Christie’s International’s first- half sales increased 15 percent to a record, boosted by auctions of contemporary works by artists such as Andy Warhol.

The London-based company was also helped by growing private sales, demand in Asia, and a 30 percent growth in the number of successful lots. It sold 2 billion pounds ($3.2 billion) of art and antiques worldwide in January through June, the most for any half-year in sterling, Christie’s said today.

“Sales have increased across a range of departments,” Steven P. Murphy, chief executive officer, said in an interview. Lots priced between 500,000 pounds and 1 million pounds were in demand, with average selling rates of more than 90 percent, he said. “While a small percentage of clients buys for investment, we’re seeing a general cultural shift toward art,” he said.

A Warhol self-portrait priced at $38.4 million was the top performer in the first half. Contemporary art fetched 431.1 million pounds, a 40 percent increase on 2010. This was more than in 2008, though not as much as in the first half of 2007.

“The contemporary market has returned,” said Murphy. “It’s done so for a wide range of names,” he said, countering perceptions that the auctions were over reliant on established postwar artists. Works by Warhol accounted for more than $90 million of sales at its New York evening auctions in May.

Sales of modern British art and prints grew by 257 percent and 73 percent respectively. London was Christie’s biggest auction center, with 607.7 million pounds of transactions.

Private Sales

While private sales rose 57 percent to 286.7 million pounds, no single auction item exceeded $40 million. Impressionist and modern-art sales declined 30 percent. Auctions in the Americas dropped 13 percent because of a shortage of collections. In May 2010, a record $106.5 million was paid in New York for a Pablo Picasso painting from the estate of Los Angeles philanthropist Frances Brody.

Hong Kong sales grew 48 percent to 296 million pounds, consolidating Asia as the third-biggest sales center. Worldwide sales of Asian art took 356.7 million pounds, up by 45 percent.

An Asian private client was the buyer of a Michelangelo drawing for 3.2 million pounds in London on July 5. Chinese buyers continue to be the largest group at international wine auctions, which increased 107 percent to 28.7 million pounds.