U.S. crude oil production has grown rapidly in recent years, primarily from light, sweet crude (less dense, lower sulfur content) from tight resource formations. Roughly 90% of the nearly 3.0 million barrel per day (b/d) growth in production from 2011 to 2014 consisted of light, sweet grades, meaning they have an API gravity of 40 or above and a sulphur content of 0.3% or less.