In this writer's opinion, Calder is one of the three greatest sculptors of the 20th century (Brancusi and Henry Moore are the other two). Some might argue that this exclusive club should include Matisse, Giacometti and Picasso. Others might wonder how I could overlook David Smith.

But if you base greatness on innovation and the ways that the work affected the historical development of sculpture, you would have to go with Calder. After all, how many artists created a brand new art form -- the mobile? Thanks to Calder's genius, the concept of kinetic art (art that moves) was born.

However, enough about esthetics. What about Calder's market? During the 1980s art market boom, Calder experienced unprecedented popularity. In a way, he had the perfect market -- overwhelming demand and not quite enough supply. Though the collector could always count on seeing a few Calders at every auction, he knew that there were more than an equal number of applicants.

Calder at auction was a lot like applying to an Ivy League school. You knew there were openings each year, but you also knew that you'd have to fight like hell to get in.

When the early 1990s saw the art market crash, Calder's prices stopped going up. But unlike virtually every other artist (including Warhol), his prices never went down. In fact, you might say that Calder was the only recession-proof artist. Collectors learned that in tough times the only sure bet was Calder.

You can imagine, then, what happened when things turned around in the late 1990s -- Calder's market resumed climbing and quickly surpassed its 1980s peak.

Currently, whenever a new auction catalogue comes out, the house typically underestimates Calder's work. Normally, I would say this is par for the course -- estimates usually appear as teasers in order to stimulate bidding. When prices exceed their pre-sale estimate, it creates a feeling of euphoria. An illusion is created that the auction did well. However, over the last two sales, prices have climbed so high that consignors are now demanding estimates equal to previously realized prices. As a result, works have begun to increasingly sell within estimate.

Not so for Calder. His prices, despite their optimistic estimates, continue to exceed expectations. The days of buying even a miniature (under 12 inches in all dimensions) standing mobile for less than $150,0000 are just about at an end. These small Calder masterpieces have greatly increased in value, notably due to the fact that there are many more collectors with $150,000 to spend than $500,000 (the cost of a high-quality mobile). Besides, the miniature standing mobiles take up so little space. Even when Calder worked small the work retained its power.

During the last auction season, several Calder records were set, including one for an outdoor stabile. The giant work, Stegosaurus, appeared sporting a pre-sale estimate of $2.5 million-$3.5 million (Sotheby's, Nov. 2000). The winning bid tallied $4.1 million, shattering the old record of $640,500 (Christie's, May '95).

A new record was also achieved for a mobile. In this case, a large example brought $1 million (Christie's, Nov. 2000), breaking the old record of $682,000, set back in 1989 (Sotheby's, May). Finally, if even more evidence was needed to prove the validity of the Calder market, a small standing mobile (19 x 13 x 18 in.), painted in primary colors, brought a numbing $423,750 (Sotheby's, Nov. 2000). The estimate had been $100,000-$150,000.

What's the future of the Calder market? It's obviously a safe call to say it will continue to flourish. The large-scale standing mobiles and stabiles that were created to go outside will probably have a ceiling of $5 million. The mobiles, which are really the middle ground in the Calder market, will continue to fetch $500,000-$1 million. But the better small standing mobiles and the best small stabiles are likely to keep climbing, perhaps all the way to $500,000.