An unnamed collector, apparently a Russian, spent $11.3 million at the postwar and contemporary auction at Sotheby’s in London last week for Peter Doig’s “White Canoe” — a painting that, dealers say, would probably have gone for only $2 million or $3 million in New York. Although it was surprising, some in the art world say the high price was reflective of the general unpredictability of the London sales, where some of the major bidders are wealthy foreign nationals for whom a few million dollars is pocket change.

The results of last week’s auctions in London, while considerably smaller in financial terms than those of the most recent New York sales, certainly demonstrated the ongoing strength of the market. The Impressionist and modern art sale at Sotheby’s set a record for the largest sale ever in Europe, bringing in almost $187 million. Meanwhile, the postwar and contemporary sale at Christie’s set a record for the largest ever sale in that category in Europe, taking in just over $138 million. (By contrast, the records for largest sale, and for largest postwar and contemporary sale, were set last November at Christie’s in New York, with totals of $491 million and $239 million.) While it’s difficult to say just how much the buyers in New York and London differ, some people point to sales like “White Canoe” as evidence of the influence of London’s plentiful foreign residents.

“A lot of the activity in the art market is comparable to the activity in the London housing market,” the head of contemporary art at Sotheby’s in London, Oliver Barker, said. “What you’re seeing there is much, much higher prices as a whole group of foreign communities move in, like the Russians or the Middle Easterners or the Chinese.”

These people choose London as a base for a number of reasons, Mr. Barker said, including what he called the “wonderful tax situation for nondomiciles.” Foreign residents in Britain only have to pay tax on income they earn in the country, meaning that plutocrats can successfully shield their wealth from taxes by putting it offshore.

British journalists describe the country as having become a virtual tax haven for the superrich, and some in the art world think this contributes to some works, like “White Canoe,” selling for far greater than their expected value. In another instance, at Christie’s contemporary art sale in London last year, a Russian collector bought a Warhol dollar-sign painting for $5 million, or five times its estimate. (It was rumored that Christie’s was in the end unable to collect from a source of funds that they considered legitimate. A Christie’s spokeswoman, contacted for comment, did not return an e-mail or phone calls to her home.)

“If you look at the last couple of years of London, you see these ridiculous spikes in price on certain things,” a director of the Richard Gray Gallery in New York, Andrew Fabricant, said. “You have that in New York on occasion, but it’s substantiated by known people bidding on it — longstanding dealers, longstanding collectors. Everyone basically knows what’s going on. In London, there are often cases where things are sailing out of the sales room, and you don’t know who’s doing what.” Last week, Mr. Fabricant was the winning bidder on the top lot at the Christie’s postwar and contemporary sale, Francis Bacon’s “Study for Portrait II.”

What do the Russians and other foreign nationals in London want to buy? “They like trophy pictures,” the director of the Impressionist and modern art department at Sotheby’s London, Philip Hook, said. Also, he said, Marc “Chagall and [Chaïm] Soutine have benefited from Russian interest, in that they are both artists with Russian origins.” The top lot at the Sotheby’s Impressionist and modern sale last week was Soutine’s “L’Homme au Foulard Rouge,” which went for $17 million. There is no indication that the buyer was Russian — the winning bidder was reportedly an art consultant, Maria de Madariaga — but Russian interest contributed to the high price, Mr. Hook said.

In the contemporary field, these buyers’ taste “tends to run to figurative art, flashier pictures,” said a dealer who did not wish to be named. “You couldn’t sell [Donald] Judd and [Sol] Lewitt and Agnes Martin and things like that, [but] they’ll buy [Miquel] Barceló, they’ll buy [Anselm] Kiefer for a lot of money, certainly Warhol.”

The second and third highest lots in the Christie’s postwar and contemporary sale were Warhols: “Brigitte Bardot,” which sold for $10.6 million, and “Three Women,” which sold for $8.3 million.

“For certain types of Warhols, London is the best marketplace,” the director of postwar and contemporary art at Christie’s in London, Pilar Ordovas, said.

Not everyone, though, is convinced that there’s an appreciable difference between the markets in New York and London.

“It is such an international world today,” the New York dealer Robert Mnuchin, of the gallery L & M Arts, said. “There is so much information out there that people who are interested in art know [about a sale] whether it takes place in Paris or London or New York or anywhere else, so I wouldn’t see why they wouldn’t all be interchangeable.”

“Russians maybe gravitate slightly more easily to London than to New York, but there’s plenty of Russian bidding in New York, as well,” Mr. Hook said. “I don’t that is really a particularly significant issue.”

If the market has become completely global, why are the auction houses so intent on cultivating London as a location for sales and projecting the idea that it is a market of equal stature to New York? One reason, of course, is that they need to develop relationships with potential sellers in Europe. Another one is that having two major markets is a way of hedging against unpredictable world events, like terrorism or tax increases.

“Strategically you never know how the future is going to pan out, and it’s always good to have two possible venues,” Mr. Hook said. “Supposing something drastic happened in America, which for one reason or another meant that it wasn’t the right thing to hold great modern art sales there for the time being. Then you want somewhere with an established track record as an alternative. Equally, supposing taxation in Europe suddenly rose up to unsustainable levels, or the VAT [Value Added Tax] on works of art got imposed to such a level that it wasn’t worthwhile to bring works of art into Europe anymore, then it’s good to have New York as the alternative.”