A self-portrait of Andy Warhol in a spiky fright wig sold for 2.9 million pounds ($4.98 million) at Phillips yesterday in London, concluding the spring auction season in Europe.

This week’s evening sales of contemporary art at Phillips, Sotheby’s (BID) and Christie’s in the U.K. capital produced a total of 202.4 million pounds, a 28 percent jump from the tally at equivalent events last year. New buyers from China and other international markets are boosting prices for top postwar and contemporary artists, as the works are being increasingly seen as strong investments.