The vibrant—some say overheating—Postwar and Contemporary art market will get another jolt of anticipation this week as Sotheby’s and Christie’s unveil the lineups for their spring sales. The rush of new collectors is converging on a limited pool of artists, creating rapid price rises across the board from Postwar masters like Pollock, Judd, and Warhol to young artists seeing breakout gains. No one knows which two collectors will provoke the next price-setting battle over which artist. But price trends can give us some indication of where the market is going.

A spectacular private sale in the last year brought three important Jackson Pollocks to Sotheby’s. Two of the works are on the block as part of larger estates or collections, according to Sotheby’s Contemporary specialist, Anthony Grant. But one seller “is very much aware of what’s happening in the market and what they’ve heard about the private sales,” Mr. Grant said. David Geffen reportedly sold Pollock’s “Number 5, 1948” last November for $140 million. And all eyes will be on “Number 16, 1949” estimated at between $18 million and $25 million.

Masterworks are not the only lots that drive the market. Many collectors are looking for a story to build their acquisition strategy around. That means finding the right young artists destined for a place in art history.

A place in history usually requires a good backstory, such as the one around the new figurative painters associated with John Currin. “People respond to figurative painting,” an art advisor, Abigail Asher, said. “People like when a nucleus is forming. It makes a good story.”

Prices for work by artist Lisa Yuskavage have run up dramatically in the last year based in part on her role in that group. She paints voluptuous women in an exaggerated manner. According to Artnet’s database of auction prices, Ms. Yuskavage’s prices rose dramatically last year. The average price of the 11 works sold in 2006 was over $314,000 — a 288% increase from the year before.

But there is a caveat that should go on any statistic about her work. The 11 Yuskavage pictures auctioned last year far exceeds the 10 pictures sold during the preceding five years. Which has some art advisers calling for caution. “I’ve bought Lisa Yuskavage,” adviser Kim Heirston said. “But I’m not going to advise a client to buy one at $1 million.”

The career of Cecily Brown, another accomplished young painter with soaring prices, shows what dangers come when high prices attract work onto the market. In 2001, four Browns sold at auction for an average price of $52,000. Those prices lured six works onto the market in 2002, but the average price dropped 19%. After some fallow years when few works sold at auction, last year 14 pictures traded hands at a bullish average price of $225,000.

Liquidity cuts both ways. It is also a relative term. Take the case of Donald Judd, whose estate sold 35 works last April. Many in the art world expected the event would flood the market and kill prices. Instead, “the sale gave the Judd market a lot of traction,” Christie’s head of Contemporary Art, Amy Cappellazzo, said. “Everyone thought, ‘Oh the market won’t absorb all those Judds at once.’ But the market was reinforced by them.”

With the floodlight of attention on Judd’s work, collectors and dealers suddenly understood that the Judd market was finite. “That’s everything that’s going to come on the market,” Ms. Asher said. “There are not a lot of dealers you can call and say, ‘do you have a Judd in your back room?’ Go to the fairs. No one has Judd.” Prices rose accordingly by 64.7% in 2006.

Scarcity also creates a trickle down effect. Judd is the master of minimalism, but an artist such as Carl Andre also saw a 161.8% move in prices last year. The late Sol Le-Witt, too, got carried along with the tide. Last year’s 63% upward momentum should continue.

What makes the rising market so difficult to gauge is the range of artists affected. John Baldessari’s prices have risen 286% in the past year. But Baldessari is a bit of an artist’s artist, not a favorite with most new collectors. “He’s a very difficult artist to grasp,” Ms. Heirston said. “It’s nice to see people recognize his important contributions to art history and how much of the new generation of painters he has influenced.”

Other visible but not necessarily household names have also been rapidly increasing in value. Sam Francis is up 138%. John Chamberlain 89%, and Mike Kelley nearly 160%. With action like this, it is surprising that we haven’t seen a futures market emerge for artists and their works.

Other movements have seen this knock-on effect, as well. Lichtenstein and Warhol are the masters of Pop Art, but eight-figure prices have sent collectors looking toward other important Pop painters. Tom Wesselmann, who is represented by several works in the Contemporary auctions this season, has seen a rise of 104% over the last year.

All of these trends come together in the work of Warhol. In 2006, the average price for Warhol rose 48.9% with 258 lots changing hands. Only a few might make a run at a $25 million Warhol, but there are buyers for his work at every level. “If you’re talking about $1 to 4 million,” Sotheby’s Mr. Grant said, “you’re talking about a lot of buyers.” Which has nearly everyone waiting expectantly for the sales in mid-May, including Mr. Grant, who said: “It’s going to be Warhol week.”