The market for fine and decorative arts roared through the start of 2011 at the world's two biggest auction houses. Christie’s reported worldwide sales for the first half of 2011 of $3.2 billion, up 15% over last year's figures. Sotheby's just breezed through a summer of blockbuster sales in London totaling in excess of £365 million ($589 million), including 49 artist record prices.

Among the 95 works sold for over $1 million during Sotheby's four-week series, a Venetian scene by Francesco Guardi fetched a record $42.86 million while an Egon Schiele painting brought an astonishing record price of $40 million, adding to the $2.9 billion in sales that Sotheby's is expected to announce for the first half of the year.

Christie's biggest sales so far this year include Andy Warhol's $38.4 million "Self-Portrait" and Mark Rothko's $33.6 million "Untitled No. 17," part of $702.6 million in post-war and contemporary art sales, up 52% from a year ago. Sales for American paintings dropped by 31%, to $26.5 million, while Asian art went up by 58%, to $581.4 million.

Strong prices for top lots reflect buyers' quest for the "best of the best' as they build collections in the Medici-style across disciplines, say some experts.

Buyers were selective. Sotheby's Old Master & British Drawings sale sold just 50% by lot even while the strength of certain star lots boosted the season's Old Masters category to a hefty total of £133.8 million ($214 million).

New bidders increased by 14% at Christie's this year. A growing client base is coming from mainland China, the largest market for wine and Asian art, however, Continental Europe, the US and the UK continue to account for the firm's highest proportion of new clients (78%).

Private sales made through Christie's jumped by 57% this year to $467.3 million. The exploding private sales sector can also be seen with the oil-rich nation of Qatar, named by The Art Newspaper as the world's biggest buyer of contemporary art, and rumored to have been behind major private sales such as the $310 million Merkin Rothkos. Qatar, in fact, tapped Christie's chairman Edward Dolman to build a state collection and oversee the Qatar Museums Authority (QMA).

The middle range of the market, works at about £500,000-1 million, has also been solid, according to Christie's. The average sell-through rate is in excess of 90% for this price level.

This bullish buying trend might soon be dampened, warns a market report from ArtTactic. A survey showed that economic uncertainty and fear about the European debt crisis are seen as mounting risks to the global economy that will trickle down to the art market.

The art market has slowly recovered since the 2008 banking crisis. Yet, ArtTactic's "Risk Barometer" now reads at 12.6%, the same level as right before the Lehman collapse.

Still, ArtTactic reports that its so-called Contemporary Art Market Confidence Indicator was up by 8.3% in the first half of 2011.

Some experts believe that buyers will continue to put their cash into art as an investment, as long as sellers offer top-quality lots. The year's early sales results, too, are "a clear indication of the enduring vigour and passion for great works of art throughout the world,” says Christie's CEO, Steven P. Murphy.