Recently Mr. Teetor, a subscriber of mine, has posted an enthusiastic comment on trading the XLE-USO spread that I suggested. While Mr. Teetor has a lot of success trading this spread, I must say that I have lost faith in the cointegrating characteristic of this spread because of two reasons:
1) The spread appeared to have experienced a regime-shift since the historic backtest period before August 2006: the out-of-sample performance of the spread since then did not support cointegration; and
2) The fundamental argument in support of cointegration between XLE and USO fell apart upon closer investigation.
The two reasons are, I believe, intertwined. Unlike GLD (part of a much more cointegrating spread that I discussed and tracked in my premium content area), USO does not actually hold commodity assets in its portfolio. It holds nearby futures contracts in oil. When the USO fund started trading in April 2006, its price per share was very close to the spot oil price. Now, however, USO is trading at about $53, while spot oil price is at about $70.6. How can a fund that is supposed to reflect oil price diverge so much from it after a year and 5 months? The reason is that the oil futures market has been in contango since 2005 or so, i.e. far month futures costs more than the nearby contracts, which results in negative roll-yield for long position in oil futures. In the historic period from which the XLE-USO cointegration relation was established, oil futures market exhibited backwardation: far month futures cost less than nearby futures. This regime shift partially explains the breakdown of the cointegration relation in the present out-of-sample period.
The lesson I have learned from all these is to avoid analyzing cointegration relation when either side of a spread involves futures contracts at different points of the forward curve, at least on a time-scale when the shape of that curve might change. (I argued before that XLE, the other side of the spread, can be modeled as an average over the entire forward curve.) Meanwhile, the fund manager of USO would really have done investors a much better favor by getting their hands dirty, leasing some oil storage tanks and buying some real oil assets rather than keeping their hands clean and dealing in futures contracts alone. After all, retail investors like myself can just as easily buy oil futures ourselves, but we can't very well go out and rent an oil tank.