i posted about USO in the stocks section today on how cheap it looks, however a while back i brought up the same question on why it doesnt track the barrel....
here is something from April 2006:
Investors considering purchasing the oil ETF should tread lightly, warns Bianco Research in a Monday note. The research group points out that, according to the fund's prospectus, the average daily change in the ETF's net asset value for any period of 30 straight valuation days comes within 10%, plus or minus, of the average daily change in the benchmark oil futures contract over the same period. "A 10% tracking error? Try that in the equity index ETF world," writes the research group. The divergence is already in play Monday: While oil prices were up more than a buck, the USO ETF shed nearly 1% to $67.76.