Just for fun, here is a 5 year chart of KOL over UNG. Keep in mind that a big part of this move was the contango cost in UNG which as you can see over time, is a real killer. Keep in mind, natty had a historic drop during this period as well. Use to trade in the mid teens.
As you can see when we take KOL over UNL, we get the same shape of the curve but much less pronounced. UNL really improves on the contango issue.