Christie’s Postwar and Contemporary department co-head, Brett Gorvy, knows he is in an enviable position. “Christie’s won the major estates this season. That allows us access” to other property, Mr. Gorvy said. Two star collections – 17 works from the Lee V. Eastman collection and eight consigned by collector Edward Broida – boost Christie’s November 8 evening sale of contemporary art to an estimate of $101 million to $145 million. If it comes in toward the high end of the estimate, it would be another contemporary auction record for the house, which drew $133 million in its evening sale last May.

Among the Eastman works are nine by Willem de Kooning, who was one of attorney Eastman’s clients, as well as two small Rothkos, a Franz Kline, and a Motherwell painting; together their low estimates total $17.5 million. The eight works in the Broida collection are worth about $30 million. The highlight of the Broida collection, and the priciest lot in the sale, is Rothko’s “Homage to Matisse,” estimated at $15 million to $20 million. It is closely followed by Roy Lichtenstein’s “In the Car,” estimated at $12 million to $16 million, which was consigned by the artist’s son Mitchell.

Last season, Christie’s also had a prize estate chock-full of postwar masterpieces from Donald and Barbara Jonas. “This has been a team-building effort for five years,” Mr. Gorvy said. He cited the arrivals of Laura Paulson, from competitor Sotheby’s, and Jennifer Vorbach, from powerhouse gallery C &M Arts (now L &M Arts) to the department within the last year and a half as crucial. “When we won Eastman, Broida, or the Lichtenstein, it was first and foremost the team,” he said.

Sotheby’s has no single collection anchoring its November 9 Postwar and Contemporary Art evening sale, which is estimated to bring between $78.6 million and $108 million. It does, however, have nine Warhols and two Cy Twombly paintings, both of which are estimated to break Mr. Twombly’s existing auction record of $5.6 million. The star lot is David Smith’s imposing stainless steel sculpture “Cubi XXVIII,” estimated at $8 million to $12 million.

The highest dollar values at both Christie’s and Sotheby’s sales are all hung on works by the postwar Abstract Expressionists. Such masters as Rothko and de Kooning were first collected by a generation that is now old enough to leave estates behind. “This sale is classic blue-chip postwar painting,” said Loretta Howard of Jacobson Howard Gallery, which deals mainly in postwar works. “That’s nice for me to see, because in past years I saw it change so much and lean so much to very contemporary.”

Still, the Pop artists are catching up, led by Warhol. The sale of his “Liz” for $12.6 million last season at Sotheby’s and the ambitious estimate on the Lichtenstein indicate that a canon is being formed firmly around these artists.

Since 2003, contemporary art has been selling at a feverish pace, in galleries and art fairs as much as auctions. The word “overheated” passes the lips of some dealers. But few think a crash will come this season. “You have to believe in the paintings you have and in the momentum of the market,” Mr. Gorvy said.

But with quality postwar pictures becoming as restricted as those made by the modern masters, prices keep going up, and buyers are moving on to the newest contemporary works. Then there’s the added lure, Ms. Howard said, of “the fun and fashion of things like Art Basel Miami Beach and the art bus that people hop on for social reasons.”

The youngest artists at the auctions, from Chris Ofili to Franz Ackermann, have many years before them, and are still producing; some works have come to auction as few as two years after they were made. Mr. Ofili, 37, who has a big, vibrant 2001 painting in the Sotheby’s sale, recently set an auction record of $1 million, after a few years of selling for around $100,000 on the secondary market.

Serious collectors, Sotheby’s vice-president of Contemporary Art, Alexander Rotter said, know the value of a work on the primary market and will evaluate a piece by a younger artist at auction by how much it goes for at the gallery. “Artists that were previously determined to be undervalued relative to the critical importance, like Richard Prince, quickly become fully valued,” a Manhattan dealer, Perry Rubenstein, said.

But for some artists, such as Maurizio Cattelan, there can be such a thing as too much acclaim. Mr. Cattelan’s auction prices jumped into the $2 million to $3 million range in 2004, but his work has faltered at auction since. The specter of speculative buying hangs over other contemporary artists.

“It is very dangerous for the work of young artists to appear too quickly in an auction,” Mr. Rubenstein said. “Their work is not to be treated as new issuance or an IPO.” In the past half-decade, art funds have formed to use art as investments, and online indexes now track the rise and fall of an artist’s value. Even with all that, however, Mr. Rotter said he doesn’t know collectors who buy art purely for investment. “The initial reaction is still, do I like it or not.”

