(Bloomberg) Works by Andy Warhol and Damien Hirst will lead contemporary-art sales in London next month that may raise at least $76 million and test a fragile market recovery, dealers said.

Increased volumes have boosted estimates at Christie's International, Sotheby's and Phillips de Pury & Co. auctions during London's "Frieze Week" to about double the level of last year. The market is struggling to regain momentum after buyers shunned overpriced lots in the summer.

"We've tried to put the brakes on slightly," Francis Outred, Christie's European head of contemporary art, said in an interview. "Demand was becoming more selective in June. We've been advising sellers not to push too hard with their estimates and let the market decide."

On Oct. 14, Christie's will be offering a Hirst "butterfly" painting from 2006, "I am become death, shatterer of worlds." The 17 foot (5 meter) abstract is estimated at as much as 3.5 million pounds, making it the most valuable work by the artist to have appeared at auction since 2008.

Another Hirst butterfly of the same size sold for 4.7 million pounds at Phillips in October 2007. The seller of this latest work to be offered, featuring two circular explosions of color inspired by nuclear physicist Robert Oppenheimer's quotation from the Bhagavad Gita, is an American collector, Christie's said.

Hirst's Zenith

Few high-value works by Hirst have appeared at auction since Sotheby's 111.5 million-pound "Beautiful Inside My Head Forever" sale in September 2008 marked the zenith of the artist's commercial success. At that two-day event, which coincided with the collapse of Lehman Brothers Holdings Inc., 24 works attracted prices of more than 1 million pounds. No pieces by Hirst have reached that level at auction in 2010.

Christie's estimates its 51-lot evening auction will raise at least 15.95 million pounds, more than double the 6.8 million pound low estimate of its 25-lot sale last year.

The auction will include three pieces exhibited at Charles Saatchi's "USA Today" show of young American artists at the Royal Academy in 2006. Paintings by Mark Bradford and Kelley Walker are estimated to sell for as much as 300,000 pounds and 700,000 pounds apiece. Christie's declined to confirm Saatchi is the seller. The auction house yesterday named Steven Pleshette Murphy as chief executive to succeed Ed Dolman, who was promoted to chairman.

Like Christie's, Sotheby's has this year chosen to offer 20th-century Italian works -- traditionally sold in the week after Frieze -- on the same evening as contemporary art.

"People are in town for three or four days maximum during Frieze," Cheyenne Westphal, Sotheby's European chairman of contemporary art, said. "It's better if you can present all the material together at the same time."

Warhol's Diamonds

Sotheby's Oct. 15 evening offering of 40 lots carries a low estimate of 10 million pounds. The most valuable work is the vibrantly colored 1980 Warhol silkscreen, "Diamond Dust Shoes." Never offered at auction before, this is estimated to sell as much as 1.6 million pounds.

The sale also includes six works entered by Jerry Hall. Lucian Freud's 1997 oil-on-canvas "Eight Months Gone," depicting the model reclining nude while pregnant with her fourth child, Gabriel, carries an estimate of 300,000 pounds to 400,000 pounds. The 1965 Frank Auerbach canvas, "Head of Helen Gillespie IV," is expected to fetch as much as 900,000 pounds.

Optimistic Estimates

In May, average prices at Sotheby's and Christie's evening sales of contemporary works in New York were more than double what they achieved at equivalent auctions in 2009. A month later in the U.K. capital, the rate of increase slowed to 46 percent, according to the London-based research company ArtTactic. Over- optimistic estimates led to an increased number of lots falling short of expectations, said dealers.

Phillips estimated its evening sale of 56 lots on Oct. 13 may raise at least 6.5 million pounds. The equivalent event last year, containing 43 works, carried a low estimate of 5 million pounds. The most valuable piece in the sale is the 1978 David Hockney six-part watercolor, "Autumn Pool," from the "Paper Pool" series, valued at as much as 1 million pounds.

The following day, Phillips will hold a 148-lot sale of more affordable contemporary works. This offering carries an estimate of 2.1 million pounds to 2.9 million pounds.