Claude Monet, Nymphéas, 1907, oil on canvas, 39 3/8 by 32 inches. For sale May 6 at Christie's New York, est. $25-$35 million. Photo Christie's Images Limited 2014.

Over $680 million in Impressionist and modern artworks will go on the auction block next month during the New York evening sales at Christie's and Sotheby's.

The two houses are always in competition for the best material, and Christie's appears to have the bigger haul; its May 6 sale is expected to bring in between $245 and $360 million for 54 works. Sotheby's auction the following night, despite having 18 more works, is estimated at $220 to $321 million. The high estimates are fueled by some estate material that is fresh to the market.

Going into the twice-yearly Impressionist and modern art sales, market watchers often bemoan the shortage of high-quality examples, but in recent phone interviews with A.i.A., several New York dealers were optimistic.

"It's a good pair of sales, with a few very good works," dealer Emmanuel Di Donna said. "I'm amazed by the quality of material on offer," noted dealer Daniella Luxembourg.

The estimates are ambitious compared with the results of the same sales a year ago, which tallied $389 million.

Christie's sale includes eight works from the estate of Edgar M. Bronfman, the Seagram magnate and philanthropist who supported Jewish causes. Sotheby's offers three works, two by Giacometti and one by Miró, from the New York-based foundation created by art dealer Pierre Matisse and his wife Tana, all purchased directly from the artists. Sotheby's also has works from the estate of Swiss dealer Jan Krugier, including Picasso, Giacometti, Léger and Braque.

Claude Monet's oil painting Nymphéas (1907), is the top-priced lot at Christie's and appears on the catalogue's cover. Measuring just short of 40 inches high, the work is estimated to sell for up to $35 million. It shows the surface of the artist's water lily pond at Giverny.

"A fresh Monet Nymphéas represents the Holy Grail to many collectors," Andrea Crane, New York private dealer and consultant, told A.i.A. "The painting has been hidden away since 1930. There is a global market for a work like this, and collectors from all over the world could well be interested in this picture." Nymphéas comes from the holdings of Huguette Clark (1906-2011), daughter of 19th-century industrialist W.A. Clark. The art-collecting family endowed a wing at the Corcoran Gallery of Art in Washington, D.C.

"The painting hasn't been seen in public since 1926," Christie's head of department Brooke Lampley told A.i.A. in a phone interview. "It's been hanging in Huguette's apartment on Fifth Avenue ever since she bought it."

Other high-ticket items at Christie's include Wassily Kandinsky's oil-on-board Beach Scene (1909), just over 2 feet wide and estimated to bring up to $22 million. Off the market since 1975, the painting is one of nine works, by artists including Picasso, Léger, Braque and Dalí, from German collectors Viktor and Marianne Langen. Viktor Langen was the son of an industrialist family as well as an entrepreneur and inventor. The Langen works also include a pure abstraction by Kandinsky, Black Points (1937), estimated at up to $6 million.

Also from the Langens and tied with Monet for the evening's priciest lot is Picasso's Portrait of a Woman (Dora Maar), 1942, estimated to fetch up to $35 million. The oil on panel shows the artist's mistress at half-length, in a purple dress against a gray background. It's one of 13 works by the Spaniard on offer May 6.

Alberto Giacometti's figural sculpture Woman of Venice IV (1956-57) is estimated at $10 million to $18 million. The estimate for the bronze testifies to the house's confidence in the market for modernist sculpture: the same piece brought just $2.8 million at Sotheby's London in June 2000. "It's a very crisp cast, and sometimes, as here, he highlighted the sculptures with paint, which makes them even more special," Di Donna told A.i.A. The seller is not identified.

The following night, Sotheby's sale, like Christie's, includes 13 works by Picasso, along with five each by Bonnard, Degas, Giacometti and Miró.

On the cover of the sale catalogue is Giacometti's bronze sculpture La Place (1948), showing five of his trademark attenuated human figures. Measuring 24½ inches long, the work is estimated at $12 million to $18 million. The same work sold for $4.5 million at Sotheby's New York in 2000.

Henri Matisse's 1924 oil The Morning Sitting is estimated to bring up to $30 million. The 30-inch-high canvas depicts dancer and musician Henriette Darricarrère, the artist's studio assistant, at work on her own canvas. Matisse offered her free lessons, and her work would eventually be accepted into Paris's Salon des Indépendants. Sotheby's has guaranteed the unnamed American seller an undisclosed amount for the painting.

A second Matisse canvas, The Woman in Yellow (1923), also shows Darricarrère, this time with a guitar at her side; she would give up her musical pursuits the following year, owing to a bad case of stage fright, according to Sotheby's. The 2-foot-high painting is estimated at $9 million to $15 million, and comes from an unnamed Japanese collector.

"You don't have very often major works from the Nice period, in the 1920s, coming to auction," Simon Shaw, co-head of the department worldwide, told A.i.A. in a phone interview. The Matisse works come to market during the exhibition "Henri Matisse: The Cut-Outs," at London's Tate Modern (through Sept. 7), which will later come to New York's Museum of Modern Art (Oct. 25, 2014-Feb. 8, 2015).

One of the baker's dozen of Picassos is The Rescue (1932), estimated at upwards of $14 million, the same price it brought at Sotheby's New York in 2004. The oil on canvas, just over 4 feet wide, shows a bather being rescued from drowning while others play ball on the beach; all the figures have the distinctive profile of Picasso's young lover Marie-Thérèse Walter. The seller is not named.

To beef up its acquisitions fund, New York's Metropolitan Museum of Art is offering Claude Monet's landscape On the Cliffs at Pourville (1882), estimated to bring $5 million to $7 million. The 32-inch-wide canvas has been in the museum's collection since 1956.

Sotheby's also has a Giacometti Woman of Venice, this one cast in 1958 and estimated at $6 million to $8 million. The bronze figure brought $2.9 million in 2001 at Sotheby's New York. It comes from the estate of Swiss art dealer Jan Krugier, who died in 2008. Select examples from his collection came on the block in 2013 at Christie's New York with disappointing results: of the 46 works, 11 failed to sell, and the sale totaled $144.2 million, falling short of its $188 million low estimate.

Another Picasso canvas, Head of Marie-Thérèse (1932-34), was given in 1984 by the artist's widow Jacqueline Picasso to William Rubin, then director of the department of painting and sculpture at New York's Museum of Modern Art. It has never come to auction before, and is tagged at $15 million to $20 million. The seller is not identified.

"We'll see how the market will swallow so much property," Luxembourg told A.i.A. "Some of the prices are high, she said, but added, "The quest is for quality. The art market is not about buying the cheapest piece. It's about buying the best one."

The spring sales continue with auctions of postwar and contemporary art at Christie's May 13, Sotheby's May 14 and Phillips May 15.