This weekend brings together two of the most important trends in the art market: fairs and auctions. As the Armory Show goes into full swing, the auction houses open their doors to show what’s on offer in their mid-season sales next week.

It’s rare to see the two sides in this game — dealers and auction houses — square off so neatly. London holds major sales timed to the Frieze Art Fair, but those auctions include some of the biggest-ticket items. This week, the focus is on the broader band of art collectors and lower price points at Phillips de Pury on Monday, Christie’s on Tuesday, and Sotheby’s on Wednesday. (But don’t get carried away: We’re still talking about five- and six-figure prices — which in this market are considered middle-market prices.)

Many of the artists whose work is being sold at the Armory Show will also have work in the auctions. The dealers usually aren’t pleased about that, but if collectors aren’t fast enough to get what they want at the fair — and they have to be fast at an art fair — there are a few second chances in the sale-rooms. In today’s marketplace, art is rationed in one of two ways. Dealers have time on their side and can keep collectors on waiting lists. Auction houses rely on prices: The highest bidder wins.

As long as the tide of collectors is still running in — and though we may have reached a high-water mark there is still no sign of an ebb (yet) — the auction houses will be offering their alternative access to artists. “Whether or not there is a waiting list,” Phillips de Pury’s director of contemporary art, Aileen Agopian, said, “this a democratic process and everyone has a fair opportunity. It’s not daunting. You don’t have to know the dealer. If you love the work you have the opportunity to take your best shot at it.”

“We thank the art fairs for bringing the publicity,” the creator of the Sotheby’s sale, Jennifer Roth, said. “It is beneficial for the entire market. More people get involved and see the variety of the art market.”

With many collectors from Europe, Asia, and the Middle East in town to take advantage of the panoply of art and the cheap dollar, the auction houses have plenty of bait.

Christie’s has many smaller works by big names such as Yoshitomo Nara, Richard Prince, Tom Wesselmann, and Albert Oehlen. There are good pieces by Sean Scully, Mike Kelley, and Dana Schutz along with some David Smith bronzes, Frank Stella drawings, and a cache of Robert Smithson works.

Sotheby’s has a broad-ranging sale. There are “lots of hot young artists and mid-career artists who might have been in the shadows for some time,” Ms. Roth said. The latter part of the sale is chockablock with works by Alexander Calder and Sam Francis but up front are lots of Pop painters like Keith Haring, Kenny Scharf, and George Condo.

Op art is well represented by a Bridget Riley and many works by Victor Vasarely. Italian collectors have led the way in bringing Vasarely back to the edge of prominence. They have also supported Italian artists Arnaldo Pomodoro and Luis Tomasello, who have works in the sale.

Zao Wou-Ki and David Smith lead the high-modernism faction. (There seem to be a lot of Smith’s paintings in these sales.) An early work from the mid-1930s by Mark Rothko should attract strong interest, too.

Sotheby’s has a number of works by appropriationist painters like Richard Pettibone, Mike Bidlo, and Louise Lawler. But the lot most likely to sell quickly and strongly is Anselm Reyle’s untitled stripe painting. Demand for these pictures is so high that it has become standard over the better part of the last year to begin an important auction in New York or London with a Reyle. Here the Reyle is not a teaser, but the main attraction.

Phillips de Pury has its own Reyle. However, the work is from an even earlier period — when the painter was in his early 20s. The Sotheby’s stripe painting is estimated at between $200,000 and $300,000, but this one carries an estimate at between $12,000 and $18,000. No doubt the experts at Phillips are being conservative.

The sale at Phillips presses on every hot sector of the contemporary market. Russian, Chinese, German Leipzig-school painters — they’re all here. Banksy, Cecily Brown, Marc Grotjahn — check. Terence Koh, Tara Donovan, and Steve Parrino are here. So is Piotr Uklanski.

There is a Damien Hirst spin-art painting in the sale, estimated at between $500,000 and $700,000, that seems a little out of place. But Ms. Agopian said, “It’s the absolute perfect commercial size. It’s a 5-foot painting.”

Besides, she said, Mr. Hirst is the godfather of contemporary art and the presence of his work “shows that he’s become the establishment figure of the cutting-edge masters.”