer.

Until now, Sotheby’s has represented art sellers, putting up for auction works owned by others and taking a commission from the sale.

With the acquisition of the Matisse Gallery works, Sotheby’s will be in the business of owning the art it sells, rather than operating in the auction house’s traditional manner of representing sellers.

Acquavella will be managing partner of the joint venture company being set up with Sotheby’s, to be called Acquavella Modern Art.

“As far as I know, it is the biggest art deal both in the number of paintings and the art value that has been done in the art world,” Acquavella told the New York Times in a story in today’s edition.

The gallery’s inventory of 2,300 works by artists including Joan Miro, Alberto Giacometti and Marc Chagall is being sold by the estate of Pierre Matisse, an art dealer and son of painter Henri Matisse. Pierre Matisse died Aug. 9.

Some of the artworks will be sold at auction. But Acquavella said he also plans to have exhibitions around the world and to work with dealers in different countries to sell the works privately.