It's fall. Leaves in Central Park are golden and so are profits in the art world, as Christie's and Sotheby's prepare to auction off $2 billion worth of works in New York.

From November 4 to 12, the two auction houses go head to head in selling hundreds of pieces of modern, impressionist, post-war and contemporary art, six months after the spring season smashed a string of records and netted more than $2.6 billion. Fuelled by rising demand from Asia and the Gulf, it was 10 days of eye-watering extravagance that set a new world record for any work of art sold at auction -- $179.4 million for a Picasso.

"Buyers in the art market have never been more diversified," explained Michael Macaulay, head of evening sales in contemporary art at Sotheby's. "Ten years ago you'd say an American abstract expressionist painting is probably going to end up in the States but I think now genuinely, as never before, it could go to any corner of the world."

Sotheby's kicks off the season by selling the private collection of the American philanthropist Alfred Taubman but it is rival Christie's that grabs the headlines with two top lots. The work estimated to be the most expensive is a sensuous nude by Amedeo Modigliani valued at $100 million, followed by an iconic pop art masterpiece from Roy Lichtenstein estimated at $80 million.

Modigliani's "Reclining Nude" comes to auction for the first time, expected to set a new record for the Italian artist. The picture of the naked woman reclining on a luscious red couch and blue cushion, painted in 1917-18, provoked a scandal when it was first exhibited in Paris. "It is unquestionably a masterpiece," said Jessica Fertig, co-head of the Christie's sale. Christie's believes Lichtenstein's "Nurse" -- a shocked looking blonde with sexy red lips -- could also fetch more than $100 million, which would nearly double the artist's current record.

That would make it a shrewd investment for its most recent owner, who acquired the comic book-inspired portrait for $1.65 million in 1995. US billionaire and Republican party donor, Bill Koch, can also expect a giant windfall. He is parting company with Picasso's "La Gommeuse," the portrait of a cabaret artist dating back to 1901 when the artist was just 19 years old and grieving the suicide of a close friend.

Koch bought the canvas for $3 million in 1984. Sotheby's expects it to fetch around $60 million. Not only that, but Koch got two for the price of one. In 2000, he discovered that there was another painting on the reverse -- a mocking depiction of Picasso's art dealer -- that had been hidden under the lining for a century. Koch is also parting company with a Monet Water Lilies piece, which Sotheby's is selling on November 5, valued at $30-50 million.