As of Nov. 27, DUG had lost more than $6 million in assets this month while ERY had seen only modest inflows. Again, there are parallels between equity-based oil ETFs and their futures-based counterparts.

Money has been pouring into the United States Oil Fund (NYSEArca: USO), but much of the cash that has taken USO north of $1 billion in assets under management is believed to be from traders shorting the ETF.

Interestingly, XLE, the largest energy sector ETF, has added $1.1 billion in new assets this month, which could be a sign that some traders are shorting that fund rather than establishing long positions in inverse equivalents. XOP, often one of the most heavily shorted ETFs of any type, has added $41 million in new assets this month.

UltraShort Oil & Gas ProShares