The authors estimate the effect of ordering by value on revenues in sequential auctions using data from art auctions of Impressionist and Modern by Sotheby’s and Christies’ from 1985 to 2007. Sotheby’s and Christie’s agreed years ago to alternate between who holds their auction first during auction week in New York City. Since the same buyers attend both auctions, the authors use this pre-determined rotation as a natural experiment to identify the effect of ordering on revenues. When the house with the most expensive paintings goes first during the week, they find that the average sale premium for the week is around 25 percent higher relative to the unconditional mean sale premium and the fraction of paintings sold for the week is around 7 percent higher relative to the unconditional mean sold rate. These findings are consistent with theories, which predict that it is optimal to auction off expensive items first in sequential auctions of goods of heterogeneous value.