The USO isn't a good play on oil IMO. It invests in futures, not the underlying physical. With oil currently in contango, you are getting negative roll, which is eating away at returns.
Today is the key point with USO. One of my energy models has oil going to over 100 dollars per barrel in the times to come.
Im maintaining my call on USO. Its about 10% up from my first post. I know a lot of ET'ers frown upon a modest 10% one month return, but I am happy with it. I believe it will go higher with a short term target of $64. Longer term it will probably complete the huge cup and might even splash higher. I know its more profitable to trade oil futures with this thesis, but I dont play around with those. Im happy with my 1 month 10% return on this especially when the entire market is taking a big dive.