iShares Cohen & Steers Realty Majors ( ICF) -6.8% REITs were down across the board. A list of the worst performers this past week is dominated by REITs at the bottom. Retail shares had the worst showing. Even without their internal problems, REITs were leaders in the late-summer rally, and that's reason enough for them to lead the sell-off. iPath Crude Oil Total Return ( OIL) -8.8% PowerShares DB Oil ( DBO) -7.6% United States Oil ( USO) -8.4% Oil tanked this week on higher inventory. The gap between crude oil inventory expectations and reality was about 5 million barrels, as inventories climbed more than 2 million barrels. Gasoline inventories rose by more than 5 million barrels, to a level well above the start of driving season this year. iShares Mexico ( EWW) -5.3% American Movil ( AMX) and Cemex ( CX) both fell about 5% last week, and they combine for 30% of EWW's assets (25% for AMX and 5% for CX). Cemex sold $1.8 billion worth of shares this week. The stock fell ahead of the news and then recovered.