WTI is on balance higher quality (which is why it has almost always traded at a premium to Brent), but Nigerian & Libyan blends are very high quality within Brent -- with Libyan off the market and strife in Nigeria with Boku Harem, there are tighter supplies of Brent. On the flip side, refiners are closing on the East Coast because Cushing is the central distribution point for WTI -- plenty of supply in Cushing from Canada & NoDak, but no easy way to get large amounts to Houston or the East Coast or Europe, which would bring Brent & WTI back into their traditional spread.