eia.gov: Crude oils have different quality characteristics
Notes: Points on the graph are labeled by country and benchmark name and are color coded to correspond with regions in the map below. The graph does not indicate price or volume output values. United States-Mars is an offshore drilling site in the Gulf of Mexico. WTI = West Texas Intermediate; LLS = Louisiana Light Sweet; FSU = Former Soviet Union; UAE = United Arab Emirates.
http://www.eia.gov/todayinenergy/detail.cfm?id=7110
API gravity