Oh, the oddity of trading/owning commodity based ETFs. The May Crude Oil contract which expires on Tuesday just traded below $3/barrel The June price is $22/barrel. That ETF owns about 1/4 of all the May contracts so if does not want to have to deliver or take delivery of a barrel of oil it has to sell those contracts. It will then roll that money into the June and July and out contracts, and the number of shares of the USO that people own will probably go down. And this could happen again next month.
I can't think of a single reason to buy into the USO ETF anytime soon. Since the objective of USO is to track with the daily percentage changes the spot price of WTI, they are usually buying contracts that are 2-4 months out, and in the current environment, selling them close to expiration.
At this moment:
May contracts $3.94 (settles today)
Jun contracts $14.95 (settles 19 May)
July contracts $23.08 (settles 22 Jun)
Aug contracts $25.70 (settles 21 Jul)
Sep contracts: $27.22 (settles 20 Aug)
USO is having to buy contracts in the out months (Aug/Sep) for 70-80% over the price of the upcoming front month (Jun), the month that it will be mostly selling. And the likelihood is that the front month price deteriorates faster than the out months, making the buy-sell difference even greater. Even when demand picks up significantly, the oversupply in storage is worked down, and IF oil producing countries remain steady in cutting back on production, it will be months before USO isn't buying high and selling low.