It's Frieze, the art fair where aficionados and amateurs open their wallets

Giant French horns, Tracey Emin's pink neon signs, Kate Moss portraits and banknotes defaced by Jake and Dinos Chapman will jostle for attention at Frieze Art Fair, which opens in London's Regent's Park today.

Multi-million pound deals are set to be brokered by more than 150 gallery owners ranging from New York's Larry Gagosian to London's Jay Jopling and Zurich's Iwan Wirth. Charles Dupplin, chairman of the art division at Hiscox Artprojects, estimated the value of the fair could total as much as £125m.

As the fair opened for sales to art market insiders yesterday, the Tate was among the more prominent British buyers, using its dedicated "Outset" fund of £150,000 to purchase four works which will be exhibited at Tate Modern on London's South Bank next month. The works are a large installation by the Polish artist Pawel Althamer, Mauro Restiffe's series of grainy black and white photographs of urban scenes, a three-metre tall windmill sculpture entitled Moulin Rouge by the German artist Andreas Slominski, and Armando Andrade Tudela's Altered House, a slide projection featuring a palimpsest of architectural exteriors and interiors. Neither Slominski nor Restiffe were in the Tate's existing collection.

Nicholas Serota, the Tate's director, said the gallery had set out to buy works by Eastern European and Latin American artists, and that the fair provided an opportunity to view the best works by young unknown artists. "We went in wanting another installation by Althamer but we suddenly came across the Slominski which felt exactly right for our collection. We don't come to Frieze to buy works by artists that are already established. The purpose is to concentrate on emerging and international artists and I'm quite certain that someone like Pawel Althamer is one of the most important artist of this coming decade," he said.

Previous debut works that have been bought by the Tate from Frieze in past years have included a piece by Olafur Eliasson in 2003, the same year that the Tate's Turbine Hall showcased the artist's Weather Project. They have also picked up works by the Turner Prize nominee, Simon Starling, the Turner winner Jeremy Deller and a work by Martin Boyce.

Although the primary focus of the fair is commercial, it is also about providing visual entertainment and raising the public's appetite for the best of contemporary art, according to Frieze organisers who predict that more than 63,000 people could come to scour the park's pavilions over the next few days.

About 80 per cent of visitors who come to view sculpture, paintings and installations from more than 28 countries, will not end up buying any of the works on offer, whose prices range from £500 to £500,000.

Yesterday, the fair presented seven specially commissioned art projects or conceptual performances. They included the Chapman brothers' effort at drawing their own "graffiti" on people's banknotes at the White Cube gallery stand.

Another project by the American artist, Richard Price, featured an installation of a car with a bikini-clad model draped across it, hailed as a metaphor for the art dealing market, while Gianni Motti presented his performance piece of a policeman performing yoga.

There was also plenty to occupy the interest of serious collectors. Georg Baselitz's dealer, Thaddaeus Ropac of Paris and Salzburg, was selling a 63-inch-high painted bronze, booted leg, entitled "Pace Piece", for €320,000, while most items at the stands of the biggest dealers were sold within the first few hours. Most pieces from David Zwirner gallery in New York were sold within minutes.

Frieze highlights

Mauro Restiffe's Empossamento series, Casa Triangulo Gallery, Sao Paulo

A series of 11 black-and-white photographs featuring cityscapes and urban scenes at a seminal historic moment in Brazil's history.

Claes Oldenburg and Coosje van Bruggen's French Horns, Unwound and Entwined, Waddington, London, and Pace Wildenstein Gallery, New York

Oversized stainless steel musical instruments painted bright yellow which dominate the 'sculpture park' section of the art fair.

Julian Opie's Kate Moss portraits, Lisson Gallery, London

Painted in pop-art style by Opie, with images of her in profile and facing the viewer wearing an enigmatic smile.

Martin Honert's Giants at Gallery Johen, Berlin

Giant 12ft woodsmen sculptures dressed in jeans, hoodies and sporting rucksacks and walking sticks.