Just wondering..

I noticed it happened today and last Friday: the price of oil was up for both days, yet USO is up more than the double long oil ETF DXO. Why is this so? For example, as of now USO is up 6.47% while DXO is up just 4.21%. USO: http://finance.yahoo.com/q?s=USO DXO: http://finance.yahoo.com/q?s=DXO