At New York City’s big-money art auctions in May, the most dramatic price spikes are expected to be at the top end—much like last year, when billionaires clashed over Picassos and negotiated privately for Pollocks.

The summer of 2006 saw cosmetics mogul Ronald Lauder pay a breathtaking $135 million for Adele Bloch-Bauer I, a shimmering gold 1907 painting many people had never heard of. This was reported to be the highest price ever paid for an artwork. The sale catapulted Lauder and the Austrian painter Gustav Klimt into the headlines.

Such is the potential power of billionaire money to bring a torrent of publicity to an individual artist. But even more significantly, when a deep-pocketed buyer develops a jones for a particular period or style, he or she can shift a whole segment of the market. Other collectors start eyeing similar works, asking prices rise, and prime pieces suddenly become available.

“The rules change when you have Ronald Lauder going after a Klimt for an unheard-of $100 million-plus number,” says Howard Godel, a New York City-based dealer in American art. “It has to change people’s thinking as to how high is high.”

Rich and aggressive buyers are not exactly a new phenomenon. J.P. Morgan, John D. Rockefeller Jr., and Joseph Widener drew gasps 80 years ago by paying top dollar for then-chic old masters paintings. What has changed is the sheer number of mega-wealthy buyers, from Beijing to Los Angeles to London. Combined annual sales at Christie’s and Sotheby’s have risen 63.5 percent over the past three years. A 2007 investor report from Sotheby’s notes that 68 of the 100 people designated by Forbes as the richest in the world are clients of the house. In March, 71,000 visitors trekked to Tefaf Maastricht, a major art and antiques fair held in a remote Dutch town; 305 arrived on private jets.

In some areas, such as postwar and contemporary art, the field of buyers is vast. But a number of collecting categories—modern Austrian art, for one—are directly impacted by just a handful of bidders with outsize influence.

It’s impossible to predict what (or who) this spring’s blockbuster will be. But a few examples make clear how profoundly the landscape can change.

Expressionist German and Austrian art
Though beloved by some, Klimt paintings were not the hottest items on the art market until Lauder bought his record-setting picture. Then prices soared. The previous high for a Klimt had been $29.1 million, paid in 2003 for the landscape Landhaus am Attersee. That’s far from chump change, but nowhere near the $87.9 million a less dazzling work, the portrait Adele Bloch-Bauer II, fetched at Christie’s last November. (Lauder has said he was not the buyer.)

Lauder’s interest in German and Austrian art has encouraged other collectors to consider this historically neglected field. Because American museums and collectors largely avoided the art form following World War II, Lauder was able to assemble his collection over the years at relatively low prices. In 2001, he founded a boutique museum, the Neue Galerie, on Fifth Avenue in New York City, which has helped increase the visibility of lesser-known artists such as Egon Schiele, Oskar Kokoschka, and designer Josef Hoffmann.

But Lauder’s efforts on behalf of German and Austrian art might ultimately make it harder for him to buy prime examples. “There is no doubt he has created competition for himself,” says dealer Andrea Crane, who believes the field is now experiencing a renaissance. She is quick to add, though, that Lauder sometimes scares off rival collectors: “I’ve had many people say to me, if I’m bidding against Lauder, I may as well not even bid.”

Islamic art
For a few glorious years, Sheik Saud al-Thani was probably the biggest art collector in the world.

A member of Qatar’s royal family, al-Thani had the coffers of the oil-rich Gulf country at his disposal. He spent more than $1 billion on Islamic art, stockpiling rare 17th-century Iranian tiles and Mughal Empire daggers for a series of museums planned for Qatar. In the process, some dealers and auction-house executives say, he inflated the market for Islamic art.

According to Joseph Coplin of Antiquarium Ltd., in New York, the finest-quality glass beads, Roman glass, Roman marbles, and Egyptian antiquities were selling for three, four, and five times their high estimates at auction at the time al-Thani was collecting. Coplin emphasizes, though, that someone had to be willing to bid against the sheik in order for prices to have escalated in such a way.

“Everyone benefited from Saud’s appetite for antiquities,” says New York City dealer Hicham Aboutaam, of Phoenix Ancient Art. “It’s a classic situation. A newly prominent buyer emerges and art owners respond by offering pieces they hadn’t previously considered selling.”

Saud al-Thani also indulged his own collecting fancies, in 2002 purchasing a Roman statue of Venus at Christie’s for $11.7 million, more than two and a half times the $4.4 million high estimate. It was the highest price ever paid for an antiquity at auction, and Aboutaam says that, had al-Thani not bid, the price would likely have been 30 to 40 percent lower.

In 2005, the sheik was removed from his post as chairman of the National Council for Culture, Arts, and Heritage, reportedly over concerns about his outlandish spending. But dealers say that wasn’t the only problem; artworks like the nude Venus weren’t appropriate for Muslim audiences and fell outside the council’s mission. Inflated invoices from dealers also raised questions about al-Thani’s conduct. The sheik was placed under house arrest while his cousin, the emir, reviewed the situation. The sound of dealers weeping could be heard around the world.

Fortunately for the trade, al-Thani recently resumed collecting. He is no longer head of the council, but he continues to buy—albeit with a much smaller budget—in other categories he loves, including Egyptian antiquities.

American painting
There were plenty of billionaires chasing American art before Wal-Mart heiress Alice Walton got in the game. In 1998, for example, Bill Gates paid around $30 million for a 19th-century Winslow Homer seascape.

But the stakes rose in 2005 when Walton anted up a reported $35 million in a sealed bid for Asher B. Durand’s Hudson River School masterpiece Kindred Spirits, sold by the New York Public Library. At the same time, Walton announced she would establish Crystal Bridges, an American-art museum in Bentonville, Arkansas. It is scheduled to open in 2009.

Though Walton had been collecting American art for more than 15 years, the museum project prompted her to buy more, and more quickly. The publicity surrounding her purchases and the billions behind the Wal-Mart fortune spurred a dramatic upswing in prices at American-painting auctions. A quick look at the sales at Sotheby’s alone demonstrates a spike. From 2001 to 2003, sales of American paintings accounted for $179.5 million. Over the following three years, the total jumped to $410.5 million.

This is not to say that Walton caused the price surge all by herself, but she has been a factor. “There are 15 to 20 active billionaires,” says Godel of the market for American paintings. “But here’s the scary thing: There’s another 20 behind them, a 20 who will pop up for the right picture on the right day.”