Note:
USO: US Oil Fund (Ticker: USO) holds long positions in West Texas Intermediate crude oil futures contracts, and rolls these contracts forward each month.

OIL: the IPath crude Oil ETN (exchange traded note),similar to USO which involves negative roll yields in a contango market,but also credit risk. With ETNs, you are an unsecured creditor of Barclays (the issuer of the note), so you have credit risk overlaid on the risk of the commodity.

DBO: Rather than select a new futures contract based on a predetermined schedule (e.g., monthly), each Index Commodity rolls to the futures contract which generates the best possible ‘implied roll yield.’ The futures contract with a delivery month within the next thirteen months which generates the best possible implied roll yield will be included in each Index. As a result, each Index Commodity is able to potentially maximize the roll benefits in backwardated markets and minimize the losses from rolling in contangoed markets.