DOY, the MacroShares $100 Oil Down ETF acts as an inverse ETF since it moves in the opposite direction of the spot price of West Texas Intermediate light, sweet crude oil (WTI).
The oil ETF consists of assets that are U.S. Government obligations, repurchase agreements and cash.
As of June 25, 2009 this ETF will be closed because assets on record fell below $50 million
If you'd like to see more related funds, here is a thorough list of oil ETFs and ETNs.
If you'd like to see more inverse ETFs, here is a thorough list of inverse ETFs and ETNs.

