I believe that the geolists break the oil down, looking at paraffin, carbon, sulphur content in the oils to determine specific origins. Kind of like soil samples used in forensics.
0.02
Best Regards,
Don
------------------
The most foolish mistake we could make would be to allow the subjected people to carry arms; history shows that all conquerers who have allowed their subjected people to carry arms have prepared their own fall.
Adolf Hitler