WARNING: Read me before buying OOO, page-144

They didn't mention clearly in their website. Only recently, they added some explanation in bond:

The price of oil futures contracts is not the same as the “spot price” of oil. As such, OOO does not aim to, and should not be expected to, provide the same return as the performance of this spot price. The performance of an ETF that is linked to oil futures may be materially different to the performance of the spot price of oil itself. This is because the process of “rolling” from one futures contract to the next to maintain investment exposure can result in either a cost or benefit to the Fund, affecting returns.

TBH, they should have stated it earlier. This is the biggest risk in investing in OOO and they were just made it vague....