This week's downturn in crude oil prices has had a depressing effect on the entire commodity group. Chart 1 shows the CRB Index (plotted through Thursday) breaking a three-month up trendline (and its 50-day moving average). The 12-day Rate of Change (ROC) line (top of chart) has fallen to the lowest level in more than three months. And the daily MACD lines (bottom of chart) have turned negative after forming a "double top" between March and July. The minimum downside target is most likely a test of the 400 level which would test a yearlong support line and the early May low. I wouldn't, however, rule out a further drop to the March low at 380. The weekly CRB chart also suggests a very over-extended market in need of a correction.