Highlights of the Postwar and Contemporary Art Sales

Christie’s (November 8 & 9 )

Mark Rothko, “Homage to Matisse” (1953)
Estimate: $15 million to $20 million
Rothko strove to imitate no one, but he was fine with acknowledging a debt to Matisse, through a rarely used title and through the bright, sun-inflected colors of this wall-size painting. The painting, from the collection of Edward Broida, who has promised much of his collection to MoMA, hung in Rothko’s own home until his suicide in 1970.

Roy Lichtenstein, “In the Car” (1963)
Estimate: $12 million to $16 million
This prime-period Lichtenstein was part of his first major exhibition at Leo Castelli Gallery in 1963. As shockingly mechanical as the comic strip appropriation appeared at the time, the painting still shows traces of the hand in its Ben Day dots and white streaks over stray marks. It is being sold by the artist’s son, film producer Mitchell Lichtenstein. While the record for a Lichtenstein work sold at auction is $7.2 million, Christie’s department head, Brett Gorvy, said there have been private sales for around $20 million.

Francis Bacon, “Study for a Pope I” (1961)
Estimate: $7 million to $9 million
Bacon’s riff on Velazquez’s “Portrait of Pope Innocent X” radically abstracted the background and torqued the image of the diseased pope into a searing indictment of corrupted power. After a lull in the mid-1990s, Bacon’s prices have been soaring, with a record of $9 million set in June in London.

William de Kooning, “Untitled” (1977)
Estimate: $4 million to $6 million
This is the star lot of the collection of Lee V. Eastman, the entertainment lawyer who was father to Linda Mc-Cartney and attorney to the Beatles, de Kooning, and Josef Albers. Its big, swirling aquamarine and fleshy pink brushstrokes make for a high point of de Kooning’s late work made in East Hampton.

Philip Guston, “Zone” (1953-54)
Estimate: $4 million to $6 million The dense, almost woven textures and misty colors of this mid-career abstraction will be familiar to any who dropped in on Guston’s Met retrospective two winters ago. In a 1952 interview, the artist said that an inspired painting should put a viewer “in a state of reverberation,” then went out and did it. This painting also comes from the Broida collection.

Jeff Koons, “Self-Portrait” (1991)
Estimate: $2 million to $3 million
Jeff Koons shows much about his intentions in this over-the-top bust of himself. He has squared his jaw, fluffed his hair, pointed his chin toward the heavens, and put himself on a bed of crystalline marble that directly references Bernini’s “Ecstasy of St. Theresa.”

Sotheby’s (November 9 & 10)

David Smith, “Cubi XXVIII” (1965)
Estimate: $8 million to $12 million
This is one of the last chances buyers will have to compete for what’s considered one of the most important sculpture series of the 20th century. Smith made 28 Cubi, all large-scale stainless steel constructions based on rectangular and square forms. Of those, 21 are owned by museums. Smith’s past record is $4 million, but that was set back in 1994 for another Cubi.

Andy Warhol, “Jackie Frieze” (1964)
Estimate: $8 million to $10 million
Thirteen grieving Jackies, all based on the same photo of the former first lady in a veil, scroll in a line like an unfurled film reel. Even though it depicts one of Warhol’s favorite pretty women, “this is a real disaster painting,” a Sotheby’s specialist, Alexander Rotter, said.

Cy Twombly, “Untitled (Rome)” (1961)
Estimate: $6 million to $8 million
Two paintings from the expat painter, who has lived in Rome since 1957, are peak examples of his best series. The Rome painting has a surface worked up into a tactile pink lather. It has also been in a private collection since the year after it was painted.

Cy Twombly, “Untitled (New York City)” (1968)
Estimate: $8 million to $10 million
The second Twombly, from his blackboard series, features looping scribbles, which descend like clef notes or Duchamp’s nude on a staircase. The low estimates for both Twomblys would set a new auction record for the artist, which currently stands at $5.6 million.

Jean-Michel Basquiat, “El Gran Espectaculo (The History of the Black People)” (1983)
Estimate: $4.5 million to $6.5 million
One of the centerpieces of the current traveling Basquiat retrospective, this three-part stretcher painting is labeled in the retrospective as belonging to Paris dealer Enrico Navarra. It’s grandscale history painting done in the style of an East Village griot.

Damien Hirst, “The Most Beautiful Thing in the World” (2003)
Estimate: $950,000 to $1.2 million
A Hirst butterfly painting failed to sell in October’s London auctions, but this large work, encased in an artist-created round frame, is more elaborate, a mosaic of butterfly wings arranged like a symmetrical mandala. There are conservation issues with some older butterfly paintings, but in later works Mr. Hirst seems to have solved the problem of falling butterflies.