Art sales: over-talented and over here Telegraph

Young American art is taking London by storm this autumn – not in the salerooms, but in our public institutions and private galleries where, behind the scenes, a new, potentially volcanic market is bubbling.

Already up and running is Uncertain States of America, an exhibition at the Serpentine Gallery of works by 40 artists in their twenties and thirties that reflect the social and political unease felt by those in the post-9/11 era. One of these, Matthew Ronay, is also having a solo show at Parasol Unit, a privately funded gallery in north London.

In London's West End, dealer Thomas Dane quotes Salman Rushdie in the introduction to Civil Restitutions, his show of socio-political art that includes both older and younger American artists: "A moment comes, but rarely in history, when we step out from the old to the new."

And next month Modern Art, a fashionable gallery in east London, will exhibit new work by Matthew Monahan, an ubiquitous presence at this summer's Basel Art Fair, so obviously an artist to be watched. This show will benefit from Monahan's inclusion in the biggest display of confidence in young American art yet: USA Today, Charles Saatchi's blockbuster exhibition of 150 works by 40 young American artists that opens at the Royal Academy on October 6.

Where Saatchi moves, there is usually a fertile market at work. When he began buying these works two years ago there was less than a handful of collectors exploring the terrain. One was Manchester businessman Frank Cohen, dubbed the Saatchi of the North, who worked closely with the London-based dealer and collector Nicolai Frahm. Others were Don and Mera Rubell from Miami, who make a habit of setting trends in the market place, and sensed a new "zeitgeist" in the air. The Rubells will show their collection of art from Los Angeles during the Art Basel/Miami Beach art fair in December.

But museum exposure for these artists, particularly in New York at the Whitney Museum of American Art and the radical, publicly funded PS1 gallery, alerted a much wider range of collectors, all eager to jump on the next bandwagon, and prices began to escalate on the private resale market. This is a market that operates after the first point of sale behind closed doors: deals are struck between collectors or in dealers' back rooms – not in the saleroom.

Frahm, who showed a group of Los Angeles artists from his and Cohen's collections at the Hospital gallery in Covent Garden this summer, confirms what has been happening. Three years ago he commissioned Gerald Davis (who is in Saatchi's exhibition) to paint a triptych and paid £3,000 a canvas. Gallery prices for Davis in New York are now more than £30,000 a canvas, but on the private resale market his best works can command up to £100,000, says Frahm. The Los Angeles photographer Florian Maier-Aichen (also in the Saatchi show) was selling his work at London's Victoria Miro gallery last year for between £10,000 and £15,000. His best work is now reselling privately for more than £60,000.

Other artists in USA Today whose names may mean little to us right now but can command six-figure sums include Kristin Baker, Mark Grotjahn, Banks Violette, Terence Koh, Wangechi Mutu and Barnaby Furnas. Two of the most sought-after are the painter and sculptor Jules de Balincourt, and the painter Dana Schutz. Four years ago, you could buy de Balincourt's work for under £1,000. Now, trade sources say, his best work can resell privately for up to £400,000, while prices for Schutz paintings that cost less than £30,000 two years ago can be as much as £450,000. But New York dealer Zach Feuer, who represents both artists, says these figures are exaggerated: "People may be asking those prices, but it's not true that they're selling for that much."

Nevertheless, such talk points to a hyperactive resale market for many of the artists in the Saatchi show. As yet, most have still to reach the auction rostrum, and only one so far has made an impact in the saleroom – a large painting by Furnas doubled estimates to sell for £210,000 this May.

For the others, and indeed for Saatchi's latest gamble, the acid test has yet to come.