Increasing Spread in Price of WTI Vs Bakken Sweet -- The Bakken, North Dakota, USA

Elsewhere they are talking about the increasing spread between WTI and Bakken sweet.

If the statement is accurate (that the spread is increasing), the first two things I would think of: a) continued over supply at Cushing; and, b) cost of transportation (rail is more expensive than pipeline, and we have all seen how well the pipeline story is going this month).