Why is North Sea Brent oil always 10-13% cheaper than Sweet Light Crude? What is the difference between these oils?
Perhaps Anthracite might have something to contribute. 
The price of crude oil is determined mostly by what it is, and partly by where it is. The prices you see in the news are for crude delivered at specified terminals, so location is not a factor.
You most commonly hear references to the crude’s “lightness/heavyness” and “sweetness/sourness” when it is described. The API gravity scale is used express the relative density of petroleum liquids. High numbers (the scale goes from 0 to 100, with water set at 10) are lighter. Sweet crude has low sulfur (or carbon dioxide) content, while sour crude has high sulfur content. Light and sweet crude is the most expensive while heavy and sour crude fetches lower prices.
From NYMEX on Light, sweet crude:
It occurs to me that I might want to rethink what I said about location, as the NMEX light sweet and IPE Brent prices you see in the papers are reports from different exchanges with different preset points of delivery.
I just don’t have time right now (HouDope is imminent). Any thoughts are appreciated.
And a day later I don’t have an answer. Anybody have some thoughts on price v. point-of-delivery?