By Mike Boehm March 18, 2014, 7:34 a.m.

Culture Monster has seen a picture of the global art market, and it looks very much like a portobello mushroom.

The glimpse came not in a photograph, painting or drawing, but from the 83-page annual “TEFAF Art Market Report” issued recently by the European Fine Art Foundation.

It found that the art business rests on a very slender stem of prized artists whose work has sprouted a vast canopy of cash, paid overwhelmingly by a coterie of 600,000 or so global millionaires who qualify as “mid- to high-level art collectors.”

The report found that 8% of the art auctioned worldwide in 2013 accounted for 82% of the money spent. In the United States, the ratio was even more skewed: 7.5% of the works auctioned raked in 91.2% of the bucks.

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While auction sales accounted for only 47% of the $63 billion or so spent on art worldwide, the report’s author, arts economist Clare McAndrew, wrote that the same phenomenon applies across the board: “a small number of [artists] accounting for an increasingly large share of total sales….is also true of the dealer market, with high-end dealers commenting that their top collectors appeared to be interested in the work of only about 50 to 100 artists.”

McAndrew ‘s report states most aggregate art sales in euros; applying average exchange rates for each year to convert them to dollars, the $63-billion sales estimate for 2013 fell a bit short of the global art market’s pre-recession peak of $65.8 billion in 2007.

The report by the Netherlands-based European Fine Art Foundation derived its estimates by crunching numbers from two major clearinghouses for art auction information (one for China, one for the rest of the world), and weaving in responses from a survey of about 5,500 art dealers who had annual sales exceeding 2 million euros (about $2.7 million).

When we’re talking about the people who really, really matter in the art market, the report informs us, we’re talking not about those 600,000 mere millionaires and their tastes, but about just under 200,000 “ultra-high net worth individuals”  (UHNWIs) who sit atop piles of $30 million or more.

These folks – a third of them Americans, by far the largest national share — command $28 trillion in wealth, we’re informed, and their art holdings account for about 1.7% of their net worth. That’s about $476 billion worth of art.

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We’re told that these UHNWIs devote about 10% of their money to “investments of passion” such as art, jewelry, other collectibles and sports — and that globally art accounts for 17 cents out of every dollar devoted to “investments of passion.”

North American rich folks are deemed the most passionate about art, devoting 19 cents out of every dollar in “passion” investments to it, compared to a nickel for sports and 31 cents for their favorite category, “other collectibles” — a grab-bag that includes antiques, rare coins, vintage wines and such.

The report says that Japanese uber-wealthy are the least art-inclined, with just a 12-cent allocation of their passionate investment buck. High rollers from all continents apparently share a fondness for bling, devoting 30 to 35 cents of  their passionate investment dollar to jewelry and gems.

The report’s most encouraging news for auctioneers and dealers patronized by the ultra-rich, and for the elect few living artists the top collectors focus on, is that “many HNWIs are increasingly approaching luxury goods as investments, and looking for those sectors that have the most long-term value, notably art and antiques.”

Such a mindset may have been at play in 2013 when Francis Bacon’s three-part painting, “Three Sides of Lucian Freud,” established a new auction record for a single work, $142 million.

Or maybe the anonymous buyer just loved it that much (the New York Times has reported that art world speculation pointed toward Elaine Wynn, who serves on the board of the Los Angeles County Museum of Art).

It may be worth remembering that for a billionaire, such a purchase is the proportional equivalent of a person whose net worth is $100,000 springing for a $14,200 used car — not exactly pocket change, but not something the neighbors would think incredibly extravagant (the median net worth of American families was $77,300 in 2010, according to the Federal Reserve — meaning half were at least that wealthy, while the other half made do with less).

An estimated 38% of the money spent on art in 2013 was spent in the United States, according to the report, although U.S. sales accounted for only 21% of the works sold.  China, which in 2011 had briefly edged past the U.S. in total expenditures for art, has fallen back into second place at 24% of global spending, although Chinese dealers and auctioneers handled nearly double the U.S. volume — 41% of the artworks moved worldwide. Note that national totals reflect art sold in a country, not art bought by its citizens. Some would be purchased by foreigners who were visiting, or who placed auction bids by phone.