Recent U.S. imports of oil tend to be heavier than domestic production
http://www.eia.gov/todayinenergy/detail.cfm?id=26132
MAY 6, 2016

Links to supporting info at the source.
I recall Texaco, my former employer in the 80s reconfigured its refineries to run heavy crude. Idea was that, in the USA, the lighter crudes like WTI were gradually getting scarcer as these premium crudes were getting harder and harder to find and produce, and heavier, less attractive crudes were increasing.
Surprise, surprise, this trend got its legs cut out from under it when the unconventionals began producing several years ago.
Our refineries now simply cannot handle the lighter crudes unless some massive reconfiguration is undertaken.
Oh, and BTW, Texaco, which led the pack back then in doing this as a major refiner, went south and is no longer around 'cause it couldn't make up the downstream losses with its upstream business.
So much for guessing wrong.