Norman Rockwell's Saying Grace became the most expensive American painting ever sold at auction last week, fetching US$46 million ($55.5 million) at Sotheby's in New York.

The next day at Christies, an anonymous buyer set a record for a painting by Rockwell's contemporary, Edward Hopper, whose Depression-era work, East Wind Over Weehawken, sold for US$40.5 million.

And yet, as recent sales go, both seem like small fry. In the space of 48 hours in November, Manhattan's two leading auction houses saw more than US$1.1 billion spent on 20th-century art, setting new records for the most expensive work sold at auction, the most expensive work by a living artist sold at auction and - with US$691 million splurged in a single evening at Christie's - the highest ever total for a single auction.

All three records had previously been broken within the past 18 months. The most expensive auctioned artwork of all, Francis Bacon's 1969 triptych, Three Studies of Lucian Freud, were sold to an anonymous buyer for US$142.4 million.

That was about US$20 million more than the last record-holder, the Norwegian painter Edvard Munch's The Scream, which was sold last year.

At the same sale, Jeff Koons' sculpture, Balloon Dog, fetched US$58.4 million, also about US$20 million more than the previous record for a living artist's work - the US$37 million paid for a painting by Gerhard Richter at Sotheby's in May.

Georgina Adam, editor-at-large for the Art Newspaper, called the sums "demented", adding: "If you're a multi-billionaire, you want trophies, but US$58 million for a Koons is bananas."

While most people are still reeling from the financial crisis, the world's wealth has risen to those at the top. A report found 2170 billionaires globally, three times as many as five years ago.

- Independent