It will be hard for this week’s sales of contemporary and postwar works to top the results the big auction houses netted last spring. In May, Contemporary art seemed hotter than even the Impressionist and Modern material then flying off the block. Christie’s set nine artists records at its spring sale, pulling in a whopping $102 million. Meanwhile Sotheby’s totaled a lesser $65.7 million, but sold 100% of it material – the first time it had ever done so. Phillips, de Pury & Co. scored with more recent, and less expensive, material, outstripping its high estimate to total $17.7 million.

This time around Phillips has ramped it up, fielding two sales (a single-owner photography sale “Veronica’s Revenge” tonight and a various-owner contemporary sale on November 12) expected to total $33.4-46.8 million. The Christie’s and Sotheby’s evening sales are neck-and-neck in terms of presale estimates, though dealers say Sotheby’s has the better sale. Sotheby’s projects $78-107 million for its sale tomorrow; Christie’s hopes to bring in $69-94 million the next day.

The big question is whether prices will continue to climb, or if we have hit a peak. Among the older works sold last week, the best set records, but otherwise the market seemed measured, supporting a high volume but not spectacular prices.

“The market is in a really strong place, which makes me really nervous,” said senior director of the Marian Goodman Gallery, Jeannie Freilich. “I don’t know how long this can sustain.”

Phillips begins with a highly anticipated sale, “Veronica’s Revenge,” a single-owner photography collection put together over the last decade by Baroness Marion Lambert and estimated at around $10 million. With a great eye and a greater budget, Ms. Lambert bought the works for the Geneva headquarters of her husband’s bank. Ultimately the collection was not installed there but sent on tour to museums.

Ms. Lambert’s essay at the front of the catalog lashes out cryptically at “my much regretted brother-in-law,” and a Geneva politician she calls “a narrow-minded bureaucrat.” She also writes of personal tragedy, which she says precipitated the sale: “My daughter’s untimely death, as a result of the devious and criminal acts of a perverse individual (unpunished because of the statute of limitations, but not acquitted) left this collection without a future.”

The collection has generated considerable presale buzz, and on Saturday dozens of fashionable art mongers – spiky hair, Gucci sunglasses, and exotic accents – trolled Phillips Chelsea gallery, sipping Champagne and leaving bids. Of the 184 lots in the sale, most are by artists now considered stars. Ms. Lambert’s favorites included Cindy Sherman, Hiroshi Sugimoto, Matthew Barney, Richard Prince, Thomas Ruff, and Roni Horn. Dealers say this sale will have historic importance and establish watershed prices for these artists.

“While we are not so far off in history, this is a very important moment in photography” said private dealer Sharon Coplan.” Baroness Lambert collected with a discernable eye, picking key pieces and key artists.”

Others have suggested that, whatever Ms. Lambert’s motivation in selling is, her timing is brilliant. Dealers suspect the souped-up market is poised for a downturn, but tonight’s sale might prove it has more staying power than expected. Stay tuned.

On Tuesday Sotheby’s follows up with a strong array of postwar material, including a stunning 1954 Mark Rothko, “No 6. (Yellow, White, Blue over Yellow on Gray)” estimated at $9-12 million. “It’s as good as it gets,” said Los Angeles dealer James Corcoran, who sold the painting to Pennsylvania collectors Dennis and Gisela Alter in 1994 when he was a co-owner of C &M Arts (he’s the C). The Alters subsequently sold the painting and are not the consignors.

Sotheby’s other highlights are several works from music mogul David Geffen. Mr. Geffen is among the top postwar art collectors in the world, so even his castoffs are highlights. He is selling three works by Jasper Johns – two small paintings and one large drawing. The paintings include the 1956 9-inchby-9-inch “Green Target,” a wax and newspaper collage, and the monumental 1961 drawing “0 Through 9,” which is estimated at a very bold $7-9 million.

Sotheby’s also continued the two-week trend of paying consignors hefty guarantees. The Rothko is guaranteed, as are three splashy paintings consigned by dealer Alberto Mugrabi. They include Andy Warhol’s 1963 “Red Car Crash,” estimated at $5.5-6.5 million, Jeff Koons’s 1995-98 “Bracelet,” estimated at $1-1.5 million, and Jean-Michel-Basquiat’s 1982 “Offensive Orange,” estimated at $2.5-3.5 million. “It’s a sexy group of paintings,” said Sotheby’s expert Matthew-Carey Williams.

Christie’s has also put its money on the line, guaranteeing a collection of modern and contemporary artworks spread over sales last week and this week. Those in the trade said Paul and Dorie Sternberg were given a $32 million guarantee for their consignment, which grossed only $8.7 million last week (a Leger and a Giacometti both failed to sell). Christie’s still needs $23.3 million for the remaining seven lots, including $5-7 million for the cover lot by Cy Twombly.

Big money is also backing Andy Warhol’s “Mustard Riot Race,” estimated around $15 million, a large 1963 diptych with image taken from a Life magazine story. The left side is repeating images from the protest and the left side is a blank panel. Warhol reportedly told friends he added the panel, making the artwork twice as large, and therefore twice as expensive.

While the sale has strong examples from many of today’s hotshots – John Currin, Maurizio Cattelan, Andreas Gursky – and also three great minimalist pieces – Carl Andre, Donald Judd, and Dan Flavin – one of the pieces sure to blast its estimate is Robert Motherwell’s 1961 “Elegy to the Spanish Republic No. 71,” from his famed series of over 200 works based around a static black and white set of forms. These works rarely come on the market. This version is being sold by the Yale Art Gallery. The estimate of $600,000-$800,000 should be easily surpassed.