shrewd, u said "All the oil majors have failed", just to clarify with some historical info:
ENI completed drilling/geological work in the Darin Basin & flowed hydrocarbons there, but the completed data from them has not been released to Range.
Conoco's data pre 1991 from the Nogal Valley stated "abundant oil shows, thick porous reservoirs, large structures and an excellent regional seal” http://www.africaoilandgas.com/download/aog.pdf