Like I said, DTO uses the April futures contract which expires on March 20th, and DXO uses the July contract which expires on June 22nd. Link with the ev. Your link says the same thing, btw.
DBO is an option they roll differently, use contracts further away...thus less affected by contango, which is more pronounced at near months... it held up much better then USO relative to spot the market cap is just 46 M...have not checked spreads...may be good for long term