The global art market contracted for the second straight year in 2016, falling to the lowest level since the financial crisis as economic and political volatility weighed on auction sales.

Sales of art and antiques dropped 11 percent to $56.6 billion, according to a report released on Wednesday by UBS Group AG and Art Basel. The decline, on top of a 7 percent slide in 2015, wipes out the gains seen in 2013 and 2014, when sales reached an all-time high of $68.2 billion.

“It was quite a challenging year for the art market,” Clare McAndrew, founder of Arts Economics that prepared the report, said in a telephone interview.

“It’s a really supply-driven marketplace and it’s vendors holding back,” McAndrew said in an interview with Bloomberg Television on Wednesday. “We saw it especially at the top end of the market. The private sector did fairly well, but the auction sector declined