Christie’s International, the world’s leading auction house by revenue, reported a 5 percent decline in annual sales following five straight years of growth, a sign that the art market may be slowing amid stock price volatility and greater selectivity by wealthy buyers.

Sales of art and collectibles fell to 4.8 billion pounds in 2015, or $7.4 billion using a sales weighted currency exchange rate, Christie’s said in a statement, from about 5.1 billion pounds in 2014. Sales of postwar and contemporary art, Old Masters, 19th century and Russian art declined.

Roiling equity and bond markets, plummeting oil prices and economic weakness in China are crimping billionaires’ appetite for buying art. Despite records for individual masterpieces in 2015, sales in three key categories have contracted at the major auction houses and the outlook for 2016 is less optimistic, according to a survey by researcher ArtTactic published Monday.

“The froth is starting to come off,” Anders Petterson, founder and managing director of ArtTactic, said in a telephone interview. “Looking back, in terms of auction sales, 2014 was the peak of the market.”

Christie’s, which is privately owned by French billionaire Francois Pinault, doesn’t report profit or loss.

‘Exponential Growth’

Sales at Sotheby’s totaled $6.7 billion in 2015, unchanged from 2014, spokesman Dan Abernethy said in an e-mail.

Christie’s saw declines in several categories. Its postwar and contemporary auctions fell 14 percent to 1.5 billion pounds. Auctions of Old Masters, 19th century and Russian art declined 37 percent to 154.9 million. Private sales were down 39 percent to 554.9 million pounds.

Postwar and contemporary art “has seen an exponential growth in the past 10 years,” Stephen Brooks, Christie’s deputy chief executive officer, said in a telephone interview. “It won’t come as a surprise to me if we see some moderation in that arena.”

Impressionist and modern art countered the decline in contemporary art, rising 57 percent to 1.3 billion pounds. Christie’s boosted the segment by organizing additional themed, cross-category auctions, led by 20th century masterpieces. The industry’s top three results of 2015 were achieved during these auctions in May and November in New York.